Merge remote-tracking branch 'origin/main' into net7.0

Make.config

@@ -213,6 +213,10 @@ XCODE_URL=https://dl.internalx.com/internal-files/xcodes/Xcode_13.3.xip
 XCODE_DEVELOPER_ROOT=/Applications/Xcode_13.3.0.app/Contents/Developer
 XCODE_PRODUCT_BUILD_VERSION:=$(shell /usr/libexec/PlistBuddy -c 'Print :ProductBuildVersion' $(XCODE_DEVELOPER_ROOT)/../version.plist 2>/dev/null || echo "    $(shell tput setaf 1 2>/dev/null)The required Xcode ($(XCODE_VERSION)) is not installed in $(basename $(basename $(XCODE_DEVELOPER_ROOT)))$(shell tput sgr0 2>/dev/null)" >&2)
 
+# Tell both Xcode and our build logic which Xcode we're using.
+export DEVELOPER_DIR=$(XCODE_DEVELOPER_ROOT)
+export MD_APPLE_SDK_ROOT=$(abspath $(XCODE_DEVELOPER_ROOT)/../..)
+
 # Mono version embedded in XI/XM (NEEDED_MONO_VERSION/BRANCH) are specified in mk/mono.mk
 include $(TOP)/mk/mono.mk
 MONO_HASH := $(NEEDED_MONO_VERSION)

msbuild/Xamarin.Mac.Tasks.Core/Tasks/DetectSdkLocationsTaskBase.cs

@@ -1,19 +0,0 @@
-using Xamarin.MacDev.Tasks;
-using Xamarin.MacDev;
-
-namespace Xamarin.Mac.Tasks
-{
-	public abstract class DetectSdkLocationsTaskBase : DetectSdkLocationsCoreTaskBase
-	{
-		protected override IAppleSdkVersion GetDefaultSdkVersion ()
-		{
-			var v = CurrentSdk.GetInstalledSdkVersions (false);
-			return v.Count > 0 ? v [v.Count - 1] : AppleSdkVersion.UseDefault;
-		}
-
-		protected override string GetDefaultXamarinSdkRoot ()
-		{
-			return Sdks.XamMac.FrameworkDirectory;
-		}
-	}
-}

msbuild/Xamarin.Mac.Tasks/Tasks/DetectSdkLocations.cs

@@ -1,7 +0,0 @@
-namespace Xamarin.Mac.Tasks
-{
-	public class DetectSdkLocations : DetectSdkLocationsTaskBase
-	{
-
-	}
-}

msbuild/Xamarin.MacDev.Tasks.Core/Tasks/DSymUtilTaskBase.cs

@@ -55,7 +55,13 @@ namespace Xamarin.MacDev.Tasks
 			args.Add ("dsymutil");
 			args.Add ("-num-threads");
 			args.Add ("4");
-			args.Add ("-z");
+			if (AppleSdkSettings.XcodeVersion < new Version (13, 3)) {
+				// Apple removed the -z / --minimize option in Xocde 13.3, so now if you use it you get a warning: "ignoring unknown option: -z"
+				// So just don't pass -z when Xcode >= 13.3
+				// Ref: https://github.com/llvm/llvm-project/commit/5d07dc897707f877c45cab6c7e4b65dad7d3ff6d
+				// Ref: https://github.com/dotnet/runtime/issues/66770
+				args.Add ("-z");
+			}
 			args.Add ("-o");
 			args.Add (dSymDir);
 

msbuild/Xamarin.MacDev.Tasks.Core/Tasks/DetectSdkLocationCoreTaskBase.cs

@@ -73,8 +73,36 @@ namespace Xamarin.MacDev.Tasks {
 			}
 		}
 
-		protected abstract string GetDefaultXamarinSdkRoot ();
-		protected abstract IAppleSdkVersion GetDefaultSdkVersion ();
+		string GetDefaultXamarinSdkRoot ()
+		{
+			switch (Platform) {
+			case ApplePlatform.iOS:
+			case ApplePlatform.TVOS:
+			case ApplePlatform.WatchOS:
+			case ApplePlatform.MacCatalyst:
+				return Sdks.XamIOS.SdkDir;
+			case ApplePlatform.MacOSX:
+				return Sdks.XamMac.FrameworkDirectory;
+			default:
+				throw new InvalidOperationException (string.Format (MSBStrings.InvalidPlatform, Platform));
+			}
+		}
+
+		IAppleSdkVersion GetDefaultSdkVersion ()
+		{
+			switch (Platform) {
+			case ApplePlatform.iOS:
+			case ApplePlatform.TVOS:
+			case ApplePlatform.WatchOS:
+			case ApplePlatform.MacCatalyst:
+				return AppleSdkVersion.UseDefault;
+			case ApplePlatform.MacOSX:
+				var v = CurrentSdk.GetInstalledSdkVersions (false);
+				return v.Count > 0 ? v [v.Count - 1] : AppleSdkVersion.UseDefault;
+			default:
+				throw new InvalidOperationException (string.Format (MSBStrings.InvalidPlatform, Platform));
+			}
+		}
 
 		protected string GetEnvironmentVariableOverride ()
 		{
@@ -147,6 +175,10 @@ namespace Xamarin.MacDev.Tasks {
 
 		public override bool Execute ()
 		{
+			AppleSdkSettings.Init ();
+
+			SetIsSimulator ();
+
 			// If XamarinSdkRoot is set, then make that override any other value, and in order to do so,
 			// set the corresponding environment variable accordingly.
 			if (!string.IsNullOrEmpty (XamarinSdkRoot))
@@ -159,6 +191,25 @@ namespace Xamarin.MacDev.Tasks {
 			return !Log.HasLoggedErrors;
 		}
 
+		void SetIsSimulator ()
+		{
+			switch (Platform) {
+			case ApplePlatform.MacCatalyst:
+			case ApplePlatform.MacOSX:
+				return;
+			}
+
+			TargetArchitecture architectures;
+			if (string.IsNullOrEmpty (TargetArchitectures) || !Enum.TryParse (TargetArchitectures, out architectures))
+				architectures = TargetArchitecture.Default;
+
+			if (!string.IsNullOrEmpty (IsDotNetSimulatorBuild)) {
+				SdkIsSimulator = string.Equals (IsDotNetSimulatorBuild, "true", StringComparison.OrdinalIgnoreCase);
+			} else {
+				SdkIsSimulator = (architectures & (TargetArchitecture.i386 | TargetArchitecture.x86_64)) != 0;
+			}
+		}
+
 		protected bool EnsureAppleSdkRoot ()
 		{
 			var currentSdk = CurrentSdk;

msbuild/Xamarin.MacDev.Tasks/Tasks/DetectSdkLocations.cs

@@ -1,16 +1,16 @@
 using System;
+
 using Microsoft.Build.Framework;
+
 using Xamarin.Messaging.Build.Client;
 
-namespace Xamarin.iOS.Tasks
-{
-	public class DetectSdkLocations : DetectSdkLocationsTaskBase, ICancelableTask
-	{
+namespace Xamarin.MacDev.Tasks {
+	public class DetectSdkLocations : DetectSdkLocationsCoreTaskBase, ICancelableTask {
 		const string SdkVersionDefaultValue = "default";
 
 		public override bool Execute ()
 		{
-			if (!ShouldExecuteRemotely())
+			if (!ShouldExecuteRemotely ())
 				return base.Execute ();
 
 			// The new targets do not support the "default" value for the MtouchSdkVersion

msbuild/Xamarin.Shared/Xamarin.Shared.targets

@@ -41,7 +41,6 @@ Copyright (C) 2018 Microsoft. All rights reserved.
 	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.CompileITunesMetadata" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.CreateAssetPack" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.CreateEmbeddedResources" AssemblyFile="$(_TaskAssemblyName)" />
-	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.DetectSdkLocations" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.DetectSigningIdentity" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.FindWatchOS2AppBundle" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' != 'macOS'" TaskName="Xamarin.iOS.Tasks.GetMlaunchArguments" AssemblyFile="$(_TaskAssemblyName)" />
@@ -57,7 +56,6 @@ Copyright (C) 2018 Microsoft. All rights reserved.
 	<!-- Xamarin.Mac-specific tasks. Some of these are duplicated with the Xamarin.iOS ones above, and should eventually be re-namespaced to be in Xamarin.MacDev -->
 	<UsingTask Condition="'$(_PlatformName)' == 'macOS'" TaskName="Xamarin.Mac.Tasks.CompileAppManifest" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' == 'macOS'" TaskName="Xamarin.Mac.Tasks.CreateEmbeddedResources" AssemblyFile="$(_TaskAssemblyName)" />
-	<UsingTask Condition="'$(_PlatformName)' == 'macOS'" TaskName="Xamarin.Mac.Tasks.DetectSdkLocations" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' == 'macOS'" TaskName="Xamarin.Mac.Tasks.DetectSigningIdentity" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' == 'macOS'" TaskName="Xamarin.Mac.Tasks.Mmp" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask Condition="'$(_PlatformName)' == 'macOS'" TaskName="Xamarin.Mac.Tasks.PrepareNativeReferences" AssemblyFile="$(_TaskAssemblyName)" />
@@ -88,6 +86,7 @@ Copyright (C) 2018 Microsoft. All rights reserved.
 	<UsingTask TaskName="Xamarin.MacDev.Tasks.CompileProductDefinition" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask TaskName="Xamarin.MacDev.Tasks.ComputeCodesignItems" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask TaskName="Xamarin.MacDev.Tasks.DetectDebugNetworkConfiguration" AssemblyFile="$(_TaskAssemblyName)" />
+	<UsingTask TaskName="Xamarin.MacDev.Tasks.DetectSdkLocations" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask TaskName="Xamarin.MacDev.Tasks.Ditto" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask TaskName="Xamarin.MacDev.Tasks.DSymUtil" AssemblyFile="$(_TaskAssemblyName)" />
 	<UsingTask TaskName="Xamarin.MacDev.Tasks.EmbedProvisionProfile" AssemblyFile="$(_TaskAssemblyName)" />

msbuild/Xamarin.iOS.Tasks.Core/Tasks/DetectSdkLocationsTaskBase.cs

@@ -1,37 +0,0 @@
-using System;
-
-using Xamarin.MacDev.Tasks;
-using Xamarin.MacDev;
-
-namespace Xamarin.iOS.Tasks
-{
-	public abstract class DetectSdkLocationsTaskBase : DetectSdkLocationsCoreTaskBase
-	{
-		protected override IAppleSdkVersion GetDefaultSdkVersion ()
-		{
-			return AppleSdkVersion.UseDefault;
-		}
-
-		public override bool Execute ()
-		{
-			AppleSdkSettings.Init ();
-
-			TargetArchitecture architectures;
-			if (string.IsNullOrEmpty (TargetArchitectures) || !Enum.TryParse (TargetArchitectures, out architectures))
-				architectures = TargetArchitecture.Default;
-
-			if (!string.IsNullOrEmpty (IsDotNetSimulatorBuild)) {
-				SdkIsSimulator = string.Equals (IsDotNetSimulatorBuild, "true", StringComparison.OrdinalIgnoreCase);
-			} else {
-				SdkIsSimulator = (architectures & (TargetArchitecture.i386 | TargetArchitecture.x86_64)) != 0;
-			}
-
-			return base.Execute ();
-		}
-
-		protected override string GetDefaultXamarinSdkRoot ()
-		{
-			return Sdks.XamIOS.SdkDir;
-		}
-	}
-}

src/CoreText/Adapter.cs

@@ -27,6 +27,8 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 
@@ -62,58 +64,72 @@ namespace CoreText {
 				: b;
 		}
 
-		public static int? GetInt32Value (IDictionary<NSObject, NSObject> dictionary, NSObject key)
+		public static int? GetInt32Value (IDictionary<NSObject, NSObject> dictionary, NSObject? key)
 		{
+			if (key is null)
+				return null;
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return null;
 			return ((NSNumber) value).Int32Value;
 		}
 
-		public static nuint? GetUnsignedIntegerValue (IDictionary<NSObject, NSObject> dictionary, NSObject key)
+		public static nuint? GetUnsignedIntegerValue (IDictionary<NSObject, NSObject> dictionary, NSObject? key)
 		{
+			if (key is null)
+				return null;
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return null;
 			return ((NSNumber) value).NUIntValue;
 		}
 
-		public static T[] GetNativeArray<T> (NSDictionary dictionary, NSObject key, Converter<NativeHandle, T> converter)
+		public static T[]? GetNativeArray<T> (NSDictionary dictionary, NSObject? key, Converter<NativeHandle, T> converter)
 		{
+			if (key is null)
+				return null;
 			var cfArrayRef = CFDictionary.GetValue (dictionary.Handle, key.Handle);
 			if (cfArrayRef == NativeHandle.Zero || CFArray.GetCount (cfArrayRef) == 0)
 				return new T [0];
 			return NSArray.ArrayFromHandle (cfArrayRef, converter);
 		}
 
-		public static float? GetSingleValue (IDictionary<NSObject, NSObject> dictionary, NSObject key)
+		public static float? GetSingleValue (IDictionary<NSObject, NSObject> dictionary, NSObject? key)
 		{
+			if (key is null)
+				return null;
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return null;
 			return ((NSNumber) value).FloatValue;
 		}
 
-		public static string[] GetStringArray (IDictionary<NSObject, NSObject> dictionary, NSObject key)
+		public static string[]? GetStringArray (IDictionary<NSObject, NSObject> dictionary, NSObject? key)
 		{
+			if (key is null)
+				return null;
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return Array.Empty<string> ();
-			return CFArray.StringArrayFromHandle (value.Handle);
+			return CFArray.StringArrayFromHandle (value.Handle)!;
 		}
 
-		public static string GetStringValue (IDictionary<NSObject, NSObject> dictionary, NSObject key)
+		public static string? GetStringValue (IDictionary<NSObject, NSObject> dictionary, NSObject? key)
 		{
+			if (key is null)
+				return null;
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return null;
 			return ((NSString) value).ToString ();
 		}
 
-		public static uint? GetUInt32Value (IDictionary<NSObject, NSObject> dictionary, NSObject key)
+		public static uint? GetUInt32Value (IDictionary<NSObject, NSObject> dictionary, NSObject? key)
 		{
+			if (key is null)
+				return null;
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return null;
 			return ((NSNumber) value).UInt32Value;
 		}
@@ -121,13 +137,15 @@ namespace CoreText {
 		public static bool? GetBoolValue (NSDictionary dictionary, NSObject key)
 		{
 			var value = dictionary [key];
-			if (value == null)
+			if (value is null)
 				return null;
 			return ((NSNumber) value).BoolValue;
 		}
 
 		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, int? value)
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			if (value.HasValue)
 				dictionary [key] = new NSNumber (value.Value);
 			else
@@ -136,6 +154,8 @@ namespace CoreText {
 
 		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, float? value)
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			if (value.HasValue)
 				dictionary [key] = new NSNumber (value.Value);
 			else
@@ -144,6 +164,8 @@ namespace CoreText {
 
 		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, uint? value)
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			if (value.HasValue)
 				dictionary [key] = new NSNumber (value.Value);
 			else
@@ -152,6 +174,8 @@ namespace CoreText {
 
 		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, bool? value)
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			if (value.HasValue)
 				dictionary [key] = new NSNumber (value.Value);
 			else
@@ -160,45 +184,55 @@ namespace CoreText {
 
 		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, nuint? value)
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			if (value.HasValue)
 				dictionary [key] = new NSNumber (value.Value);
 			else
 				dictionary.Remove (key);
 		}
 
-		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, IEnumerable<string> value)
+		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, IEnumerable<string>? value)
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			List<string> v;
-			if (value == null || (v = new List<string>(value)).Count == 0)
-				SetValue (dictionary, key, (NSObject) null);
+			if (value is null || (v = new List<string>(value)).Count == 0)
+				SetValue (dictionary, key, (NSObject?) null);
 			else
 				using (var array = NSArray.FromStrings (v.ToArray ()))
 					SetValue (dictionary, key, array);
 		}
 
-		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, NSObject value)
+		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, NSObject? value)
 		{
-			if (value != null)
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
+			if (value is not null)
 				dictionary [key] = value;
 			else
 				dictionary.Remove (key);
 		}
 
-		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, string value)
+		public static void SetValue (IDictionary<NSObject, NSObject> dictionary, NSObject key, string? value)
 		{
-			if (value == null)
-				SetValue (dictionary, key, (NSObject) null);
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
+			if (value is null)
+				SetValue (dictionary, key, (NSObject?) null);
 			else
 				using (var s = new NSString (value))
 					SetValue (dictionary, key, (NSObject) s);
 		}
 
-		public static void SetNativeValue<T> (NSDictionary dictionary, NSObject key, IEnumerable<T> value)
+		public static void SetNativeValue<T> (NSDictionary dictionary, NSObject key, IEnumerable<T>? value)
 			where T : INativeObject
 		{
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
 			List<NativeHandle> v;
-			if (value == null || (v = GetHandles (value)).Count == 0) 
-				SetNativeValue (dictionary, key, (INativeObject) null);
+			if (value is null || (v = GetHandles (value)).Count == 0) 
+				SetNativeValue (dictionary, key, (INativeObject?) null);
 			else 
 				using (var array = CFArray.FromIntPtrs (v.ToArray ()))
 					SetNativeValue (dictionary, key, array);
@@ -213,9 +247,11 @@ namespace CoreText {
 			return v;
 		}
 
-		public static void SetNativeValue (NSDictionary dictionary, NSObject key, INativeObject value)
+		public static void SetNativeValue (NSDictionary dictionary, NSObject key, INativeObject? value)
 		{
-			if (value != null) {
+			if (key is null)
+				throw new ArgumentOutOfRangeException (nameof (key));
+			if (value is not null) {
 				AssertWritable (dictionary);
 				CFMutableDictionary.SetValue (dictionary.Handle, key.Handle, value.Handle);
 			}

src/CoreText/CTBaselineClass.cs

@@ -25,6 +25,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 
 using ObjCRuntime;
@@ -44,12 +47,12 @@ namespace CoreText {
 
 	static partial class CTBaselineClassID {
 #if !NET
-		public static readonly NSString Roman;
-		public static readonly NSString IdeographicCentered;
-		public static readonly NSString IdeographicLow;
-		public static readonly NSString IdeographicHigh;
-		public static readonly NSString Hanging;
-		public static readonly NSString Math;
+		public static readonly NSString? Roman;
+		public static readonly NSString? IdeographicCentered;
+		public static readonly NSString? IdeographicLow;
+		public static readonly NSString? IdeographicHigh;
+		public static readonly NSString? Hanging;
+		public static readonly NSString? Math;
 
 		static CTBaselineClassID ()
 		{
@@ -63,7 +66,7 @@ namespace CoreText {
 		}
 #endif
 
-		public static NSString ToNSString (CTBaselineClass key)
+		public static NSString? ToNSString (CTBaselineClass key)
 		{
 			switch (key) {
 				case CTBaselineClass.Roman:                return Roman;
@@ -79,12 +82,12 @@ namespace CoreText {
 
 		public static CTBaselineClass FromHandle (IntPtr handle)
 		{
-			if (handle == Roman.Handle)                return CTBaselineClass.Roman;
-			if (handle == IdeographicCentered.Handle)  return CTBaselineClass.IdeographicCentered;
-			if (handle == IdeographicLow.Handle)       return CTBaselineClass.IdeographicLow;
-			if (handle == IdeographicHigh.Handle)      return CTBaselineClass.IdeographicHigh;
-			if (handle == Hanging.Handle)              return CTBaselineClass.Hanging;
-			if (handle == Math.Handle)                 return CTBaselineClass.Math;
+			if (handle == Roman?.Handle)                return CTBaselineClass.Roman;
+			if (handle == IdeographicCentered?.Handle)  return CTBaselineClass.IdeographicCentered;
+			if (handle == IdeographicLow?.Handle)       return CTBaselineClass.IdeographicLow;
+			if (handle == IdeographicHigh?.Handle)      return CTBaselineClass.IdeographicHigh;
+			if (handle == Hanging?.Handle)              return CTBaselineClass.Hanging;
+			if (handle == Math?.Handle)                 return CTBaselineClass.Math;
 
 			throw new ArgumentOutOfRangeException ("handle");
 		}
@@ -98,8 +101,8 @@ namespace CoreText {
 
 	static partial class CTBaselineFontID {
 #if !NET
-		public static readonly NSString Reference;
-		public static readonly NSString Original;
+		public static readonly NSString? Reference;
+		public static readonly NSString? Original;
 
 		static CTBaselineFontID ()
 		{
@@ -109,7 +112,7 @@ namespace CoreText {
 		}
 #endif // !NET
 
-		public static NSString ToNSString (CTBaselineFont key)
+		public static NSString? ToNSString (CTBaselineFont key)
 		{
 			switch (key) {
 				case CTBaselineFont.Reference: return Reference;

src/CoreText/CTFont.Generator.cs

@@ -25,6 +25,8 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 using CoreFoundation;
 
 namespace CoreText {

src/CoreText/CTFont.cs

@@ -251,13 +251,13 @@ namespace CoreText {
 		public CTFontFeatures (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
 		public NSDictionary Dictionary {get; private set;}
 
-		public string Name {
+		public string? Name {
 			get {return Adapter.GetStringValue (Dictionary, CTFontFeatureKey.Name);}
 			set {Adapter.SetValue (Dictionary, CTFontFeatureKey.Name, value);}
 		}
@@ -280,7 +280,7 @@ namespace CoreText {
 			}
 		}
 
-		public IEnumerable<CTFontFeatureSelectors> Selectors {
+		public IEnumerable<CTFontFeatureSelectors>? Selectors {
 			get {
 				return Adapter.GetNativeArray (Dictionary, CTFontFeatureKey.Selectors,
 						d => CTFontFeatureSelectors.Create (FeatureGroup, Runtime.GetNSObject<NSDictionary> (d)!));
@@ -313,7 +313,7 @@ namespace CoreText {
 		public CTFontFeatureSelectors (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -411,7 +411,7 @@ namespace CoreText {
 			}
 		}
 
-		public string Name {
+		public string? Name {
 			get {return Adapter.GetStringValue (Dictionary, CTFontFeatureSelectorKey.Name);}
 			set {Adapter.SetValue (Dictionary, CTFontFeatureSelectorKey.Name, value);}
 		}
@@ -1680,7 +1680,7 @@ namespace CoreText {
 		internal CTFontFeatureSettings (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -1715,7 +1715,7 @@ namespace CoreText {
 		public CTFontVariationAxes (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -1741,7 +1741,7 @@ namespace CoreText {
 			set {Adapter.SetValue (Dictionary, CTFontVariationAxisKey.DefaultValue, value);}
 		}
 
-		public string Name {
+		public string? Name {
 			get {return Adapter.GetStringValue (Dictionary, CTFontVariationAxisKey.Name);}
 			set {Adapter.SetValue (Dictionary, CTFontVariationAxisKey.Name, value);}
 		}
@@ -1779,7 +1779,7 @@ namespace CoreText {
 		public CTFontVariation (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -1842,7 +1842,7 @@ namespace CoreText {
 		static IntPtr Create (CTFontDescriptor descriptor, nfloat size)
 		{
 			if (descriptor is null)
-				throw new ArgumentNullException (nameof (descriptor));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (descriptor));
 			var handle = CTFontCreateWithFontDescriptor (descriptor.Handle, size, IntPtr.Zero);
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -1860,7 +1860,7 @@ namespace CoreText {
 		static IntPtr Create (CTFontDescriptor descriptor, nfloat size, ref CGAffineTransform matrix)
 		{
 			if (descriptor is null)
-				throw new ArgumentNullException (nameof (descriptor));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (descriptor));
 			var handle = CTFontCreateWithFontDescriptor (descriptor.Handle, size, ref matrix);
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -1886,7 +1886,7 @@ namespace CoreText {
 		static IntPtr Create (string name, nfloat size, CTFontOptions options)
 		{
 			if (name is null)
-				throw new ArgumentNullException (nameof (name));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (name));
 			var n = CFString.CreateNative (name);
 			try {
 				var handle = CTFontCreateWithNameAndOptions (n, size, IntPtr.Zero, (nuint) (ulong) options);
@@ -1925,7 +1925,7 @@ namespace CoreText {
 		static IntPtr Create (string name, nfloat size, ref CGAffineTransform matrix, CTFontOptions options)
 		{
 			if (name is null)
-				throw new ArgumentNullException (nameof (name));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (name));
 			var n = CFString.CreateNative (name);
 			try {
 				var handle = CTFontCreateWithNameAndOptions (n, size, ref matrix, (nuint) (ulong) options);
@@ -1964,7 +1964,7 @@ namespace CoreText {
 		static IntPtr Create (CTFontDescriptor descriptor, nfloat size, CTFontOptions options)
 		{
 			if (descriptor is null)
-				throw new ArgumentNullException (nameof (descriptor));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (descriptor));
 			var handle = CTFontCreateWithFontDescriptorAndOptions (descriptor.Handle, size, IntPtr.Zero, (nuint) (ulong) options);
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -1998,7 +1998,7 @@ namespace CoreText {
 		static IntPtr Create (CTFontDescriptor descriptor, nfloat size, CTFontOptions options, ref CGAffineTransform matrix)
 		{
 			if (descriptor is null)
-				throw new ArgumentNullException (nameof (descriptor));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (descriptor));
 			var handle = CTFontCreateWithFontDescriptorAndOptions (descriptor.Handle, size, ref matrix, (nuint) (ulong) options);
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -2027,7 +2027,7 @@ namespace CoreText {
 		static IntPtr Create (CGFont font, nfloat size, CGAffineTransform transform, CTFontDescriptor descriptor)
 		{
 			if (font is null)
-				throw new ArgumentNullException (nameof (font));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			var handle = CTFontCreateWithGraphicsFont (font.Handle, size, ref transform, descriptor.GetHandle ());
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -2045,7 +2045,7 @@ namespace CoreText {
 		static IntPtr Create (CGFont font, nfloat size, CTFontDescriptor descriptor)
 		{
 			if (font is null)
-				throw new ArgumentNullException (nameof (font));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			var handle = CTFontCreateWithGraphicsFont2 (font.Handle, size, IntPtr.Zero, descriptor.GetHandle ());
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -2060,7 +2060,7 @@ namespace CoreText {
 		static IntPtr Create (CGFont font, nfloat size, CGAffineTransform transform)
 		{
 			if (font is null)
-				throw new ArgumentNullException (nameof (font));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			var handle = CTFontCreateWithGraphicsFont (font.Handle, size, ref transform, IntPtr.Zero);
 			if (handle == IntPtr.Zero)
 				throw ConstructorError.Unknown (typeof (CTFont));
@@ -2098,7 +2098,7 @@ namespace CoreText {
 		public CTFont? WithAttributes (nfloat size, CTFontDescriptor attributes)
 		{
 			if (attributes is null)
-				throw new ArgumentNullException (nameof (attributes));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (attributes));
 			return CreateFont (CTFontCreateCopyWithAttributes (Handle, size, IntPtr.Zero, attributes.Handle));
 		}
 
@@ -2137,7 +2137,7 @@ namespace CoreText {
 		public CTFont? WithFamily (nfloat size, string family)
 		{
 			if (family is null)
-				throw new ArgumentNullException (nameof (family));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (family));
 			var n = CFString.CreateNative (family);
 			try {
 				return CreateFont (CTFontCreateCopyWithFamily (Handle, size, IntPtr.Zero, n));
@@ -2151,7 +2151,7 @@ namespace CoreText {
 		public CTFont? WithFamily (nfloat size, string family, ref CGAffineTransform matrix)
 		{
 			if (family is null)
-				throw new ArgumentNullException (nameof (family));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (family));
 			var n = CFString.CreateNative (family);
 			try {
 				return CreateFont (CTFontCreateCopyWithFamily (Handle, size, ref matrix, n));
@@ -2173,7 +2173,7 @@ namespace CoreText {
 		public CTFont? ForString (string value, NSRange range)
 		{
 			if (value is null)
-				throw new ArgumentNullException (nameof (value));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (value));
 			var n = CFString.CreateNative (value);
 			try {
 				return CreateFont (CTFontCreateForString (Handle, n, range));
@@ -2214,7 +2214,7 @@ namespace CoreText {
 		public CTFont? ForString (string value, NSRange range, string? language)
 		{
 			if (value is null)
-				throw new ArgumentNullException (nameof (value));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (value));
 
 			var v = CFString.CreateNative (value);
 			var l = CFString.CreateNative (language);
@@ -2248,7 +2248,7 @@ namespace CoreText {
 		public NSObject? GetAttribute (NSString attribute)
 		{
 			if (attribute is null)
-				throw new ArgumentNullException (nameof (attribute));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (attribute));
 			return Runtime.GetNSObject (CTFontCopyAttribute (Handle, attribute.Handle));
 		}
 
@@ -2318,7 +2318,7 @@ namespace CoreText {
 		static extern IntPtr CTFontCopyName (IntPtr font, IntPtr nameKey);
 		public string? GetName (CTFontNameKey nameKey)
 		{
-			return CFString.FromHandle (CTFontCopyName (Handle, CTFontNameKeyId.ToId (nameKey).Handle), releaseHandle: true);
+			return CFString.FromHandle (CTFontCopyName (Handle, CTFontNameKeyId.ToId (nameKey).GetHandle ()), releaseHandle: true);
 		}
 
 		[DllImport (Constants.CoreTextLibrary)]
@@ -2332,7 +2332,7 @@ namespace CoreText {
 		public string? GetLocalizedName (CTFontNameKey nameKey, out string? actualLanguage)
 		{
 			IntPtr actual;
-			var ret = CFString.FromHandle (CTFontCopyLocalizedName (Handle, CTFontNameKeyId.ToId (nameKey).Handle, out actual), releaseHandle: true);
+			var ret = CFString.FromHandle (CTFontCopyLocalizedName (Handle, CTFontNameKeyId.ToId (nameKey).GetHandle (), out actual), releaseHandle: true);
 			actualLanguage = CFString.FromHandle (actual, releaseHandle: true);
 			return ret;
 		}
@@ -2429,7 +2429,7 @@ namespace CoreText {
 			if (canBeNull && array is null)
 				return;
 			if (array is null)
-				throw new ArgumentNullException (name);
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (name));
 			if (array.Length < count)
 				throw new ArgumentException (string.Format ("{0}.Length cannot be < count", name), name);
 		}
@@ -2517,7 +2517,7 @@ namespace CoreText {
 		public CGGlyph GetGlyphWithName (string glyphName)
 		{
 			if (glyphName is null)
-				throw new ArgumentNullException (nameof (glyphName));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (glyphName));
 			var nameHandle = CFString.CreateNative (glyphName);
 			try {
 				return CTFontGetGlyphWithName (Handle, nameHandle);
@@ -2552,7 +2552,7 @@ namespace CoreText {
 		public CGRect GetBoundingRects (CTFontOrientation orientation, CGGlyph[] glyphs)
 		{
 			if (glyphs is null)
-				throw new ArgumentNullException (nameof (glyphs));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (glyphs));
 			return GetBoundingRects (orientation, glyphs, null, glyphs.Length);
 		}
 
@@ -2570,7 +2570,7 @@ namespace CoreText {
 		public double GetAdvancesForGlyphs (CTFontOrientation orientation, CGGlyph[] glyphs)
 		{
 			if (glyphs is null)
-				throw new ArgumentNullException (nameof (glyphs));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (glyphs));
 			return GetAdvancesForGlyphs (orientation, glyphs, null, glyphs.Length);
 		}
 
@@ -2613,11 +2613,11 @@ namespace CoreText {
 		public void DrawGlyphs (CGContext context, CGGlyph [] glyphs, CGPoint [] positions)
 		{
 			if (context is null)
-				throw new ArgumentNullException (nameof (context));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (context));
 			if (glyphs is null)
-				throw new ArgumentNullException (nameof (glyphs));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (glyphs));
 			if (positions is null)
-				throw new ArgumentNullException (nameof (positions));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (positions));
 			int gl = glyphs.Length;
 			if (gl != positions.Length)
 				throw new ArgumentException ("array sizes fo context and glyphs differ");
@@ -2630,7 +2630,7 @@ namespace CoreText {
 		public nint GetLigatureCaretPositions (CGGlyph glyph, nfloat [] positions)
 		{
 			if (positions is null)
-				throw new ArgumentNullException (nameof (positions));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (positions));
 			return CTFontGetLigatureCaretPositions (Handle, glyph, positions, positions.Length);
 		}
 #endregion

src/CoreText/CTFontCollection.cs

@@ -51,11 +51,11 @@ namespace CoreText {
 
 #if !NET
 	public static class CTFontCollectionOptionKey {
-		public static readonly NSString RemoveDuplicates;
+		public static readonly NSString? RemoveDuplicates;
 
 		static CTFontCollectionOptionKey ()
 		{
-			RemoveDuplicates = Dlfcn.GetStringConstant (Libraries.CoreText.Handle, "kCTFontCollectionRemoveDuplicatesOption")!;
+			RemoveDuplicates = Dlfcn.GetStringConstant (Libraries.CoreText.Handle, "kCTFontCollectionRemoveDuplicatesOption");
 		}
 	}
 #endif
@@ -76,7 +76,7 @@ namespace CoreText {
 		public CTFontCollectionOptions (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -86,12 +86,16 @@ namespace CoreText {
 		// No mention of the expected type (int? NSNumber?)
 		public bool RemoveDuplicates {
 			get {
+				if (CTFontCollectionOptionKey.RemoveDuplicates is null)
+					return false;
 				var v = Adapter.GetInt32Value (Dictionary, CTFontCollectionOptionKey.RemoveDuplicates);
 				return v.HasValue ? v.Value != 0 : false;
 			}
 			set {
+				if (CTFontCollectionOptionKey.RemoveDuplicates is null)
+					throw new ArgumentOutOfRangeException (nameof (CTFontCollectionOptionKey.RemoveDuplicates));
 				var v = value ? (int?) 1 : null;
-				Adapter.SetValue (Dictionary, CTFontCollectionOptionKey.RemoveDuplicates, v);
+				Adapter.SetValue (Dictionary, CTFontCollectionOptionKey.RemoveDuplicates!, v);
 			}
 		}
 	}

src/CoreText/CTFontDescriptor.cs

@@ -87,54 +87,54 @@ namespace CoreText {
 	
 #if !NET
 	public static class CTFontDescriptorAttributeKey {
-		public static readonly NSString Url;
-		public static readonly NSString Name;
-		public static readonly NSString DisplayName;
-		public static readonly NSString FamilyName;
-		public static readonly NSString StyleName;
-		public static readonly NSString Traits;
-		public static readonly NSString Variation;
-		public static readonly NSString Size;
-		public static readonly NSString Matrix;
-		public static readonly NSString CascadeList;
-		public static readonly NSString CharacterSet;
-		public static readonly NSString Languages;
-		public static readonly NSString BaselineAdjust;
-		public static readonly NSString MacintoshEncodings;
-		public static readonly NSString Features;
-		public static readonly NSString FeatureSettings;
-		public static readonly NSString FixedAdvance;
-		public static readonly NSString FontOrientation;
-		public static readonly NSString FontFormat;
-		public static readonly NSString RegistrationScope;
-		public static readonly NSString Priority;
-		public static readonly NSString Enabled;
+		public static readonly NSString? Url;
+		public static readonly NSString? Name;
+		public static readonly NSString? DisplayName;
+		public static readonly NSString? FamilyName;
+		public static readonly NSString? StyleName;
+		public static readonly NSString? Traits;
+		public static readonly NSString? Variation;
+		public static readonly NSString? Size;
+		public static readonly NSString? Matrix;
+		public static readonly NSString? CascadeList;
+		public static readonly NSString? CharacterSet;
+		public static readonly NSString? Languages;
+		public static readonly NSString? BaselineAdjust;
+		public static readonly NSString? MacintoshEncodings;
+		public static readonly NSString? Features;
+		public static readonly NSString? FeatureSettings;
+		public static readonly NSString? FixedAdvance;
+		public static readonly NSString? FontOrientation;
+		public static readonly NSString? FontFormat;
+		public static readonly NSString? RegistrationScope;
+		public static readonly NSString? Priority;
+		public static readonly NSString? Enabled;
 
 		static CTFontDescriptorAttributeKey ()
 		{
 			var handle = Libraries.CoreText.Handle;
-			Url                 = Dlfcn.GetStringConstant (handle, "kCTFontURLAttribute")!;
-			Name                = Dlfcn.GetStringConstant (handle, "kCTFontNameAttribute")!;
-			DisplayName         = Dlfcn.GetStringConstant (handle, "kCTFontDisplayNameAttribute")!;
-			FamilyName          = Dlfcn.GetStringConstant (handle, "kCTFontFamilyNameAttribute")!;
-			StyleName           = Dlfcn.GetStringConstant (handle, "kCTFontStyleNameAttribute")!;
-			Traits              = Dlfcn.GetStringConstant (handle, "kCTFontTraitsAttribute")!;
-			Variation           = Dlfcn.GetStringConstant (handle, "kCTFontVariationAttribute")!;
-			Size                = Dlfcn.GetStringConstant (handle, "kCTFontSizeAttribute")!;
-			Matrix              = Dlfcn.GetStringConstant (handle, "kCTFontMatrixAttribute")!;
-			CascadeList         = Dlfcn.GetStringConstant (handle, "kCTFontCascadeListAttribute")!;
-			CharacterSet        = Dlfcn.GetStringConstant (handle, "kCTFontCharacterSetAttribute")!;
-			Languages           = Dlfcn.GetStringConstant (handle, "kCTFontLanguagesAttribute")!;
-			BaselineAdjust      = Dlfcn.GetStringConstant (handle, "kCTFontBaselineAdjustAttribute")!;
-			MacintoshEncodings  = Dlfcn.GetStringConstant (handle, "kCTFontMacintoshEncodingsAttribute")!;
-			Features            = Dlfcn.GetStringConstant (handle, "kCTFontFeaturesAttribute")!;
-			FeatureSettings     = Dlfcn.GetStringConstant (handle, "kCTFontFeatureSettingsAttribute")!;
-			FixedAdvance        = Dlfcn.GetStringConstant (handle, "kCTFontFixedAdvanceAttribute")!;
-			FontOrientation     = Dlfcn.GetStringConstant (handle, "kCTFontOrientationAttribute")!;
-			FontFormat          = Dlfcn.GetStringConstant (handle, "kCTFontFormatAttribute")!;
-			RegistrationScope   = Dlfcn.GetStringConstant (handle, "kCTFontRegistrationScopeAttribute")!;
-			Priority            = Dlfcn.GetStringConstant (handle, "kCTFontPriorityAttribute")!;
-			Enabled             = Dlfcn.GetStringConstant (handle, "kCTFontEnabledAttribute")!;
+			Url                 = Dlfcn.GetStringConstant (handle, "kCTFontURLAttribute");
+			Name                = Dlfcn.GetStringConstant (handle, "kCTFontNameAttribute");
+			DisplayName         = Dlfcn.GetStringConstant (handle, "kCTFontDisplayNameAttribute");
+			FamilyName          = Dlfcn.GetStringConstant (handle, "kCTFontFamilyNameAttribute");
+			StyleName           = Dlfcn.GetStringConstant (handle, "kCTFontStyleNameAttribute");
+			Traits              = Dlfcn.GetStringConstant (handle, "kCTFontTraitsAttribute");
+			Variation           = Dlfcn.GetStringConstant (handle, "kCTFontVariationAttribute");
+			Size                = Dlfcn.GetStringConstant (handle, "kCTFontSizeAttribute");
+			Matrix              = Dlfcn.GetStringConstant (handle, "kCTFontMatrixAttribute");
+			CascadeList         = Dlfcn.GetStringConstant (handle, "kCTFontCascadeListAttribute");
+			CharacterSet        = Dlfcn.GetStringConstant (handle, "kCTFontCharacterSetAttribute");
+			Languages           = Dlfcn.GetStringConstant (handle, "kCTFontLanguagesAttribute");
+			BaselineAdjust      = Dlfcn.GetStringConstant (handle, "kCTFontBaselineAdjustAttribute");
+			MacintoshEncodings  = Dlfcn.GetStringConstant (handle, "kCTFontMacintoshEncodingsAttribute");
+			Features            = Dlfcn.GetStringConstant (handle, "kCTFontFeaturesAttribute");
+			FeatureSettings     = Dlfcn.GetStringConstant (handle, "kCTFontFeatureSettingsAttribute");
+			FixedAdvance        = Dlfcn.GetStringConstant (handle, "kCTFontFixedAdvanceAttribute");
+			FontOrientation     = Dlfcn.GetStringConstant (handle, "kCTFontOrientationAttribute");
+			FontFormat          = Dlfcn.GetStringConstant (handle, "kCTFontFormatAttribute");
+			RegistrationScope   = Dlfcn.GetStringConstant (handle, "kCTFontRegistrationScopeAttribute");
+			Priority            = Dlfcn.GetStringConstant (handle, "kCTFontPriorityAttribute");
+			Enabled             = Dlfcn.GetStringConstant (handle, "kCTFontEnabledAttribute");
 		}
 	}
 #endif // !NET
@@ -155,7 +155,7 @@ namespace CoreText {
 		public CTFontDescriptorAttributes (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -163,135 +163,148 @@ namespace CoreText {
 
 		public NSUrl Url {
 			get {return (NSUrl) Dictionary [CTFontDescriptorAttributeKey.Url];}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Url, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Url!, value);}
 		}
 
-		public string Name {
+		public string? Name {
 			get {return Adapter.GetStringValue (Dictionary, CTFontDescriptorAttributeKey.Name);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Name, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Name!, value);}
 		}
 
-		public string DisplayName {
+		public string? DisplayName {
 			get {return Adapter.GetStringValue (Dictionary, CTFontDescriptorAttributeKey.DisplayName);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.DisplayName, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.DisplayName!, value);}
 		}
 
-		public string FamilyName {
+		public string? FamilyName {
 			get {return Adapter.GetStringValue (Dictionary, CTFontDescriptorAttributeKey.FamilyName);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FamilyName, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FamilyName!, value);}
 		}
 
-		public string StyleName {
+		public string? StyleName {
 			get {return Adapter.GetStringValue (Dictionary, CTFontDescriptorAttributeKey.StyleName);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.StyleName, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.StyleName!, value);}
 		}
 
 		public CTFontTraits? Traits {
 			get {
-				var traits = (NSDictionary) Dictionary [CTFontDescriptorAttributeKey.Traits];
-				if (traits is null)
-					return null;
-				return new CTFontTraits (traits);
+				if (CTFontDescriptorAttributeKey.Traits is NSString traitsKey && Dictionary[traitsKey] is NSDictionary traits)
+					return new CTFontTraits (traits);
+				return null;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Traits, value?.Dictionary);
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Traits!, value?.Dictionary);
 			}
 		}
 
 		public CTFontVariation? Variation {
 			get {
-				var variation = (NSDictionary) Dictionary [CTFontDescriptorAttributeKey.Variation];
-				return variation is null ? null : new CTFontVariation (variation);
+				if (CTFontDescriptorAttributeKey.Variation is NSString variationKey && Dictionary[variationKey] is NSDictionary variation)
+					return new CTFontVariation (variation);
+				return null;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Variation, value?.Dictionary);
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Variation!, value?.Dictionary);
 			}
 		}
 
 		// CFNumber
 		public float? Size {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontDescriptorAttributeKey.Size);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Size, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Size!, value);}
 		}
 
 		public unsafe CGAffineTransform? Matrix {
 			get {
-				var d = (NSData) Dictionary [CTFontDescriptorAttributeKey.Matrix];
-				if (d == null)
-					return null;
-				return Marshal.PtrToStructure<CGAffineTransform> (d.Bytes);
+				if (CTFontDescriptorAttributeKey.Matrix is NSString matrixKey && Dictionary[matrixKey] is NSData d)
+					return Marshal.PtrToStructure<CGAffineTransform> (d.Bytes);
+				return null;
 			}
 			set {
+				if (CTFontDescriptorAttributeKey.Matrix is null)
+					throw new ArgumentOutOfRangeException (nameof (CTFontDescriptorAttributeKey.Matrix));
 				if (!value.HasValue)
-					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Matrix, (NSObject?) null);
+					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Matrix!, (NSObject?) null);
 				else {
 					byte[] data = new byte [sizeof (CGAffineTransform)];
 					fixed (byte* p = data) {
 						Marshal.StructureToPtr (value.Value, (IntPtr) p, false);
 					}
-					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Matrix, NSData.FromArray (data));
+					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Matrix!, NSData.FromArray (data));
 				}
 			}
 		}
 
-		public IEnumerable<CTFontDescriptor> CascadeList {
+		public IEnumerable<CTFontDescriptor>? CascadeList {
 			get {
-				return Adapter.GetNativeArray (Dictionary, CTFontDescriptorAttributeKey.CascadeList,
-						d => new CTFontDescriptor (d, false));
+				if (CTFontDescriptorAttributeKey.CascadeList is NSString cascadeList)
+					return Adapter.GetNativeArray (Dictionary, cascadeList, d => new CTFontDescriptor (d, false));
+				return null;
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTFontDescriptorAttributeKey.CascadeList, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTFontDescriptorAttributeKey.CascadeList!, value);}
 		}
 
 		public NSCharacterSet CharacterSet {
 			get {return (NSCharacterSet) Dictionary [CTFontDescriptorAttributeKey.CharacterSet];}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.CharacterSet, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.CharacterSet!, value);}
 		}
 
-		public IEnumerable<string> Languages {
+		public IEnumerable<string>? Languages {
 			get {return Adapter.GetStringArray (Dictionary, CTFontDescriptorAttributeKey.Languages);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Languages, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Languages!, value);}
 		}
 
 		// float represented as a CFNumber
 		public float? BaselineAdjust {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontDescriptorAttributeKey.BaselineAdjust);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.BaselineAdjust, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.BaselineAdjust!, value);}
 		}
 
 		public float? MacintoshEncodings {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontDescriptorAttributeKey.MacintoshEncodings);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.MacintoshEncodings, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.MacintoshEncodings!, value);}
 		}
 
-		public IEnumerable<CTFontFeatures> Features {
+		public IEnumerable<CTFontFeatures>? Features {
 			get {
-				return Adapter.GetNativeArray (Dictionary, CTFontDescriptorAttributeKey.Features,
+				if (CTFontDescriptorAttributeKey.Features is NSString features) {
+					return Adapter.GetNativeArray (Dictionary, features,
 						d => new CTFontFeatures ((NSDictionary) Runtime.GetNSObject (d)!));
+				}
+				return null;
 			}
 			set {
+				if (CTFontDescriptorAttributeKey.Features is null)
+					throw new ArgumentOutOfRangeException (nameof (CTFontDescriptorAttributeKey.Features));
+
 				List<CTFontFeatures> v;
 				if (value is null || (v = new List<CTFontFeatures> (value)).Count == 0) {
-					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Features, (NSObject?) null);
+					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Features!, (NSObject?) null);
 					return;
 				}
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Features,
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Features!,
 						NSArray.FromNSObjects ((IList<NSObject>) v.ConvertAll (e => (NSObject) e.Dictionary)));
 			}
 		}
 
-		public IEnumerable<CTFontFeatureSettings> FeatureSettings {
+		public IEnumerable<CTFontFeatureSettings>? FeatureSettings {
 			get {
-				return Adapter.GetNativeArray (Dictionary, CTFontDescriptorAttributeKey.Features,
+				if (CTFontDescriptorAttributeKey.Features is NSString features) {
+					return Adapter.GetNativeArray (Dictionary, CTFontDescriptorAttributeKey.Features,
 						d => new CTFontFeatureSettings ((NSDictionary) Runtime.GetNSObject (d)!));
+				}
+				return null;
 			}
 			set {
+				if (CTFontDescriptorAttributeKey.Features is null)
+					throw new ArgumentOutOfRangeException (nameof (CTFontDescriptorAttributeKey.Features));
 				List<CTFontFeatureSettings> v;
 				if (value is null || (v = new List<CTFontFeatureSettings> (value)).Count == 0) {
-					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Features, (NSObject?) null);
+					Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Features!, (NSObject?) null);
 					return;
 				}
 
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FeatureSettings,
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FeatureSettings!,
 						NSArray.FromNSObjects ((IList<NSObject>) v.ConvertAll (e => (NSObject) e.Dictionary)));
 			}
 		}
@@ -299,49 +312,61 @@ namespace CoreText {
 		// CFNumber
 		public float? FixedAdvance {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontDescriptorAttributeKey.FixedAdvance);}
-			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FixedAdvance, value);}
+			set {Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FixedAdvance!, value);}
 		}
 
 		public CTFontOrientation? FontOrientation {
 			get {
-				var value = Adapter.GetUInt32Value (Dictionary, CTFontDescriptorAttributeKey.FontOrientation);
-				return !value.HasValue ? null : (CTFontOrientation?) value.Value;
+				if (CTFontDescriptorAttributeKey.FontOrientation is NSString fontOrientation) {
+					var value = Adapter.GetUInt32Value (Dictionary, fontOrientation);
+					return !value.HasValue ? null : (CTFontOrientation?) value.Value;
+				}
+				return null;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FontOrientation, 
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FontOrientation!, 
 						value.HasValue ? (uint?) value.Value : null);
 			}
 		}
 
 		public CTFontFormat? FontFormat {
 			get {
-				var value = Adapter.GetUInt32Value (Dictionary, CTFontDescriptorAttributeKey.FontFormat);
-				return !value.HasValue ? null : (CTFontFormat?) value.Value;
+				if (CTFontDescriptorAttributeKey.FontFormat is NSString fontFormat) {
+					var value = Adapter.GetUInt32Value (Dictionary, fontFormat);
+					return !value.HasValue ? null : (CTFontFormat?) value.Value;
+				}
+				return null;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FontFormat, 
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.FontFormat!, 
 						value.HasValue ? (uint?) value.Value : null);
 			}
 		}
 
 		public CTFontManagerScope? RegistrationScope {
 			get {
-				var value = Adapter.GetUnsignedIntegerValue (Dictionary, CTFontDescriptorAttributeKey.RegistrationScope);
-				return !value.HasValue ? null : (CTFontManagerScope?) (ulong) value.Value;
+				if (CTFontDescriptorAttributeKey.RegistrationScope is NSString registrationScope) {
+					var value = Adapter.GetUnsignedIntegerValue (Dictionary, registrationScope);
+					return !value.HasValue ? null : (CTFontManagerScope?) (ulong) value.Value;
+				}
+				return null;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.RegistrationScope,
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.RegistrationScope!,
 				value.HasValue ? (nuint?) (ulong) value.Value : null);
 			}
 		}
 
 		public CTFontPriority? Priority {
 			get {
-				var value = Adapter.GetUInt32Value (Dictionary, CTFontDescriptorAttributeKey.Priority);
-				return !value.HasValue ? null : (CTFontPriority?) value.Value;
+				if (CTFontDescriptorAttributeKey.Priority is NSString priority) {
+					var value = Adapter.GetUInt32Value (Dictionary, priority);
+					return !value.HasValue ? null : (CTFontPriority?) value.Value;
+				}
+				return null;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Priority, 
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Priority!, 
 						value.HasValue ? (uint?) value.Value : null);
 			}
 		}
@@ -354,8 +379,7 @@ namespace CoreText {
 				return value.Int32Value != 0;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Enabled, 
-						value ? new NSNumber (1) : null);
+				Adapter.SetValue (Dictionary, CTFontDescriptorAttributeKey.Enabled!, value ? new NSNumber (1) : null);
 			}
 		}
 	}
@@ -379,7 +403,7 @@ namespace CoreText {
 		static IntPtr Create (string name, nfloat size)
 		{
 			if (name is null)
-				throw new ArgumentNullException (nameof (name));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (name));
 			var nameHandle = CFString.CreateNative (name);
 			try {
 				return CTFontDescriptorCreateWithNameAndSize (nameHandle, size);
@@ -405,7 +429,7 @@ namespace CoreText {
 		public CTFontDescriptor? WithAttributes (NSDictionary attributes)
 		{
 			if (attributes is null)
-				throw new ArgumentNullException (nameof (attributes));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (attributes));
 			return CreateDescriptor (CTFontDescriptorCreateCopyWithAttributes (Handle, attributes.Handle));
 		}
 
@@ -418,8 +442,8 @@ namespace CoreText {
 
 		public CTFontDescriptor? WithAttributes (CTFontDescriptorAttributes attributes)
 		{
-			if (attributes == null)
-				throw new ArgumentNullException (nameof (attributes));
+			if (attributes is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (attributes));
 			return CreateDescriptor (CTFontDescriptorCreateCopyWithAttributes (Handle, attributes.Dictionary.Handle));
 		}
 
@@ -688,7 +712,7 @@ namespace CoreText {
 		public NSObject? GetAttribute (NSString attribute)
 		{
 			if (attribute is null)
-				throw new ArgumentNullException (nameof (attribute));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (attribute));
 			return Runtime.GetNSObject<NSObject> (CTFontDescriptorCopyAttribute (Handle, attribute.Handle), true);
 		}
 
@@ -734,7 +758,7 @@ namespace CoreText {
 			// FIXME: the P/Invoke used below is wrong, it expects a block, not a function pointer.
 			// throwing a NIE instead of crashing until this is implemented properly.
 			throw new NotImplementedException ();
-//			var ma = mandatoryAttributes == null ? IntPtr.Zero : mandatoryAttributes.Handle;
+//			var ma = mandatoryAttributes is null ? IntPtr.Zero : mandatoryAttributes.Handle;
 //			// FIXME: SIGSEGV probably due to mandatoryAttributes mismatch
 //			using (var ar = CFArray.FromNativeObjects (descriptors)) {
 //				return CTFontDescriptorMatchFontDescriptorsWithProgressHandler (ar.Handle, ma, progressHandler);

src/CoreText/CTFontManager.cs

@@ -27,6 +27,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
@@ -112,8 +115,8 @@ namespace CoreText {
 #endif
 		public static bool IsFontSupported (NSUrl url)
 		{
-			if (url == null)
-				throw new ArgumentNullException ("url");
+			if (url is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (url));
 			return CTFontManagerIsSupportedFont (url.Handle);
 		}
 #elif !XAMCORE_3_0
@@ -130,8 +133,8 @@ namespace CoreText {
 		[Obsolete ("API not available on iOS, it will always return false.")]
 		public static bool IsFontSupported (NSUrl url)
 		{
-			if (url == null)
-				throw new ArgumentNullException ("url");
+			if (url is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (url));
 			return false;
 		}
 #endif
@@ -139,10 +142,10 @@ namespace CoreText {
 		[DllImport (Constants.CoreTextLibrary)]
 		[return: MarshalAs (UnmanagedType.I1)]
 		static extern bool CTFontManagerRegisterFontsForURL (IntPtr fontUrl, CTFontManagerScope scope, ref IntPtr error);
-		public static NSError RegisterFontsForUrl (NSUrl fontUrl, CTFontManagerScope scope)
+		public static NSError? RegisterFontsForUrl (NSUrl fontUrl, CTFontManagerScope scope)
 		{
-			if (fontUrl == null)
-				throw new ArgumentNullException ("fontUrl");
+			if (fontUrl is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (fontUrl));
 			
 			IntPtr error = IntPtr.Zero;
 
@@ -159,17 +162,17 @@ namespace CoreText {
 
 		static NSArray EnsureNonNullArray (object [] items, string name)
 		{
-			if (items == null)
-				throw new ArgumentNullException (name);
+			if (items is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (name));
 
 			foreach (var i in items)
-				if (i == null)
+				if (i is null)
 					throw new ArgumentException ("Array contains a null entry", name);
 
 			return NSArray.FromObjects (items);
 		}
 
-		static T[] ArrayFromHandle<T> (IntPtr handle, bool releaseAfterUse) where T : class, INativeObject
+		static T[]? ArrayFromHandle<T> (IntPtr handle, bool releaseAfterUse) where T : class, INativeObject
 		{
 			if (handle == IntPtr.Zero)
 				return null;
@@ -228,7 +231,7 @@ namespace CoreText {
 		[Deprecated (PlatformName.WatchOS, 6,0, message: "Use 'RegisterFonts' instead.")]
 		[Deprecated (PlatformName.TvOS, 13,0, message: "Use 'RegisterFonts' instead.")]
 #endif
-		public static NSError [] RegisterFontsForUrl (NSUrl [] fontUrls, CTFontManagerScope scope)
+		public static NSError []? RegisterFontsForUrl (NSUrl [] fontUrls, CTFontManagerScope scope)
 		{
 			using (var arr = EnsureNonNullArray (fontUrls, nameof (fontUrls))) {
 				IntPtr error_array = IntPtr.Zero;
@@ -258,7 +261,7 @@ namespace CoreText {
 		static unsafe bool TrampolineRegistrationHandler (IntPtr block, /* NSArray */ IntPtr errors, bool done)
 		{
 			var del = BlockLiteral.GetTarget<CTFontRegistrationHandler> (block);
-			return del != null ? del (NSArray.ArrayFromHandle<NSError> (errors), done) : true;
+			return del is not null ? del (NSArray.ArrayFromHandle<NSError> (errors), done) : true;
 		}
 
 #if NET
@@ -304,7 +307,7 @@ namespace CoreText {
 		public static void RegisterFonts (NSUrl [] fontUrls, CTFontManagerScope scope, bool enabled, CTFontRegistrationHandler registrationHandler)
 		{
 			using (var arr = EnsureNonNullArray (fontUrls, nameof (fontUrls))) {
-				if (registrationHandler == null) {
+				if (registrationHandler is null) {
 					CTFontManagerRegisterFontURLs (arr.Handle, scope, enabled, IntPtr.Zero);
 				} else {
 					BlockLiteral block_handler = new BlockLiteral ();
@@ -319,10 +322,10 @@ namespace CoreText {
 		[return: MarshalAs (UnmanagedType.I1)]
 		static extern bool CTFontManagerUnregisterFontsForURL(IntPtr fotUrl, CTFontManagerScope scope, ref IntPtr error);
 
-		public static NSError UnregisterFontsForUrl (NSUrl fontUrl, CTFontManagerScope scope)
+		public static NSError? UnregisterFontsForUrl (NSUrl fontUrl, CTFontManagerScope scope)
 		{
-			if (fontUrl == null)
-				throw new ArgumentNullException ("fontUrl");
+			if (fontUrl is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (fontUrl));
 
 			IntPtr error = IntPtr.Zero;
 
@@ -383,7 +386,7 @@ namespace CoreText {
 		[Deprecated (PlatformName.WatchOS, 6,0, message : "Use 'UnregisterFonts' instead.")]
 		[Deprecated (PlatformName.TvOS, 13,0, message : "Use 'UnregisterFonts' instead.")]
 #endif
-		public static NSError [] UnregisterFontsForUrl (NSUrl [] fontUrls, CTFontManagerScope scope)
+		public static NSError []? UnregisterFontsForUrl (NSUrl [] fontUrls, CTFontManagerScope scope)
 		{
 			IntPtr error_array = IntPtr.Zero;
 			using (var arr = EnsureNonNullArray (fontUrls, nameof (fontUrls))) {
@@ -436,7 +439,7 @@ namespace CoreText {
 		public static void UnregisterFonts (NSUrl [] fontUrls, CTFontManagerScope scope, CTFontRegistrationHandler registrationHandler)
 		{
 			using (var arr = EnsureNonNullArray (fontUrls, nameof (fontUrls))) {
-				if (registrationHandler == null) {
+				if (registrationHandler is null) {
 					CTFontManagerUnregisterFontURLs (arr.Handle, scope, IntPtr.Zero);
 				} else {
 					BlockLiteral block_handler = new BlockLiteral ();
@@ -468,8 +471,8 @@ namespace CoreText {
 #endif
 		public static CTFontDescriptor[] GetFonts (NSUrl url)
 		{
-			if (url == null)
-				throw new ArgumentNullException ("url");
+			if (url is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (url));
 
 			var arrayPtr = CTFontManagerCreateFontDescriptorsFromURL (url.Handle);
 			if (arrayPtr == IntPtr.Zero)
@@ -488,10 +491,10 @@ namespace CoreText {
 		[return: MarshalAs (UnmanagedType.I1)]
 		static extern bool CTFontManagerRegisterGraphicsFont (IntPtr cgfont, out IntPtr error);
 
-		public static bool RegisterGraphicsFont (CGFont font, out NSError error)
+		public static bool RegisterGraphicsFont (CGFont font, out NSError? error)
 		{
-			if (font == null)
-				throw new ArgumentNullException ("font");
+			if (font is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			IntPtr h = IntPtr.Zero;
 			bool ret;
 			try {
@@ -511,10 +514,10 @@ namespace CoreText {
 		[return: MarshalAs (UnmanagedType.I1)]
 		static extern bool CTFontManagerUnregisterGraphicsFont (IntPtr cgfont, out IntPtr error);
 
-		public static bool UnregisterGraphicsFont (CGFont font, out NSError error)
+		public static bool UnregisterGraphicsFont (CGFont font, out NSError? error)
 		{
-			if (font == null)
-				throw new ArgumentNullException ("font");
+			if (font is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			IntPtr h = IntPtr.Zero;
 			bool ret;
 			try {
@@ -537,11 +540,13 @@ namespace CoreText {
 #if !XAMCORE_3_0
 			ErrorDomain  = Dlfcn.GetStringConstant (handle, "kCTFontManagerErrorDomain");
 #endif
+#pragma warning disable CS0618 // Type or member is obsolete
 			ErrorFontUrlsKey  = Dlfcn.GetStringConstant (handle, "kCTFontManagerErrorFontURLsKey");
+#pragma warning restore CS0618 // Type or member is obsolete
 		}
 #endif // !NET
 
-		static NSString _RegisteredFontsChangedNotification;
+		static NSString? _RegisteredFontsChangedNotification;
 
 #if NET
 		[SupportedOSPlatform ("ios7.0")]
@@ -551,20 +556,20 @@ namespace CoreText {
 #else
 		[iOS (7,0)]
 #endif
-		static NSString RegisteredFontsChangedNotification {
+		static NSString? RegisteredFontsChangedNotification {
 			get {
-				if (_RegisteredFontsChangedNotification == null)
+				if (_RegisteredFontsChangedNotification is null)
 					_RegisteredFontsChangedNotification = Dlfcn.GetStringConstant (Libraries.CoreText.Handle, "kCTFontManagerRegisteredFontsChangedNotification");
 				return _RegisteredFontsChangedNotification;
 			}
 		}
 
 #if !XAMCORE_3_0
-		public readonly static NSString ErrorDomain;
+		public readonly static NSString? ErrorDomain;
 #endif
 #if !NET
 		[Obsolete ("Use the 'CTFontManagerErrorKeys.FontUrlsKey' property instead.")]
-		public readonly static NSString ErrorFontUrlsKey;
+		public readonly static NSString? ErrorFontUrlsKey;
 #endif
 
 		public static partial class Notifications {
@@ -618,7 +623,7 @@ namespace CoreText {
 		public static void RegisterFontDescriptors (CTFontDescriptor[] fontDescriptors, CTFontManagerScope scope, bool enabled, CTFontRegistrationHandler registrationHandler)
 		{
 			using (var arr = EnsureNonNullArray (fontDescriptors, nameof (fontDescriptors))) {
-				if (registrationHandler == null) {
+				if (registrationHandler is null) {
 					CTFontManagerRegisterFontDescriptors (arr.Handle, scope, enabled, IntPtr.Zero);
 				} else {
 					BlockLiteral block_handler = new BlockLiteral ();
@@ -672,7 +677,7 @@ namespace CoreText {
 		public static void UnregisterFontDescriptors (CTFontDescriptor[] fontDescriptors, CTFontManagerScope scope, CTFontRegistrationHandler registrationHandler)
 		{
 			using (var arr = EnsureNonNullArray (fontDescriptors, nameof (fontDescriptors))) {
-				if (registrationHandler == null) {
+				if (registrationHandler is null) {
 					CTFontManagerUnregisterFontDescriptors (arr.Handle, scope, IntPtr.Zero);
 				} else {
 					BlockLiteral block_handler = new BlockLiteral ();
@@ -706,7 +711,7 @@ namespace CoreText {
 		[NoTV]
 		[NoMac]
 #endif
-		public static CTFontDescriptor[] GetRegisteredFontDescriptors (CTFontManagerScope scope, bool enabled)
+		public static CTFontDescriptor[]? GetRegisteredFontDescriptors (CTFontManagerScope scope, bool enabled)
 		{
 			var p = CTFontManagerCopyRegisteredFontDescriptors (scope, enabled);
 			// Copy/Create rule - we must release the CFArrayRef
@@ -718,10 +723,10 @@ namespace CoreText {
 		[DllImport (Constants.CoreTextLibrary)]
 		static extern unsafe /* CTFontDescriptorRef _Nullable */ IntPtr CTFontManagerCreateFontDescriptorFromData (/* CFDataRef */ IntPtr data);
 
-		public static CTFontDescriptor CreateFontDescriptor (NSData data)
+		public static CTFontDescriptor? CreateFontDescriptor (NSData data)
 		{
-			if (data == null)
-				throw new ArgumentNullException (nameof (data));
+			if (data is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (data));
 
 			var p = CTFontManagerCreateFontDescriptorFromData (data.Handle);
 			if (p == IntPtr.Zero)
@@ -755,10 +760,10 @@ namespace CoreText {
 		[Mac (10,15)]
 		[iOS (13,0)]
 #endif
-		public static CTFontDescriptor[] CreateFontDescriptors (NSData data)
+		public static CTFontDescriptor[]? CreateFontDescriptors (NSData data)
 		{
-			if (data == null)
-				throw new ArgumentNullException (nameof (data));
+			if (data is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (data));
 
 			var p = CTFontManagerCreateFontDescriptorsFromData (data.Handle);
 			// Copy/Create rule - we must release the CFArrayRef
@@ -810,7 +815,7 @@ namespace CoreText {
 		public static void RegisterFonts (string[] assetNames, CFBundle bundle, CTFontManagerScope scope, bool enabled, CTFontRegistrationHandler registrationHandler)
 		{
 			using (var arr = EnsureNonNullArray (assetNames, nameof (assetNames))) {
-				if (registrationHandler == null) {
+				if (registrationHandler is null) {
 					CTFontManagerRegisterFontsWithAssetNames (arr.Handle, bundle.GetHandle (), scope, enabled, IntPtr.Zero);
 				} else {
 					BlockLiteral block_handler = new BlockLiteral ();
@@ -855,7 +860,7 @@ namespace CoreText {
 		static unsafe void TrampolineRequestFonts (IntPtr block, /* CFArray */ IntPtr fontDescriptors)
 		{
 			var del = BlockLiteral.GetTarget<CTFontManagerRequestFontsHandler> (block);
-			if (del != null)
+			if (del is not null)
 				del (NSArray.ArrayFromHandle<CTFontDescriptor> (fontDescriptors));
 		}
 
@@ -873,8 +878,8 @@ namespace CoreText {
 		[BindingImpl (BindingImplOptions.Optimizable)]
 		public static void RequestFonts (CTFontDescriptor[] fontDescriptors, CTFontManagerRequestFontsHandler completionHandler)
 		{
-			if (completionHandler == null)
-				throw new ArgumentNullException (nameof (completionHandler));
+			if (completionHandler is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (completionHandler));
 
 			using (var arr = EnsureNonNullArray (fontDescriptors, nameof (fontDescriptors))) {
 				BlockLiteral block_handler = new BlockLiteral ();

src/CoreText/CTFontNameKey.cs

@@ -26,6 +26,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 
@@ -58,24 +61,24 @@ namespace CoreText {
 
 	static partial class CTFontNameKeyId {
 #if !NET
-		public static readonly NSString Copyright;
-		public static readonly NSString Family;
-		public static readonly NSString SubFamily;
-		public static readonly NSString Style;
-		public static readonly NSString Unique;
-		public static readonly NSString Full;
-		public static readonly NSString Version;
-		public static readonly NSString PostScript;
-		public static readonly NSString Trademark;
-		public static readonly NSString Manufacturer;
-		public static readonly NSString Designer;
-		public static readonly NSString Description;
-		public static readonly NSString VendorUrl;
-		public static readonly NSString DesignerUrl;
-		public static readonly NSString License;
-		public static readonly NSString LicenseUrl;
-		public static readonly NSString SampleText;
-		public static readonly NSString PostscriptCid;
+		public static readonly NSString? Copyright;
+		public static readonly NSString? Family;
+		public static readonly NSString? SubFamily;
+		public static readonly NSString? Style;
+		public static readonly NSString? Unique;
+		public static readonly NSString? Full;
+		public static readonly NSString? Version;
+		public static readonly NSString? PostScript;
+		public static readonly NSString? Trademark;
+		public static readonly NSString? Manufacturer;
+		public static readonly NSString? Designer;
+		public static readonly NSString? Description;
+		public static readonly NSString? VendorUrl;
+		public static readonly NSString? DesignerUrl;
+		public static readonly NSString? License;
+		public static readonly NSString? LicenseUrl;
+		public static readonly NSString? SampleText;
+		public static readonly NSString? PostscriptCid;
 
 		static CTFontNameKeyId ()
 		{
@@ -101,7 +104,7 @@ namespace CoreText {
 		}
 #endif
 
-		public static NSString ToId (CTFontNameKey key)
+		public static NSString? ToId (CTFontNameKey key)
 		{
 			switch (key) {
 				case CTFontNameKey.Copyright:     return Copyright;
@@ -128,7 +131,10 @@ namespace CoreText {
 
 		public static CTFontNameKey ToFontNameKey (NSString key)
 		{
-			if (key == Copyright)    	return CTFontNameKey.Copyright;
+			if (key is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (key));
+
+			if (key == Copyright)     return CTFontNameKey.Copyright;
 			if (key == Family)        return CTFontNameKey.Family;
 			if (key == SubFamily)     return CTFontNameKey.SubFamily;
 			if (key == Style)         return CTFontNameKey.Style;

src/CoreText/CTFontTrait.cs

@@ -26,6 +26,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 
@@ -38,10 +41,10 @@ namespace CoreText {
 
 #if !NET
 	public static class CTFontTraitKey {
-		public static readonly NSString Symbolic;
-		public static readonly NSString Weight;
-		public static readonly NSString Width;
-		public static readonly NSString Slant;
+		public static readonly NSString? Symbolic;
+		public static readonly NSString? Weight;
+		public static readonly NSString? Width;
+		public static readonly NSString? Slant;
 
 		static CTFontTraitKey ()
 		{
@@ -102,8 +105,8 @@ namespace CoreText {
 
 		public CTFontTraits (NSDictionary dictionary)
 		{
-			if (dictionary == null)
-				throw new ArgumentNullException ("dictionary");
+			if (dictionary is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -112,7 +115,7 @@ namespace CoreText {
 		// CFNumber
 		public uint? Symbolic {
 			get {return Adapter.GetUInt32Value (Dictionary, CTFontTraitKey.Symbolic);}
-			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Symbolic, value);}
+			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Symbolic!, value);}
 		}
 
 		public CTFontSymbolicTraits? SymbolicTraits {
@@ -144,19 +147,19 @@ namespace CoreText {
 		// CFNumber representing a float value 
 		public float? Weight {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontTraitKey.Weight);}
-			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Weight, value);}
+			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Weight!, value);}
 		}
 
 		// CFNumber representing a float value 
 		public float? Width {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontTraitKey.Width);}
-			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Width, value);}
+			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Width!, value);}
 		}
 
 		// CFNumber representing a float value 
 		public float? Slant {
 			get {return Adapter.GetSingleValue (Dictionary, CTFontTraitKey.Slant);}
-			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Slant, value);}
+			set {Adapter.SetValue (Dictionary, CTFontTraitKey.Slant!, value);}
 		}
 
 		internal const int  ClassMaskShift      = 28;

src/CoreText/CTFrame.cs

@@ -58,21 +58,21 @@ namespace CoreText {
 #if !NET
 	public static class CTFrameAttributeKey {
 
-		public static readonly NSString Progression;
+		public static readonly NSString? Progression;
 
-		public static readonly NSString PathFillRule;
-		public static readonly NSString PathWidth;
-		public static readonly NSString ClippingPaths;
-		public static readonly NSString PathClippingPath;
+		public static readonly NSString? PathFillRule;
+		public static readonly NSString? PathWidth;
+		public static readonly NSString? ClippingPaths;
+		public static readonly NSString? PathClippingPath;
 		
 		static CTFrameAttributeKey ()
 		{
 			var handle = Libraries.CoreText.Handle;
-			Progression = Dlfcn.GetStringConstant (handle, "kCTFrameProgressionAttributeName")!;
-			PathFillRule = Dlfcn.GetStringConstant (handle, "kCTFramePathFillRuleAttributeName")!;
-			PathWidth = Dlfcn.GetStringConstant (handle, "kCTFramePathWidthAttributeName")!;
-			ClippingPaths = Dlfcn.GetStringConstant (handle, "kCTFrameClippingPathsAttributeName")!;
-			PathClippingPath = Dlfcn.GetStringConstant (handle, "kCTFramePathClippingPathAttributeName")!;
+			Progression = Dlfcn.GetStringConstant (handle, "kCTFrameProgressionAttributeName");
+			PathFillRule = Dlfcn.GetStringConstant (handle, "kCTFramePathFillRuleAttributeName");
+			PathWidth = Dlfcn.GetStringConstant (handle, "kCTFramePathWidthAttributeName");
+			ClippingPaths = Dlfcn.GetStringConstant (handle, "kCTFrameClippingPathsAttributeName");
+			PathClippingPath = Dlfcn.GetStringConstant (handle, "kCTFramePathClippingPathAttributeName");
 		}
 	}
 #endif
@@ -93,7 +93,7 @@ namespace CoreText {
 		public CTFrameAttributes (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
@@ -105,7 +105,7 @@ namespace CoreText {
 				return !value.HasValue ? null : (CTFrameProgression?) value.Value;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTFrameAttributeKey.Progression,
+				Adapter.SetValue (Dictionary, CTFrameAttributeKey.Progression!,
 						value.HasValue ? (uint?) value.Value : null);
 			}
 		}
@@ -186,7 +186,7 @@ namespace CoreText {
 		public void GetLineOrigins (NSRange range, CGPoint[] origins)
 		{
 			if (origins is null)
-				throw new ArgumentNullException (nameof (origins));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (origins));
 			if (range.Length != 0 && origins.Length < range.Length)
 				throw new ArgumentException ("origins must contain at least range.Length elements.", nameof (origins));
 			else if (origins.Length < CFArray.GetCount (CTFrameGetLines (Handle)))
@@ -200,7 +200,7 @@ namespace CoreText {
 		public void Draw (CGContext ctx)
 		{
 			if (ctx is null)
-				throw new ArgumentNullException (nameof (ctx));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (ctx));
 
 			CTFrameDraw (Handle, ctx.Handle);
 		}

src/CoreText/CTFramesetter.cs

@@ -69,7 +69,7 @@ namespace CoreText {
 		public CTFrame? GetFrame (NSRange stringRange, CGPath path, CTFrameAttributes? frameAttributes)
 		{
 			if (path is null)
-				throw new ArgumentNullException (nameof (path));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (path));
 			var frame = CTFramesetterCreateFrame (Handle, stringRange, path.Handle, frameAttributes.GetHandle ());
 			if (frame == IntPtr.Zero)
 				return null;
@@ -128,7 +128,7 @@ namespace CoreText {
 		public static CTFramesetter? Create (CTTypesetter typesetter)
 		{
 			if (typesetter is null)
-				throw new ArgumentNullException (nameof (typesetter));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (typesetter));
 
 			var ret = CTFramesetterCreateWithTypesetter (typesetter.Handle);
 			if (ret == IntPtr.Zero)

src/CoreText/CTGlyphInfo.cs

@@ -74,11 +74,11 @@ namespace CoreText {
 		static IntPtr Create (string glyphName, CTFont font, string baseString)
 		{
 			if (glyphName is null)
-				throw new ArgumentNullException (nameof (glyphName));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (glyphName));
 			if (font is null)
-				throw new ArgumentNullException (nameof (font));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			if (baseString is null)
-				throw new ArgumentNullException (nameof (baseString));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (baseString));
 
 			var gnHandle = CFString.CreateNative (glyphName);
 			var bsHandle = CFString.CreateNative (baseString);
@@ -101,9 +101,9 @@ namespace CoreText {
 		static IntPtr Create (CGGlyph glyph, CTFont font, string baseString)
 		{
 			if (font is null)
-				throw new ArgumentNullException (nameof (font));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (font));
 			if (baseString is null)
-				throw new ArgumentNullException (nameof (baseString));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (baseString));
 
 			var bsHandle = CFString.CreateNative (baseString);
 			try {
@@ -124,7 +124,7 @@ namespace CoreText {
 		static IntPtr Create (CGFontIndex cid, CTCharacterCollection collection, string baseString)
 		{
 			if (baseString is null)
-				throw new ArgumentNullException (nameof (baseString));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (baseString));
 
 			var bsHandle = CFString.CreateNative (baseString);
 			try {

src/CoreText/CTLine.cs

@@ -141,7 +141,7 @@ namespace CoreText {
 		public void Draw (CGContext context)
 		{
 			if (context is null)
-				throw new ArgumentNullException (nameof (context));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (context));
 			CTLineDraw (Handle, context.Handle);
 		}
 #endregion
@@ -245,7 +245,7 @@ namespace CoreText {
 		public void EnumerateCaretOffsets (CaretEdgeEnumerator enumerator)
 		{
 			if (enumerator is null)
-				throw new ArgumentNullException (nameof (enumerator));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (enumerator));
 
 			var block_handler = new BlockLiteral ();
 			block_handler.SetupBlockUnsafe (static_enumerate, enumerator);

src/CoreText/CTRunDelegate.cs

@@ -24,6 +24,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 using System.Runtime.Versioning;
@@ -140,7 +143,7 @@ namespace CoreText {
 		static void Deallocate (IntPtr refCon)
 		{
 			var self = GetOperations (refCon);
-			if (self == null)
+			if (self is null)
 				return;
 
 			self.Dispose ();
@@ -150,7 +153,7 @@ namespace CoreText {
 			self.handle = new GCHandle ();
 		}
 
-		internal static CTRunDelegateOperations GetOperations (IntPtr refCon)
+		internal static CTRunDelegateOperations? GetOperations (IntPtr refCon)
 		{
 			GCHandle c = GCHandle.FromIntPtr (refCon);
 
@@ -161,7 +164,7 @@ namespace CoreText {
 		static nfloat GetAscent (IntPtr refCon)
 		{
 			var self = GetOperations (refCon);
-			if (self == null)
+			if (self is null)
 				return 0;
 			return (nfloat) self.GetAscent ();
 		}
@@ -170,7 +173,7 @@ namespace CoreText {
 		static nfloat GetDescent (IntPtr refCon)
 		{
 			var self = GetOperations (refCon);
-			if (self == null)
+			if (self is null)
 				return 0;
 			return (nfloat) self.GetDescent ();
 		}
@@ -179,7 +182,7 @@ namespace CoreText {
 		static nfloat GetWidth (IntPtr refCon)
 		{
 			var self = GetOperations (refCon);
-			if (self == null)
+			if (self is null)
 				return 0;
 			return (nfloat) self.GetWidth ();
 		}
@@ -204,8 +207,8 @@ namespace CoreText {
 
 		static IntPtr Create (CTRunDelegateOperations operations)
 		{
-			if (operations == null)
-				throw new ArgumentNullException (nameof (operations));
+			if (operations is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (operations));
 
 			CTRunDelegateCallbacks callbacks = operations.GetCallbacks ();
 			return CTRunDelegateCreate (ref callbacks, operations.Handle);
@@ -221,7 +224,7 @@ namespace CoreText {
 		[DllImport (Constants.CoreTextLibrary)]
 		static extern IntPtr CTRunDelegateGetRefCon (IntPtr runDelegate);
 
-		public CTRunDelegateOperations Operations {
+		public CTRunDelegateOperations? Operations {
 			get {
 				return CTRunDelegateOperations.GetOperations (CTRunDelegateGetRefCon (Handle));
 			}

src/CoreText/CTStringAttributes.cs

@@ -28,6 +28,8 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
@@ -79,29 +81,29 @@ namespace CoreText {
 
 #if !NET
 	public static partial class CTStringAttributeKey {
-		public static readonly NSString Font;
-		public static readonly NSString ForegroundColorFromContext;
-		public static readonly NSString KerningAdjustment;
-		public static readonly NSString LigatureFormation;
-		public static readonly NSString ForegroundColor;
-		public static readonly NSString BackgroundColor;
-		public static readonly NSString ParagraphStyle;
-		public static readonly NSString StrokeWidth;
-		public static readonly NSString StrokeColor;
-		public static readonly NSString UnderlineStyle;
-		public static readonly NSString Superscript;
-		public static readonly NSString UnderlineColor;
-		public static readonly NSString VerticalForms;
-		public static readonly NSString HorizontalInVerticalForms;
-		public static readonly NSString GlyphInfo;
-		public static readonly NSString CharacterShape;
-		public static readonly NSString RunDelegate;
+		public static readonly NSString? Font;
+		public static readonly NSString? ForegroundColorFromContext;
+		public static readonly NSString? KerningAdjustment;
+		public static readonly NSString? LigatureFormation;
+		public static readonly NSString? ForegroundColor;
+		public static readonly NSString? BackgroundColor;
+		public static readonly NSString? ParagraphStyle;
+		public static readonly NSString? StrokeWidth;
+		public static readonly NSString? StrokeColor;
+		public static readonly NSString? UnderlineStyle;
+		public static readonly NSString? Superscript;
+		public static readonly NSString? UnderlineColor;
+		public static readonly NSString? VerticalForms;
+		public static readonly NSString? HorizontalInVerticalForms;
+		public static readonly NSString? GlyphInfo;
+		public static readonly NSString? CharacterShape;
+		public static readonly NSString? RunDelegate;
 		// Since 6,0
-		internal static readonly NSString BaselineClass;
-		internal static readonly NSString BaselineInfo;
-		internal static readonly NSString BaselineReferenceInfo;
-		internal static readonly NSString BaselineOffset;
-		internal static readonly NSString WritingDirection;
+		internal static readonly NSString? BaselineClass;
+		internal static readonly NSString? BaselineInfo;
+		internal static readonly NSString? BaselineReferenceInfo;
+		internal static readonly NSString? BaselineOffset;
+		internal static readonly NSString? WritingDirection;
 
 		static CTStringAttributeKey ()
 		{
@@ -148,37 +150,37 @@ namespace CoreText {
 
 		public CTStringAttributes (NSDictionary dictionary)
 		{
-			if (dictionary == null)
-				throw new ArgumentNullException ("dictionary");
+			if (dictionary is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 
 		public NSDictionary Dictionary {get; private set;}
 
-		public CTFont Font {
+		public CTFont? Font {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.Font.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.Font.GetHandle ());
 				return h == IntPtr.Zero ? null : new CTFont (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.Font, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.Font!, value);}
 		}
 
 		public bool ForegroundColorFromContext {
 			get {
 				return CFDictionary.GetBooleanValue (Dictionary.Handle, 
-						CTStringAttributeKey.ForegroundColorFromContext.Handle);
+						CTStringAttributeKey.ForegroundColorFromContext.GetHandle ());
 			}
 			set {
 				Adapter.AssertWritable (Dictionary);
 				CFMutableDictionary.SetValue (Dictionary.Handle,
-						CTStringAttributeKey.ForegroundColorFromContext.Handle, value);
+						CTStringAttributeKey.ForegroundColorFromContext.GetHandle (), value);
 			}
 		}
 
 		// Header says 'Value must be a CFNumberRef float' - System/Library/Frameworks/CoreText.framework/Headers/CTStringAttributes.h
 		public float? KerningAdjustment {
 			get {return Adapter.GetSingleValue (Dictionary, CTStringAttributeKey.KerningAdjustment);}
-			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.KerningAdjustment, value);}
+			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.KerningAdjustment!, value);}
 		}
 
 		// Documentation says this must be 'CFNumber', doesn't specify exact type (but implies it's an integer value)
@@ -188,17 +190,17 @@ namespace CoreText {
 				return !value.HasValue ? null : (CTLigatureFormation?) value.Value;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTStringAttributeKey.LigatureFormation,
+				Adapter.SetValue (Dictionary, CTStringAttributeKey.LigatureFormation!,
 						value.HasValue ? (int?) value.Value : null);
 			}
 		}
 
-		public CGColor ForegroundColor {
+		public CGColor? ForegroundColor {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.ForegroundColor.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.ForegroundColor.GetHandle ());
 				return h == IntPtr.Zero ? null : new CGColor (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.ForegroundColor, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.ForegroundColor!, value);}
 		}
 
 #if NET
@@ -210,41 +212,41 @@ namespace CoreText {
 		[iOS (10,0)]
 		[Mac (10,12)]
 #endif
-		public CGColor BackgroundColor {
+		public CGColor? BackgroundColor {
 			get {
 				var h = IntPtr.Zero;
 				var x = CTStringAttributeKey.BackgroundColor;
-				if (x != null)
+				if (x is not null)
 					h = CFDictionary.GetValue (Dictionary.Handle, x.Handle);
 				return h == IntPtr.Zero ? null : new CGColor (h, false);
 			}
 			set {
 				var x = CTStringAttributeKey.BackgroundColor;
-				if (x != null)
+				if (x is not null)
 					Adapter.SetNativeValue (Dictionary, x, value);
 			}
 		}
 
-		public CTParagraphStyle ParagraphStyle {
+		public CTParagraphStyle? ParagraphStyle {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.ParagraphStyle.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.ParagraphStyle.GetHandle ());
 				return h == IntPtr.Zero ? null : new CTParagraphStyle (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.ParagraphStyle, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.ParagraphStyle!, value);}
 		}
 
 		// Documentation says this must be 'CFNumber', doesn't specify exact type (but implies it's a floating point value)
 		public float? StrokeWidth {
 			get {return Adapter.GetSingleValue (Dictionary, CTStringAttributeKey.StrokeWidth);}
-			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.StrokeWidth, value);}
+			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.StrokeWidth!, value);}
 		}
 
-		public CGColor StrokeColor {
+		public CGColor? StrokeColor {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.StrokeColor.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.StrokeColor.GetHandle ());
 				return h == IntPtr.Zero ? null : new CGColor (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.StrokeColor, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.StrokeColor!, value);}
 		}
 
 #if NET
@@ -266,7 +268,7 @@ namespace CoreText {
 		// Documentation says this must be 'CFNumber', doesn't specify exact type
 		public int? UnderlineStyleValue {
 			get {return Adapter.GetInt32Value (Dictionary, CTStringAttributeKey.UnderlineStyle);}
-			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.UnderlineStyle, value);}
+			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.UnderlineStyle!, value);}
 		}
 
 		const int UnderlineStyleMask          = 0x000F;
@@ -304,28 +306,28 @@ namespace CoreText {
 				return !value.HasValue ? null : (CTSuperscriptStyle?) value.Value;
 			}
 			set {
-				Adapter.SetValue (Dictionary, CTStringAttributeKey.Superscript,
+				Adapter.SetValue (Dictionary, CTStringAttributeKey.Superscript!,
 						value.HasValue ? (int?) value.Value : null);
 			}
 		}
 
-		public CGColor UnderlineColor {
+		public CGColor? UnderlineColor {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.UnderlineColor.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.UnderlineColor.GetHandle ());
 				return h == IntPtr.Zero ? null : new CGColor (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.UnderlineColor, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.UnderlineColor!, value);}
 		}
 
 		public bool VerticalForms {
 			get {
 				return CFDictionary.GetBooleanValue (Dictionary.Handle, 
-						CTStringAttributeKey.VerticalForms.Handle);
+						CTStringAttributeKey.VerticalForms.GetHandle ());
 			}
 			set {
 				Adapter.AssertWritable (Dictionary);
 				CFMutableDictionary.SetValue (Dictionary.Handle,
-						CTStringAttributeKey.VerticalForms.Handle, value);
+						CTStringAttributeKey.VerticalForms.GetHandle (), value);
 			}
 		}
 
@@ -343,11 +345,11 @@ namespace CoreText {
 		public int? HorizontalInVerticalForms {
 			get {
 				var x = CTStringAttributeKey.HorizontalInVerticalForms;
-				return x != null ? Adapter.GetInt32Value (Dictionary, x) : null;
+				return x is not null ? Adapter.GetInt32Value (Dictionary, x) : null;
 			}
 			set {
 				var x = CTStringAttributeKey.HorizontalInVerticalForms;
-				if (x != null)
+				if (x is not null)
 					Adapter.SetValue (Dictionary, x, value);
 			}
 		}
@@ -365,38 +367,38 @@ namespace CoreText {
 #endif
 		public float? BaselineOffset {
 			get { return Adapter.GetSingleValue (Dictionary, CTStringAttributeKey.BaselineOffset); }
-			set { Adapter.SetValue (Dictionary, CTStringAttributeKey.BaselineOffset, value); }
+			set { Adapter.SetValue (Dictionary, CTStringAttributeKey.BaselineOffset!, value); }
 		}
 
-		public CTGlyphInfo GlyphInfo {
+		public CTGlyphInfo? GlyphInfo {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.GlyphInfo.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.GlyphInfo.GetHandle ());
 				return h == IntPtr.Zero ? null : new CTGlyphInfo (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.GlyphInfo, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.GlyphInfo!, value);}
 		}
 
 		public int? CharacterShape {
 			get {return Adapter.GetInt32Value (Dictionary, CTStringAttributeKey.CharacterShape);}
-			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.CharacterShape, value);}
+			set {Adapter.SetValue (Dictionary, CTStringAttributeKey.CharacterShape!, value);}
 		}
 
-		public CTRunDelegate RunDelegate {
+		public CTRunDelegate? RunDelegate {
 			get {
-				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.RunDelegate.Handle);
+				var h = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.RunDelegate.GetHandle ());
 				return h == IntPtr.Zero ? null : new CTRunDelegate (h, false);
 			}
-			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.RunDelegate, value);}
+			set {Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.RunDelegate!, value);}
 		}
 
 		public CTBaselineClass? BaselineClass {
 			get {
-				var value = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.BaselineClass.Handle);
+				var value = CFDictionary.GetValue (Dictionary.Handle, CTStringAttributeKey.BaselineClass.GetHandle ());
 				return value == IntPtr.Zero ? (CTBaselineClass?) null : CTBaselineClassID.FromHandle (value);
 			}
 			set {
-				var ns_value = value == null ? null : CTBaselineClassID.ToNSString (value.Value);
-				Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.BaselineClass, ns_value);
+				var ns_value = value is null ? null : CTBaselineClassID.ToNSString (value.Value);
+				Adapter.SetNativeValue (Dictionary, CTStringAttributeKey.BaselineClass!, ns_value);
 			}
 		}
 
@@ -410,16 +412,16 @@ namespace CoreText {
 			SetBaseline (baselineClass, offset, CTStringAttributeKey.BaselineReferenceInfo);
 		}
 
-		void SetBaseline (CTBaselineClass baselineClass, double offset, NSString infoKey)
+		void SetBaseline (CTBaselineClass baselineClass, double offset, NSString? infoKey)
 		{
-			var ptr = CFDictionary.GetValue (Dictionary.Handle, infoKey.Handle);
+			var ptr = CFDictionary.GetValue (Dictionary.Handle, infoKey.GetHandle ());
 			var dict = ptr == IntPtr.Zero ? new NSMutableDictionary () : new NSMutableDictionary (ptr);
 
 			var key = CTBaselineClassID.ToNSString (baselineClass);
-			Adapter.SetValue (dict, key, new NSNumber (offset));
+			Adapter.SetValue (dict, key!, new NSNumber (offset));
 
 			if (ptr == IntPtr.Zero)
-				Adapter.SetNativeValue (Dictionary, infoKey, (INativeObject)dict);
+				Adapter.SetNativeValue (Dictionary, infoKey!, (INativeObject)dict);
 		}
 
 		// 'Value must be a CFArray of CFNumberRefs' - System/Library/Frameworks/CoreText.framework/Headers/CTStringAttributes.h
@@ -433,7 +435,7 @@ namespace CoreText {
 			}
 
 			var array = CFArray.Create (ptrs);
-			CFMutableDictionary.SetValue (Dictionary.Handle, CTStringAttributeKey.WritingDirection.Handle, array);
+			CFMutableDictionary.SetValue (Dictionary.Handle, CTStringAttributeKey.WritingDirection.GetHandle (), array);
 			GC.KeepAlive (numbers); // make sure the numbers aren't freed until we're done with them
 		}
 	}

src/CoreText/CTTextTab.cs

@@ -70,7 +70,7 @@ namespace CoreText {
 		public CTTextTabOptions (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 

src/CoreText/CTTypesetter.cs

@@ -61,7 +61,7 @@ namespace CoreText {
 		public CTTypesetterOptions (NSDictionary dictionary)
 		{
 			if (dictionary is null)
-				throw new ArgumentNullException (nameof (dictionary));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (dictionary));
 			Dictionary = dictionary;
 		}
 

src/CoreText/CTTypesetterOptionKeyCompat.cs

@@ -7,6 +7,8 @@
 // Copyright 2018 Microsoft Corporation.
 //
 
+#nullable enable
+
 #if !NET
 using System;
 using ObjCRuntime;

src/CoreText/ConstructorError.cs

@@ -24,6 +24,8 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 
@@ -36,12 +38,6 @@ namespace CoreText {
 
 	static class ConstructorError {
 
-		public static Exception ArgumentNull (object self, string argument)
-		{
-			GC.SuppressFinalize (self);
-			return new ArgumentNullException (argument);
-		}
-
 		public static Exception Unknown (object self)
 		{
 			GC.SuppressFinalize (self);

src/OpenGL/CGLEnums.cs

@@ -20,6 +20,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using ObjCRuntime;
 

src/OpenGL/CGLPixelFormat.cs

@@ -89,7 +89,7 @@ namespace OpenGL {
 		static IntPtr Create (CGLPixelFormatAttribute[] attributes, out int npix)
 		{
 			if (attributes is null)
-				throw new ArgumentNullException (nameof (attributes));
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (attributes));
 			IntPtr pixelFormatOut;
 			var marshalAttribs = new CGLPixelFormatAttribute [attributes.Length + 1];
 

src/OpenGL/FrameEventArgs.cs

@@ -25,6 +25,8 @@
 //
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 using System;
 

src/OpenGL/IGameWindow.cs

@@ -25,6 +25,9 @@
 //
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/INativeWindow.cs

@@ -25,6 +25,8 @@
 //
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/MonoMacGameView.cs

@@ -22,7 +22,9 @@
 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-// 
+//
+
+#nullable enable
 
 #if OPENTK_DLL
 
@@ -41,11 +43,11 @@ namespace OpenTK.Platform.MacOS
 	public class MonoMacGameView : AppKit.NSView, IGameWindow
 	{
 		bool disposed;
-		NSOpenGLContext openGLContext;
-		NSOpenGLPixelFormat pixelFormat;
-		CVDisplayLink displayLink;
-		NSObject notificationProxy;
-		NSTimer animationTimer;
+		NSOpenGLContext? openGLContext;
+		NSOpenGLPixelFormat? pixelFormat;
+		CVDisplayLink? displayLink;
+		NSObject? notificationProxy;
+		NSTimer? animationTimer;
 		bool animating;
 		bool displayLinkSupported = false;
 		WindowState windowState = WindowState.Normal;
@@ -64,7 +66,7 @@ namespace OpenTK.Platform.MacOS
 		{
 		}
 
-		public MonoMacGameView (CGRect frame, NSOpenGLContext context) : base(frame)
+		public MonoMacGameView (CGRect frame, NSOpenGLContext? context) : base(frame)
 		{
 			var attribs = new object [] {
 				NSOpenGLPixelFormatAttribute.NoRecovery,
@@ -85,11 +87,11 @@ namespace OpenTK.Platform.MacOS
 				pixelFormat = new NSOpenGLPixelFormat (attribs);
 			}
 
-			if (pixelFormat == null)
+			if (pixelFormat is null)
 				Console.WriteLine ("No OpenGL pixel format");
 
 			// NSOpenGLView does not handle context sharing, so we draw to a custom NSView instead
-			openGLContext = new NSOpenGLContext (pixelFormat, context);
+			openGLContext = new NSOpenGLContext (ActualPixelFormat, context);
 
 			openGLContext.MakeCurrentContext ();
 
@@ -108,7 +110,7 @@ namespace OpenTK.Platform.MacOS
 			if (animating) {
 				if (displayLinkSupported) {
 					// Render Scene only if the display link is running
-					if (displayLink.IsRunning)
+					if (displayLink?.IsRunning == true)
 						RenderScene ();
 				} else {
 					RenderScene ();
@@ -120,24 +122,40 @@ namespace OpenTK.Platform.MacOS
 		public override void LockFocus ()
 		{
 			base.LockFocus ();
-			if (openGLContext.View != this)
-				openGLContext.View = this;
+			if (ActualOpenGLContext.View != this)
+				ActualOpenGLContext.View = this;
 		}
 
-		public NSOpenGLContext OpenGLContext {
-			get { return openGLContext; }
+		public NSOpenGLContext? OpenGLContext {
+			get => openGLContext;
 		}
 
-		public NSOpenGLPixelFormat PixelFormat {
-			get { return pixelFormat; }
+		NSOpenGLContext ActualOpenGLContext {
+			get {
+				if (openGLContext is null)
+					throw new InvalidOperationException ("Operation requires an OpenGLContext, which hasn't been created yet.");
+				return openGLContext;
+			}
 		}
 
-		NSViewController GetViewController ()
+		public NSOpenGLPixelFormat? PixelFormat {
+			get => pixelFormat;
+		}
+
+		NSOpenGLPixelFormat ActualPixelFormat {
+			get {
+				if (pixelFormat is null)
+					throw new InvalidOperationException ("Operation requires a PixelFormat that cannot be null.");
+				return pixelFormat;
+			}
+		}
+
+		NSViewController? GetViewController ()
 		{
-			NSResponder r = this;
-			while (r != null) {
+			NSResponder? r = this;
+			while (r is not null) {
 				var c = r as NSViewController;
-				if (c != null)
+				if (c is not null)
 					return c;
 				r = r.NextResponder;
 			}
@@ -158,7 +176,7 @@ namespace OpenTK.Platform.MacOS
 		{
 			if (!animating) {
 				if (displayLinkSupported) {
-					if (displayLink != null && !displayLink.IsRunning)
+					if (displayLink is not null && !displayLink.IsRunning)
 						displayLink.Start ();
 				} else {
 					// Can't use TimeSpan.FromSeconds() as that only has 1ms
@@ -191,10 +209,10 @@ namespace OpenTK.Platform.MacOS
 		{
 			if (animating) {
 				if (displayLinkSupported) {
-					if (displayLink != null && displayLink.IsRunning)
+					if (displayLink is not null && displayLink.IsRunning)
 						displayLink.Stop ();
 
-				} else {
+				} else if (animationTimer is not null) {
 					animationTimer.Invalidate ();
 					animationTimer = null;
 				}
@@ -207,7 +225,8 @@ namespace OpenTK.Platform.MacOS
 		{
 			Stop ();
 			displayLink = null;
-			NSNotificationCenter.DefaultCenter.RemoveObserver (notificationProxy); 
+			if (notificationProxy is not null)
+				NSNotificationCenter.DefaultCenter.RemoveObserver (notificationProxy);
 		}
 
 		void AssertValid ()
@@ -216,23 +235,17 @@ namespace OpenTK.Platform.MacOS
 				throw new ObjectDisposedException ("");
 		}
 
-		void AssertContext ()
-		{
-			if (OpenGLContext == null)
-				throw new InvalidOperationException ("Operation requires an OpenGLContext, which hasn't been created yet.");
-		}
-
 		public virtual string Title {
 			get {
 				AssertValid ();
-				if (Window != null)
+				if (Window is not null)
 					return Window.Title;
 				else
 					throw new NotSupportedException();
 			}
 			set {
 				AssertValid ();
-				if (Window != null)
+				if (Window is not null)
 					Window.Title = value;
 				else
 					throw new NotSupportedException();
@@ -242,7 +255,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnTitleChanged (EventArgs e)
 		{
 			var h = TitleChanged;
-			if (h != null)
+			if (h is not null)
 				h (this, EventArgs.Empty);
 		}
 
@@ -267,7 +280,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnVisibleChanged (EventArgs e)
 		{
 			var h = VisibleChanged;
-			if (h != null)
+			if (h is not null)
 				h (this, EventArgs.Empty);
 		}
 
@@ -292,7 +305,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnWindowStateChanged (EventArgs e)
 		{
 			var h = WindowStateChanged;
-			if (h != null)
+			if (h is not null)
 				h (this, EventArgs.Empty);
 		}
 
@@ -327,13 +340,13 @@ namespace OpenTK.Platform.MacOS
 					size = value;
 					// This method will be called on the main thread when resizing, but we may be drawing on a secondary thread through the display link
 					// Add a mutex around to avoid the threads accessing the context simultaneously
-					openGLContext.CGLContext.Lock ();
+					ActualOpenGLContext.CGLContext.Lock ();
 
 					// Delegate to the scene object to update for a change in the view size
 					OnResize (EventArgs.Empty);
-					openGLContext.Update ();
+					ActualOpenGLContext.Update ();
 
-					openGLContext.CGLContext.Unlock ();					
+					ActualOpenGLContext.CGLContext.Unlock ();
 				}
 			}
 		}
@@ -341,7 +354,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnResize (EventArgs e)
 		{
 			var h = Resize;
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
@@ -384,7 +397,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnClosed (EventArgs e)
 		{
 			var h = Closed;
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
@@ -405,7 +418,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnDisposed (EventArgs e)
 		{
 			var h = Disposed;
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
@@ -427,16 +440,14 @@ namespace OpenTK.Platform.MacOS
 		public virtual void MakeCurrent ()
 		{
 			AssertValid ();
-			AssertContext ();
-			OpenGLContext.MakeCurrentContext ();
+			ActualOpenGLContext.MakeCurrentContext ();
 		}
 
 		public virtual void SwapBuffers ()
 		{
 			AssertValid ();
-			AssertContext ();
 			// basically SwapBuffers is the same as FlushBuffer on OSX
-			OpenGLContext.FlushBuffer ();
+			ActualOpenGLContext.FlushBuffer ();
 		}
 
 		private bool SwapInterval { get; set; }
@@ -454,7 +465,7 @@ namespace OpenTK.Platform.MacOS
 			OnLoad (EventArgs.Empty);
 
 			// Synchronize buffer swaps with vertical refresh rate
-			openGLContext.SwapInterval = SwapInterval;
+			ActualOpenGLContext.SwapInterval = SwapInterval;
 
 			if (displayLinkSupported) 
 				SetupDisplayLink ();
@@ -478,7 +489,7 @@ namespace OpenTK.Platform.MacOS
 			DisplaylinkSupported = false;
 
 			// Synchronize buffer swaps with vertical refresh rate
-			openGLContext.SwapInterval = SwapInterval;
+			ActualOpenGLContext.SwapInterval = SwapInterval;
 
 			if (displayLinkSupported)
 				SetupDisplayLink ();
@@ -492,10 +503,10 @@ namespace OpenTK.Platform.MacOS
 			// This method will be called on both the main thread (through DrawRect:) and a secondary thread (through the display link rendering loop)
 			// Also, when resizing the view, Reshape is called on the main thread, but we may be drawing on a secondary thread
 			// Add a mutex around to avoid the threads accessing the context simultaneously 
-			openGLContext.CGLContext.Lock ();
+			ActualOpenGLContext.CGLContext.Lock ();
 
 			// Make sure we draw to the right context
-			openGLContext.MakeCurrentContext ();
+			ActualOpenGLContext.MakeCurrentContext ();
 
 			var curUpdateTime = DateTime.Now;
 			if (prevUpdateTime.Ticks == 0) {
@@ -523,14 +534,14 @@ namespace OpenTK.Platform.MacOS
 			OnRenderFrame (renderEventArgs);
 			prevRenderTime = curRenderTime;
 
-			openGLContext.FlushBuffer ();
+			ActualOpenGLContext.FlushBuffer ();
 
-			openGLContext.CGLContext.Unlock ();
+			ActualOpenGLContext.CGLContext.Unlock ();
 		}
 
 		private void SetupDisplayLink ()
 		{
-			if (displayLink != null)
+			if (displayLink is not null)
 				return;
 
 			// Create a display link capable of being used with all active displays
@@ -540,8 +551,8 @@ namespace OpenTK.Platform.MacOS
 			displayLink.SetOutputCallback (MyDisplayLinkOutputCallback);
 
 			// Set the display link for the current renderer
-			CGLContext cglContext = openGLContext.CGLContext;
-			CGLPixelFormat cglPixelFormat = PixelFormat.CGLPixelFormat;
+			CGLContext cglContext = ActualOpenGLContext.CGLContext;
+			CGLPixelFormat cglPixelFormat = ActualPixelFormat.CGLPixelFormat;
 			displayLink.SetCurrentDisplay (cglContext, cglPixelFormat);
 
 		}
@@ -566,7 +577,7 @@ namespace OpenTK.Platform.MacOS
 		protected virtual void OnLoad (EventArgs e)
 		{
 			var h = Load;
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
@@ -574,21 +585,21 @@ namespace OpenTK.Platform.MacOS
 		{
 			var h = Unload;
 			Stop ();
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
 		protected virtual void OnUpdateFrame (FrameEventArgs e)
 		{
 			var h = UpdateFrame;
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
 		protected virtual void OnRenderFrame (FrameEventArgs e)
 		{
 			var h = RenderFrame;
-			if (h != null)
+			if (h is not null)
 				h (this, e);
 		}
 
@@ -597,17 +608,17 @@ namespace OpenTK.Platform.MacOS
 			remove { throw new NotSupportedException ();}
 		}
 
-		public event EventHandler<EventArgs> Resize;
+		public event EventHandler<EventArgs>? Resize;
 
 		event EventHandler<CancelEventArgs> INativeWindow.Closing {
 			add { throw new NotSupportedException ();}
 			remove { throw new NotSupportedException ();}
 		}
 
-		public event EventHandler<EventArgs> Closed;
-		public event EventHandler<EventArgs> Disposed;
-		public event EventHandler<EventArgs> TitleChanged;
-		public event EventHandler<EventArgs> VisibleChanged;
+		public event EventHandler<EventArgs>? Closed;
+		public event EventHandler<EventArgs>? Disposed;
+		public event EventHandler<EventArgs>? TitleChanged;
+		public event EventHandler<EventArgs>? VisibleChanged;
 
 		event EventHandler<EventArgs> INativeWindow.FocusedChanged {
 			add { throw new NotSupportedException ();}
@@ -619,7 +630,7 @@ namespace OpenTK.Platform.MacOS
 			remove { throw new NotSupportedException ();}
 		}
 
-		public event EventHandler<EventArgs> WindowStateChanged;
+		public event EventHandler<EventArgs>? WindowStateChanged;
 
 		//		event EventHandler<KeyPressEventArgs> INativeWindow.KeyPress {
 		//			add { throw new NotSupportedException ();}
@@ -630,10 +641,10 @@ namespace OpenTK.Platform.MacOS
 			remove { throw new NotSupportedException ();}
 		}
 
-		public event EventHandler<EventArgs> Load;
-		public event EventHandler<EventArgs> Unload;
-		public event EventHandler<FrameEventArgs> UpdateFrame;
-		public event EventHandler<FrameEventArgs> RenderFrame;
+		public event EventHandler<EventArgs>? Load;
+		public event EventHandler<EventArgs>? Unload;
+		public event EventHandler<FrameEventArgs>? UpdateFrame;
+		public event EventHandler<FrameEventArgs>? RenderFrame;
 	}
 }
 

src/OpenGL/OpenTK/Audio/BlittableValueType.cs

@@ -25,6 +25,8 @@
 //
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;
@@ -140,8 +142,8 @@ namespace OpenTK.Audio
             StructLayoutAttribute[] attr = (StructLayoutAttribute[])
                 type.GetCustomAttributes(typeof(StructLayoutAttribute), true);
 
-            if ((attr == null) ||
-                (attr != null && attr.Length > 0 && attr[0].Value != LayoutKind.Explicit && attr[0].Pack != 1))
+            if ((attr is null) ||
+                (attr is not null && attr.Length > 0 && attr[0].Value != LayoutKind.Explicit && attr[0].Pack != 1))
                 return false;
 
             return true;

src/OpenGL/OpenTK/Audio/ContextHandle.cs

@@ -6,6 +6,8 @@
  */
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/OpenTK/Audio/OpenAL/AL/AL.cs

@@ -7,6 +7,9 @@
  * http://www.OpenTK.net */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 #if OPENTK_DLL
 
 using System;
@@ -499,7 +502,8 @@ namespace OpenTK.Audio.OpenAL
         [CLSCompliant(false)]
         public static void DeleteSources(uint[] sources)
         {
-            if (sources == null) throw new ArgumentNullException();
+            if (sources is null)
+                ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (sources));
             if (sources.Length == 0) throw new ArgumentOutOfRangeException();
             DeleteBuffers(sources.Length, ref sources[0]);
         }
@@ -508,7 +512,8 @@ namespace OpenTK.Audio.OpenAL
         /// <param name="sources">An array of source names identifying the sources to be deleted.</param>
         public static void DeleteSources(int[] sources)
         {
-            if (sources == null) throw new ArgumentNullException();
+            if (sources is null)
+                ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (sources));
             if (sources.Length == 0) throw new ArgumentOutOfRangeException();
             DeleteBuffers(sources.Length, ref sources[0]);
         }
@@ -1389,7 +1394,8 @@ namespace OpenTK.Audio.OpenAL
         [CLSCompliant(false)]
         public static void DeleteBuffers(uint[] buffers)
         {
-            if (buffers == null) throw new ArgumentNullException();
+            if (buffers is null)
+                ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (buffers));
             if (buffers.Length == 0) throw new ArgumentOutOfRangeException();
             DeleteBuffers(buffers.Length, ref buffers[0]);
         }
@@ -1398,7 +1404,8 @@ namespace OpenTK.Audio.OpenAL
         /// <param name="buffers">Pointer to an array of buffer names identifying the buffers to be deleted.</param>
         public static void DeleteBuffers(int[] buffers)
         {
-            if (buffers == null) throw new ArgumentNullException();
+            if (buffers is null)
+                ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (buffers));
             if (buffers.Length == 0) throw new ArgumentOutOfRangeException();
             DeleteBuffers(buffers.Length, ref buffers[0]);
         }

src/OpenGL/OpenTK/Audio/OpenAL/AL/ALEnums.cs

@@ -7,6 +7,8 @@
  * http://www.OpenTK.net */
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/OpenTK/Audio/OpenAL/Alc/Alc.cs

@@ -7,6 +7,8 @@
  * http://www.OpenTK.net */
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/OpenTK/Audio/OpenAL/Alc/AlcEnums.cs

@@ -7,6 +7,8 @@
  * http://www.OpenTK.net */
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/OpenTK/Graphics/Color4.cs

@@ -25,6 +25,8 @@
 //
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/OpenTK/Graphics/OpenGL/GL.cs

@@ -23,6 +23,8 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 #if OPENTK_DLL
 
 namespace OpenTK.Graphics.OpenGL

src/OpenGL/OpenTK/Graphics/OpenGL/GLCore.cs

@@ -23,6 +23,8 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 #if OPENTK_DLL
 
 namespace OpenTK.Graphics.OpenGL

src/OpenGL/OpenTK/Graphics/OpenGL/GLEnums.cs

@@ -23,6 +23,8 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/OpenTK/Graphics/OpenGL/GLHelper.cs

@@ -25,6 +25,9 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 #if OPENTK_DLL
 
 #region --- Using Directives ---

src/OpenGL/OpenTK/Math/Half.cs

@@ -56,6 +56,8 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 #endregion --- License ---
 
+#nullable enable
+
 using System;
 using System.IO;
 using System.Runtime.InteropServices;

src/OpenGL/OpenTK/Math/MathHelper.cs

@@ -8,6 +8,8 @@
  */
 #endregion
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Text;

src/OpenGL/OpenTK/Math/Matrix2.cs

@@ -23,6 +23,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 
@@ -203,7 +206,8 @@ namespace OpenTK
         /// <param name="floatArray">The array of floats for the components of the matrix.</param>
         public Matrix2(float[] floatArray)
         {
-            if (floatArray == null || floatArray.GetLength(0) < 9) throw new MissingFieldException();
+            if (floatArray is null || floatArray.GetLength (0) < 9)
+                throw new MissingFieldException ();
 
             this.R0C0 = floatArray[0];
             this.R0C1 = floatArray[1];

src/OpenGL/OpenTK/Math/Matrix3.cs

@@ -22,6 +22,8 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 
@@ -274,7 +276,8 @@ namespace OpenTK
         /// <param name="floatArray">The array of floats for the components of the matrix.</param>
         public Matrix3(float[] floatArray)
         {
-            if (floatArray == null || floatArray.GetLength(0) < 9) throw new MissingFieldException();
+            if (floatArray is null || floatArray.GetLength (0) < 9)
+                throw new MissingFieldException ();
 
             this.R0C0 = floatArray[0];
             this.R0C1 = floatArray[1];

src/OpenGL/OpenTK/Math/Matrix3d.cs

@@ -22,6 +22,8 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 
@@ -275,7 +277,8 @@ namespace OpenTK
         /// <param name="doubleArray">The array of doubles for the components of the matrix.</param>
         public Matrix3d(double[] doubleArray)
         {
-            if (doubleArray == null || doubleArray.GetLength(0) < 9) throw new MissingFieldException();
+            if (doubleArray is null || doubleArray.GetLength (0) < 9)
+                throw new MissingFieldException ();
 
             this.R0C0 = doubleArray[0];
             this.R0C1 = doubleArray[1];

src/OpenGL/OpenTK/Math/Matrix4.cs

@@ -22,6 +22,8 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 

src/OpenGL/OpenTK/Math/Matrix4d.cs

@@ -22,6 +22,8 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+
 using System;
 using System.Runtime.InteropServices;
 

src/OpenGL/OpenTK/Math/Quaternion.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;

src/OpenGL/OpenTK/Math/Quaterniond.cs

@@ -22,6 +22,9 @@ SOFTWARE.
 */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;
@@ -746,7 +749,8 @@ namespace OpenTK
         /// <param name="doubleArray">The array of doubles for the components of the Quaterniond.</param>
         public Quaterniond(double[] doubleArray)
         {
-            if (doubleArray == null || doubleArray.GetLength(0) < 4) throw new MissingFieldException();
+            if (doubleArray is null || doubleArray.GetLength (0) < 4)
+                throw new MissingFieldException ();
 
             this.W = doubleArray[0];
             this.X = doubleArray[1];

src/OpenGL/OpenTK/Math/Vector2.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 #if !NET

src/OpenGL/OpenTK/Math/Vector2d.cs

@@ -22,6 +22,9 @@ SOFTWARE.
 */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 

src/OpenGL/OpenTK/Math/Vector2h.cs

@@ -27,6 +27,9 @@ using System.IO;
 using System.Runtime.InteropServices;
 using System.Runtime.Serialization;
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 #if !NET
 namespace OpenTK
 {

src/OpenGL/OpenTK/Math/Vector3.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 using System.Xml.Serialization;

src/OpenGL/OpenTK/Math/Vector3d.cs

@@ -22,6 +22,9 @@ SOFTWARE.
 */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 using System.Xml.Serialization;

src/OpenGL/OpenTK/Math/Vector3h.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.IO;
 using System.Runtime.InteropServices;

src/OpenGL/OpenTK/Math/Vector4.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 using System.Xml.Serialization;

src/OpenGL/OpenTK/Math/Vector4d.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.Runtime.InteropServices;
 using System.Xml.Serialization;

src/OpenGL/OpenTK/Math/Vector4h.cs

@@ -22,6 +22,9 @@ SOFTWARE.
  */
 #endregion
 
+#nullable enable
+#pragma warning disable CS3021 // Type or member does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
+
 using System;
 using System.IO;
 using System.Runtime.InteropServices;

src/OpenGL/WindowBorder.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/OpenGL/WindowState.cs

@@ -6,6 +6,8 @@
 */
 #endregion
 
+#nullable enable
+
 #if OPENTK_DLL
 
 using System;

src/PassKit/PKPaymentRequest.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 using Foundation;
 using ObjCRuntime;
@@ -9,13 +11,13 @@ namespace PassKit {
 		static public PKContactFields GetValue (NSSet set)
 		{
 			var fields = PKContactFields.None;
-			if (set == null)
+			if (set is null)
 				return fields;
 
 			foreach (PKContactFields value in Enum.GetValues (typeof (PKContactFields))) {
 				var constant = value.GetConstant ();
 				// None does not have an associated native value and Contains would throw an ANE
-				if ((constant != null) && set.Contains (constant))
+				if ((constant is not null) && set.Contains (constant))
 				    fields |= value;
 			}
 			return fields;
@@ -31,7 +33,7 @@ namespace PassKit {
 				if (values.HasFlag (value)) {
 					var constant = value.GetConstant ();
 					// None does not have an associated native value and Contains would throw an ANE
-					if (constant != null)
+					if (constant is not null)
 						set.Add (constant);
 				}
 			}

src/SceneKit/SCNMatrix4_dotnet.cs

@@ -1,7 +1,4 @@
 /*
- * This keeps the code of OpenTK's Matrix4 almost intact, except we replace the
- * Vector4 with a SCNVector4
- 
 Copyright (c) 2006 - 2008 The Open Toolkit library.
 Copyright (c) 2014 Xamarin Inc.  All rights reserved
 
@@ -52,28 +49,55 @@ using pfloat = System.Runtime.InteropServices.NFloat;
 
 namespace SceneKit {
 	/// <summary>
-	/// Represents a 4x4 Matrix
+	/// Represents a 4x4 matrix using a column-major memory layout.
 	/// </summary>
 	[Serializable]
 	public struct SCNMatrix4 : IEquatable<SCNMatrix4> {
 		#region Fields
 
+		/*
+		 * SCNMatrix4 is defined like this for iOS, tvOS and watchOS:
+		 *
+		 * 	typedef struct SCNMatrix4 {
+		 * 	    float m11, m12, m13, m14;
+		 * 	    float m21, m22, m23, m24;
+		 * 	    float m31, m32, m33, m34;
+		 * 	    float m41, m42, m43, m44;
+		 * 	} SCNMatrix4;
+		 *
+		 * and like this for macOS:
+		 *
+		 * 	struct CATransform3D
+		 * 	{
+		 * 	  CGFloat m11, m12, m13, m14;
+		 * 	  CGFloat m21, m22, m23, m24;
+		 * 	  CGFloat m31, m32, m33, m34;
+		 * 	  CGFloat m41, m42, m43, m44;
+		 * 	};
+		 * 	typedef CATransform3D SCNMatrix4;
+		 *
+		 * It's not obvious from this definitions whether the matrix is row-major or column-major, and neither the documentation
+		 * nor the headers are particularly helpful, but it's possible to do some math to figure it out. See this for more info:
+		 * https://github.com/xamarin/xamarin-macios/issues/15094#issuecomment-1139699662 (result: SCNMatrix4 is using a column-major layout)
+		 *
+		 **/
+
 		/// <summary>
 		/// Left-most column of the matrix
 		/// </summary>
-		public SCNVector4 Column0;
+		public SCNVector4 Column0; // m11, m12, m13, m14
 		/// <summary>
 		/// 2nd column of the matrix
 		/// </summary>
-		public SCNVector4 Column1;
+		public SCNVector4 Column1; // m21, m22, m23, m24
 		/// <summary>
 		/// 3rd column of the matrix
 		/// </summary>
-		public SCNVector4 Column2;
+		public SCNVector4 Column2; // m31, m32, m33, m34
 		/// <summary>
 		/// Right-most column of the matrix
 		/// </summary>
-		public SCNVector4 Column3;
+		public SCNVector4 Column3; // m41, m42, m43, m44
 
 		/// <summary>
 		/// The identity matrix
@@ -133,10 +157,10 @@ namespace SceneKit {
 #if !WATCH
 		public SCNMatrix4 (CoreAnimation.CATransform3D transform)
 		{
-			Column0 = new SCNVector4 ((pfloat) transform.M11, (pfloat) transform.M21, (pfloat) transform.M31, (pfloat) transform.M41);
-			Column1 = new SCNVector4 ((pfloat) transform.M12, (pfloat) transform.M22, (pfloat) transform.M32, (pfloat) transform.M42);
-			Column2 = new SCNVector4 ((pfloat) transform.M13, (pfloat) transform.M23, (pfloat) transform.M33, (pfloat) transform.M43);
-			Column3 = new SCNVector4 ((pfloat) transform.M14, (pfloat) transform.M24, (pfloat) transform.M34, (pfloat) transform.M44);
+			Column0 = new SCNVector4 ((pfloat) transform.M11, (pfloat) transform.M12, (pfloat) transform.M13, (pfloat) transform.M14);
+			Column1 = new SCNVector4 ((pfloat) transform.M21, (pfloat) transform.M22, (pfloat) transform.M23, (pfloat) transform.M24);
+			Column2 = new SCNVector4 ((pfloat) transform.M31, (pfloat) transform.M32, (pfloat) transform.M33, (pfloat) transform.M34);
+			Column3 = new SCNVector4 ((pfloat) transform.M41, (pfloat) transform.M42, (pfloat) transform.M43, (pfloat) transform.M44);
 		}
 #endif
 
@@ -167,10 +191,10 @@ namespace SceneKit {
 		public SCNVector4 Row0 {
 			get { return new SCNVector4 (Column0.X, Column1.X, Column2.X, Column3.X); }
 			set {
-				M11 = value.X;
-				M12 = value.Y;
-				M13 = value.Z;
-				M14 = value.W;
+				Column0.X = value.X;
+				Column1.X = value.Y;
+				Column2.X = value.Z;
+				Column3.X = value.W;
 			}
 		}
 
@@ -180,10 +204,10 @@ namespace SceneKit {
 		public SCNVector4 Row1 {
 			get { return new SCNVector4 (Column0.Y, Column1.Y, Column2.Y, Column3.Y); }
 			set {
-				M21 = value.X;
-				M22 = value.Y;
-				M23 = value.Z;
-				M24 = value.W;
+				Column0.Y = value.X;
+				Column1.Y = value.Y;
+				Column2.Y = value.Z;
+				Column3.Y = value.W;
 			}
 		}
 
@@ -193,10 +217,10 @@ namespace SceneKit {
 		public SCNVector4 Row2 {
 			get { return new SCNVector4 (Column0.Z, Column1.Z, Column2.Z, Column3.Z); }
 			set {
-				M31 = value.X;
-				M32 = value.Y;
-				M33 = value.Z;
-				M34 = value.W;
+				Column0.Z = value.X;
+				Column1.Z = value.Y;
+				Column2.Z = value.Z;
+				Column3.Z = value.W;
 			}
 		}
 
@@ -206,90 +230,90 @@ namespace SceneKit {
 		public SCNVector4 Row3 {
 			get { return new SCNVector4 (Column0.W, Column1.W, Column2.W, Column3.W); }
 			set {
-				M41 = value.X;
-				M42 = value.Y;
-				M43 = value.Z;
-				M44 = value.W;
+				Column0.W = value.X;
+				Column1.W = value.Y;
+				Column2.W = value.Z;
+				Column3.W = value.W;
 			}
 		}
 
 		/// <summary>
-		/// Gets or sets the value at row 1, column 1 of this instance.
+		/// Gets or sets the value at column 1, row 1 of this instance.
 		/// </summary>
 		public pfloat M11 { get { return Column0.X; } set { Column0.X = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 1, column 2 of this instance.
+		/// Gets or sets the value at column 1, row 2 of this instance.
 		/// </summary>
-		public pfloat M12 { get { return Column1.X; } set { Column1.X = value; } }
+		public pfloat M12 { get { return Column0.Y; } set { Column0.Y = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 1, column 3 of this instance.
+		/// Gets or sets the value at column 1, row 3 of this instance.
 		/// </summary>
-		public pfloat M13 { get { return Column2.X; } set { Column2.X = value; } }
+		public pfloat M13 { get { return Column0.Z; } set { Column0.Z = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 1, column 4 of this instance.
+		/// Gets or sets the value at column 1, row 4 of this instance.
 		/// </summary>
-		public pfloat M14 { get { return Column3.X; } set { Column3.X = value; } }
+		public pfloat M14 { get { return Column0.W; } set { Column0.W = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 2, column 1 of this instance.
+		/// Gets or sets the value at column 2, row 1 of this instance.
 		/// </summary>
-		public pfloat M21 { get { return Column0.Y; } set { Column0.Y = value; } }
+		public pfloat M21 { get { return Column1.X; } set { Column1.X = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 2, column 2 of this instance.
+		/// Gets or sets the value at column 2, row 2 of this instance.
 		/// </summary>
 		public pfloat M22 { get { return Column1.Y; } set { Column1.Y = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 2, column 3 of this instance.
+		/// Gets or sets the value at column 2, row 3 of this instance.
 		/// </summary>
-		public pfloat M23 { get { return Column2.Y; } set { Column2.Y = value; } }
+		public pfloat M23 { get { return Column1.Z; } set { Column1.Z = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 2, column 4 of this instance.
+		/// Gets or sets the value at column 2, row 4 of this instance.
 		/// </summary>
-		public pfloat M24 { get { return Column3.Y; } set { Column3.Y = value; } }
+		public pfloat M24 { get { return Column1.W; } set { Column1.W = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 3, column 1 of this instance.
+		/// Gets or sets the value at column 3, row 1 of this instance.
 		/// </summary>
-		public pfloat M31 { get { return Column0.Z; } set { Column0.Z = value; } }
+		public pfloat M31 { get { return Column2.X; } set { Column2.X = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 3, column 2 of this instance.
+		/// Gets or sets the value at column 3, row 2 of this instance.
 		/// </summary>
-		public pfloat M32 { get { return Column1.Z; } set { Column1.Z = value; } }
+		public pfloat M32 { get { return Column2.Y; } set { Column2.Y = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 3, column 3 of this instance.
+		/// Gets or sets the value at column 3, row 3 of this instance.
 		/// </summary>
 		public pfloat M33 { get { return Column2.Z; } set { Column2.Z = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 3, column 4 of this instance.
+		/// Gets or sets the value at column 3, row 4 of this instance.
 		/// </summary>
-		public pfloat M34 { get { return Column3.Z; } set { Column3.Z = value; } }
+		public pfloat M34 { get { return Column2.W; } set { Column2.W = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 4, column 1 of this instance.
+		/// Gets or sets the value at column 4, row 1 of this instance.
 		/// </summary>
-		public pfloat M41 { get { return Column0.W; } set { Column0.W = value; } }
+		public pfloat M41 { get { return Column3.X; } set { Column3.X = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 4, column 2 of this instance.
+		/// Gets or sets the value at column 4, row 2 of this instance.
 		/// </summary>
-		public pfloat M42 { get { return Column1.W; } set { Column1.W = value; } }
+		public pfloat M42 { get { return Column3.Y; } set { Column3.Y = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 4, column 3 of this instance.
+		/// Gets or sets the value at column 4, row 3 of this instance.
 		/// </summary>
-		public pfloat M43 { get { return Column2.W; } set { Column2.W = value; } }
+		public pfloat M43 { get { return Column3.Z; } set { Column3.Z = value; } }
 
 		/// <summary>
-		/// Gets or sets the value at row 4, column 4 of this instance.
+		/// Gets or sets the value at column 4, row 4 of this instance.
 		/// </summary>
 		public pfloat M44 { get { return Column3.W; } set { Column3.W = value; } }
 
@@ -358,44 +382,85 @@ namespace SceneKit {
 		/// <param name="result">A matrix instance.</param>
 		public static void CreateFromAxisAngle (SCNVector3 axis, pfloat angle, out SCNMatrix4 result)
 		{
-			pfloat cos = (float) System.Math.Cos (-angle);
-			pfloat sin = (float) System.Math.Sin (-angle);
-			pfloat t = 1.0f - cos;
-
 			axis.Normalize ();
 
-			result = new SCNMatrix4 (t * axis.X * axis.X + cos, t * axis.X * axis.Y - sin * axis.Z, t * axis.X * axis.Z + sin * axis.Y, 0.0f,
-			                     t * axis.X * axis.Y + sin * axis.Z, t * axis.Y * axis.Y + cos, t * axis.Y * axis.Z - sin * axis.X, 0.0f,
-			                     t * axis.X * axis.Z - sin * axis.Y, t * axis.Y * axis.Z + sin * axis.X, t * axis.Z * axis.Z + cos, 0.0f,
-			                     0, 0, 0, 1);
+			CreateFromAxisAngle (axis.X, axis.Y, axis.Z, angle, out result);
 		}
 
 		public static void CreateFromAxisAngle (Vector3 axis, float angle, out SCNMatrix4 result)
 		{
-			pfloat cos = (float) System.Math.Cos (-angle);
-			pfloat sin = (float) System.Math.Sin (-angle);
-			pfloat t = 1.0f - cos;
-
 			axis = Vector3.Normalize (axis);
 
-			result = new SCNMatrix4 (t * axis.X * axis.X + cos, t * axis.X * axis.Y - sin * axis.Z, t * axis.X * axis.Z + sin * axis.Y, 0.0f,
-			                     t * axis.X * axis.Y + sin * axis.Z, t * axis.Y * axis.Y + cos, t * axis.Y * axis.Z - sin * axis.X, 0.0f,
-			                     t * axis.X * axis.Z - sin * axis.Y, t * axis.Y * axis.Z + sin * axis.X, t * axis.Z * axis.Z + cos, 0.0f,
-			                     0, 0, 0, 1);
+			CreateFromAxisAngle (axis.X, axis.Y, axis.Z, angle, out result);
 		}
 
 		public static void CreateFromAxisAngle (Vector3d axis, double angle, out SCNMatrix4 result)
 		{
-			double cos = System.Math.Cos (-angle);
-			double sin = System.Math.Sin (-angle);
-			double t = 1.0f - cos;
-
 			axis.Normalize ();
 
-			result = new SCNMatrix4 ((pfloat) (t * axis.X * axis.X + cos), (pfloat) (t * axis.X * axis.Y - sin * axis.Z), (pfloat) (t * axis.X * axis.Z + sin * axis.Y), (pfloat) (0.0f),
-			         (pfloat) ( t * axis.X * axis.Y + sin * axis.Z), (pfloat) (t * axis.Y * axis.Y + cos), (pfloat) (t * axis.Y * axis.Z - sin * axis.X), (pfloat) 0.0f,
-			         (pfloat) (t * axis.X * axis.Z - sin * axis.Y), (pfloat) (t * axis.Y * axis.Z + sin * axis.X), (pfloat) (t * axis.Z * axis.Z + cos), (pfloat) 0.0f,
-			         0, 0, 0, 1);
+			CreateFromAxisAngle (axis.X, axis.Y, axis.Z, angle, out result);
+		}
+
+		/// <summary>
+		/// Build a rotation matrix from the specified axis/angle rotation.
+		/// </summary>
+		/// <param name="x">The x part of the normalized axis to rotate about.</param>
+		/// <param name="y">The y part of the normalized axis to rotate about.</param>
+		/// <param name="z">The z part of the normalized axis to rotate about.</param>
+		/// <param name="angle">Angle in radians to rotate counter-clockwise (looking in the direction of the given axis).</param>
+		/// <param name="result">A matrix instance.</param>
+		static void CreateFromAxisAngle (float x, float y, float z, float angle, out SCNMatrix4 result)
+		{
+			var cos = MathF.Cos (-angle);
+			var sin = MathF.Sin (-angle);
+			var t = 1.0f - cos;
+
+			var m11 = t * x * x + cos;
+			var m12 = t * x * y - sin * z;
+			var m13 = t * x * z + sin * y;
+			var m21 = t * x * y + sin * z;
+			var m22 = t * y * y + cos;
+			var m23 = t * y * z - sin * x;
+			var m31 = t * x * z - sin * y;
+			var m32 = t * y * z + sin * x;
+			var m33 = t * z * z + cos;
+
+			result = new SCNMatrix4 (
+				 m11,  m21,  m31, 0.0f,
+				 m12,  m22,  m32, 0.0f,
+				 m13,  m23,  m33, 0.0f,
+				0.0f, 0.0f, 0.0f, 1.0f);
+		}
+
+		/// <summary>
+		/// Build a rotation matrix from the specified axis/angle rotation.
+		/// </summary>
+		/// <param name="x">The x part of the normalized axis to rotate about.</param>
+		/// <param name="y">The y part of the normalized axis to rotate about.</param>
+		/// <param name="z">The z part of the normalized axis to rotate about.</param>
+		/// <param name="angle">Angle in radians to rotate counter-clockwise (looking in the direction of the given axis).</param>
+		/// <param name="result">A matrix instance.</param>
+		static void CreateFromAxisAngle (double x, double y, double z, double angle, out SCNMatrix4 result)
+		{
+			var cos = Math.Cos (-angle);
+			var sin = Math.Sin (-angle);
+			var t = 1.0f - cos;
+
+			var m11 = (pfloat) (t * x * x + cos);
+			var m12 = (pfloat) (t * x * y - sin * z);
+			var m13 = (pfloat) (t * x * z + sin * y);
+			var m21 = (pfloat) (t * x * y + sin * z);
+			var m22 = (pfloat) (t * y * y + cos);
+			var m23 = (pfloat) (t * y * z - sin * x);
+			var m31 = (pfloat) (t * x * z - sin * y);
+			var m32 = (pfloat) (t * y * z + sin * x);
+			var m33 = (pfloat) (t * z * z + cos);
+
+			result = new SCNMatrix4 (
+				 m11,  m21,  m31, 0.0f,
+				 m12,  m22,  m32, 0.0f,
+				 m13,  m23,  m33, 0.0f,
+				0.0f, 0.0f, 0.0f, 1.0f);
 		}
 
 		/// <summary>
@@ -425,11 +490,11 @@ namespace SceneKit {
 			pfloat cos = (pfloat) System.Math.Cos (angle);
 			pfloat sin = (pfloat) System.Math.Sin (angle);
 
-			result = new SCNMatrix4 ();
-			result.Row0 = SCNVector4.UnitX;
-			result.Row1 = new SCNVector4 (0.0f, cos, sin, 0.0f);
-			result.Row2 = new SCNVector4 (0.0f, -sin, cos, 0.0f);
-			result.Row3 = SCNVector4.UnitW;
+			result = new SCNMatrix4 (
+				1,    0,    0,    0,
+				0,  cos, -sin,    0,
+				0,  sin,  cos,    0,
+				0,    0,    0,    1);
 		}
 
 		/// <summary>
@@ -454,11 +519,11 @@ namespace SceneKit {
 			pfloat cos = (pfloat) System.Math.Cos (angle);
 			pfloat sin = (pfloat) System.Math.Sin (angle);
 
-			result = new SCNMatrix4 ();
-			result.Row0 = new SCNVector4 (cos, 0.0f, -sin, 0.0f);
-			result.Row1 = SCNVector4.UnitY;
-			result.Row2 = new SCNVector4 (sin, 0.0f, cos, 0.0f);
-			result.Row3 = SCNVector4.UnitW;
+			result = new SCNMatrix4 (
+				 cos,    0,  sin,    0,
+				   0,    1,    0,    0,
+				-sin,    0,  cos,    0,
+				   0,    0,    0,    1);
 		}
 
 		/// <summary>
@@ -483,11 +548,11 @@ namespace SceneKit {
 			pfloat cos = (pfloat) System.Math.Cos (angle);
 			pfloat sin = (pfloat) System.Math.Sin (angle);
 
-			result = new SCNMatrix4 ();
-			result.Row0 = new SCNVector4 (cos, sin, 0.0f, 0.0f);
-			result.Row1 = new SCNVector4 (-sin, cos, 0.0f, 0.0f);
-			result.Row2 = SCNVector4.UnitZ;
-			result.Row3 = SCNVector4.UnitW;
+			result = new SCNMatrix4 (
+				 cos, -sin,    0,    0,
+				 sin,  cos,    0,    0,
+				   0,    0,    1,    0,
+				   0,    0,    0,    1);
 		}
 
 		/// <summary>
@@ -515,8 +580,11 @@ namespace SceneKit {
 		/// <param name="result">The resulting SCNMatrix4 instance.</param>
 		public static void CreateTranslation (pfloat x, pfloat y, pfloat z, out SCNMatrix4 result)
 		{
-			result = Identity;
-			result.Row3 = new SCNVector4 (x, y, z, 1);
+			result = new SCNMatrix4 (
+				1, 0, 0, x,
+				0, 1, 0, y,
+				0, 0, 1, z,
+				0, 0, 0, 1);
 		}
 
 		/// <summary>
@@ -526,8 +594,7 @@ namespace SceneKit {
 		/// <param name="result">The resulting SCNMatrix4 instance.</param>
 		public static void CreateTranslation (ref SCNVector3 vector, out SCNMatrix4 result)
 		{
-			result = Identity;
-			result.Row3 = new SCNVector4 (vector.X, vector.Y, vector.Z, 1);
+			CreateTranslation (vector.X, vector.Y, vector.Z, out result);
 		}
 
 		/// <summary>
@@ -743,10 +810,11 @@ namespace SceneKit {
 			pfloat c = -(zFar + zNear) / (zFar - zNear);
 			pfloat d = -(2.0f * zFar * zNear) / (zFar - zNear);
 
-			result = new SCNMatrix4 (x, 0, 0, 0,
-			                     0, y, 0, 0,
-			                     a, b, c, -1,
-			                     0, 0, d, 0);
+			result = new SCNMatrix4 (
+				x,  0,  a,  0,
+				0,  y,  b,  0,
+				0,  0,  c,  d,
+				0,  0, -1,  0);
 		}
 
 		/// <summary>
@@ -807,12 +875,11 @@ namespace SceneKit {
 		/// <returns>A scaling matrix</returns>
 		public static SCNMatrix4 Scale (pfloat x, pfloat y, pfloat z)
 		{
-			var result = new SCNMatrix4 ();
-			result.Row0 = SCNVector4.UnitX * x;
-			result.Row1 = SCNVector4.UnitY * y;
-			result.Row2 = SCNVector4.UnitZ * z;
-			result.Row3 = SCNVector4.UnitW;
-			return result;
+			return new SCNMatrix4 (
+				x, 0, 0, 0,
+				0, y, 0, 0,
+				0, 0, z, 0,
+				0, 0, 0, 1);
 		}
 
 		#endregion
@@ -865,10 +932,11 @@ namespace SceneKit {
 			SCNVector3 x = SCNVector3.Normalize (SCNVector3.Cross (up, z));
 			SCNVector3 y = SCNVector3.Normalize (SCNVector3.Cross (z, x));
 
-			SCNMatrix4 rot = new SCNMatrix4 (new SCNVector4 (x.X, y.X, z.X, 0.0f),
-			                             new SCNVector4 (x.Y, y.Y, z.Y, 0.0f),
-			                             new SCNVector4 (x.Z, y.Z, z.Z, 0.0f),
-			                             SCNVector4.UnitW);
+			SCNMatrix4 rot = new SCNMatrix4 (
+					 x.X,  x.Y,  x.Z, 0.0f,
+					 y.X,  y.Y,  y.Z, 0.0f,
+					 z.X,  z.Y,  z.Z, 0.0f,
+					0.0f, 0.0f, 0.0f, 1.0f);
 
 			SCNMatrix4 trans = SCNMatrix4.CreateTranslation (-eye);
 
@@ -898,43 +966,92 @@ namespace SceneKit {
 		#region Multiply Functions
 
 		/// <summary>
-		/// Multiplies two instances.
+		/// Combines two transformation matrices.
 		/// </summary>
-		/// <param name="left">The left operand of the multiplication.</param>
-		/// <param name="right">The right operand of the multiplication.</param>
-		/// <returns>A new instance that is the result of the multiplication</returns>
-		public static SCNMatrix4 Mult (SCNMatrix4 left, SCNMatrix4 right)
+#if XAMCORE_5_0
+		/// <remarks>
+		/// Combining two transformation matrices means using matrix multiplication to multiply them in the reverse order (secondTransformation * firstTransformation).
+		/// </remarks>
+		/// <param name="firstTransformation">The first transformation of the combination.</param>
+		/// <param name="secondTransformation">The second transformation of the combination.</param>
+#else
+		/// <remarks>
+		/// Combining two transformation matrices means using matrix multiplication to multiply them in the reverse order (right * left).
+		/// </remarks>
+		/// <param name="left">The first transformation of the combination.</param>
+		/// <param name="right">The second transformation of the combination.</param>
+#endif
+		/// <returns>A new instance that is the result of the combination</returns>
+#if XAMCORE_5_0
+		public static SCNMatrix4 Mult (SCNMatrix4 firstTransformation, SCNMatrix4 secondTransformation)
+#else
+		public static SCNMatrix4 Mult(SCNMatrix4 left, SCNMatrix4 right)
+#endif
 		{
 			SCNMatrix4 result;
-			Mult (ref left, ref right, out result);
+			// the matrices are reversed: https://github.com/xamarin/xamarin-macios/issues/15094#issuecomment-1139699662
+#if XAMCORE_5_0
+			MatrixMultiply (ref secondTransformation, ref firstTransformation, out result);
+#else
+			MatrixMultiply (ref right, ref left, out result);
+#endif
 			return result;
 		}
 
 		/// <summary>
-		/// Multiplies two instances.
+		/// Combines two transformation matrices.
 		/// </summary>
-		/// <param name="left">The left operand of the multiplication.</param>
-		/// <param name="right">The right operand of the multiplication.</param>
-		/// <param name="result">A new instance that is the result of the multiplication</param>
-		public static void Mult (ref SCNMatrix4 left, ref SCNMatrix4 right, out SCNMatrix4 result)
+#if XAMCORE_5_0
+		/// <remarks>
+		/// Combining two transformation matrices means using matrix multiplication to multiply them in the reverse order (secondTransformation * firstTransformation).
+		/// </remarks>
+		/// <param name="firstTransformation">The first transformation of the combination.</param>
+		/// <param name="secondTransformation">The second transformation of the combination.</param>
+#else
+		/// <remarks>
+		/// Combining two transformation matrices means using matrix multiplication to multiply them in the reverse order (right * left).
+		/// </remarks>
+		/// <param name="left">The first transformation of the combination.</param>
+		/// <param name="right">The second transformation of the combination.</param>
+#endif
+		/// <param name="result">A new instance that is the result of the combination</param>
+#if XAMCORE_5_0
+		public static void Mult (ref SCNMatrix4 firstTransformation, ref SCNMatrix4 secondTransformation, out SCNMatrix4 result)
+#else
+		public static void Mult(ref SCNMatrix4 left, ref SCNMatrix4 right, out SCNMatrix4 result)
+#endif
 		{
-			result = new SCNMatrix4 (
-				left.M11 * right.M11 + left.M12 * right.M21 + left.M13 * right.M31 + left.M14 * right.M41,
-				left.M11 * right.M12 + left.M12 * right.M22 + left.M13 * right.M32 + left.M14 * right.M42,
-				left.M11 * right.M13 + left.M12 * right.M23 + left.M13 * right.M33 + left.M14 * right.M43,
-				left.M11 * right.M14 + left.M12 * right.M24 + left.M13 * right.M34 + left.M14 * right.M44,
-				left.M21 * right.M11 + left.M22 * right.M21 + left.M23 * right.M31 + left.M24 * right.M41,
-				left.M21 * right.M12 + left.M22 * right.M22 + left.M23 * right.M32 + left.M24 * right.M42,
-				left.M21 * right.M13 + left.M22 * right.M23 + left.M23 * right.M33 + left.M24 * right.M43,
-				left.M21 * right.M14 + left.M22 * right.M24 + left.M23 * right.M34 + left.M24 * right.M44,
-				left.M31 * right.M11 + left.M32 * right.M21 + left.M33 * right.M31 + left.M34 * right.M41,
-				left.M31 * right.M12 + left.M32 * right.M22 + left.M33 * right.M32 + left.M34 * right.M42,
-				left.M31 * right.M13 + left.M32 * right.M23 + left.M33 * right.M33 + left.M34 * right.M43,
-				left.M31 * right.M14 + left.M32 * right.M24 + left.M33 * right.M34 + left.M34 * right.M44,
-				left.M41 * right.M11 + left.M42 * right.M21 + left.M43 * right.M31 + left.M44 * right.M41,
-				left.M41 * right.M12 + left.M42 * right.M22 + left.M43 * right.M32 + left.M44 * right.M42,
-				left.M41 * right.M13 + left.M42 * right.M23 + left.M43 * right.M33 + left.M44 * right.M43,
-				left.M41 * right.M14 + left.M42 * right.M24 + left.M43 * right.M34 + left.M44 * right.M44);
+			// the matrices are reversed: https://github.com/xamarin/xamarin-macios/issues/15094#issuecomment-1139699662
+#if XAMCORE_5_0
+			MatrixMultiply (ref secondTransformation, ref firstTransformation, out result);
+#else
+			MatrixMultiply (ref right, ref left, out result);
+#endif
+		}
+
+		// Multiply two matrices in the order you'd expect (left * right).
+		static void MatrixMultiply (ref SCNMatrix4 left, ref SCNMatrix4 right, out SCNMatrix4 result)
+		{
+			result = new SCNMatrix4(
+				left.Column0.X * right.Column0.X + left.Column1.X * right.Column0.Y + left.Column2.X * right.Column0.Z + left.Column3.X * right.Column0.W,
+				left.Column0.X * right.Column1.X + left.Column1.X * right.Column1.Y + left.Column2.X * right.Column1.Z + left.Column3.X * right.Column1.W,
+				left.Column0.X * right.Column2.X + left.Column1.X * right.Column2.Y + left.Column2.X * right.Column2.Z + left.Column3.X * right.Column2.W,
+				left.Column0.X * right.Column3.X + left.Column1.X * right.Column3.Y + left.Column2.X * right.Column3.Z + left.Column3.X * right.Column3.W,
+
+				left.Column0.Y * right.Column0.X + left.Column1.Y * right.Column0.Y + left.Column2.Y * right.Column0.Z + left.Column3.Y * right.Column0.W,
+				left.Column0.Y * right.Column1.X + left.Column1.Y * right.Column1.Y + left.Column2.Y * right.Column1.Z + left.Column3.Y * right.Column1.W,
+				left.Column0.Y * right.Column2.X + left.Column1.Y * right.Column2.Y + left.Column2.Y * right.Column2.Z + left.Column3.Y * right.Column2.W,
+				left.Column0.Y * right.Column3.X + left.Column1.Y * right.Column3.Y + left.Column2.Y * right.Column3.Z + left.Column3.Y * right.Column3.W,
+
+				left.Column0.Z * right.Column0.X + left.Column1.Z * right.Column0.Y + left.Column2.Z * right.Column0.Z + left.Column3.Z * right.Column0.W,
+				left.Column0.Z * right.Column1.X + left.Column1.Z * right.Column1.Y + left.Column2.Z * right.Column1.Z + left.Column3.Z * right.Column1.W,
+				left.Column0.Z * right.Column2.X + left.Column1.Z * right.Column2.Y + left.Column2.Z * right.Column2.Z + left.Column3.Z * right.Column2.W,
+				left.Column0.Z * right.Column3.X + left.Column1.Z * right.Column3.Y + left.Column2.Z * right.Column3.Z + left.Column3.Z * right.Column3.W,
+
+				left.Column0.W * right.Column0.X + left.Column1.W * right.Column0.Y + left.Column2.W * right.Column0.Z + left.Column3.W * right.Column0.W,
+				left.Column0.W * right.Column1.X + left.Column1.W * right.Column1.Y + left.Column2.W * right.Column1.Z + left.Column3.W * right.Column1.W,
+				left.Column0.W * right.Column2.X + left.Column1.W * right.Column2.Y + left.Column2.W * right.Column2.Z + left.Column3.W * right.Column2.W,
+				left.Column0.W * right.Column3.X + left.Column1.W * right.Column3.Y + left.Column2.W * right.Column3.Z + left.Column3.W * right.Column3.W);
 		}
 
 		#endregion
@@ -1102,7 +1219,7 @@ namespace SceneKit {
 		#region public override string ToString()
 
 		/// <summary>
-		/// Returns a System.String that represents the current SCNMatrix44.
+		/// Returns a System.String that represents the current SCNMatrix4.
 		/// </summary>
 		/// <returns></returns>
 		public override string ToString ()

src/SceneKit/SCNVector3.cs

@@ -740,29 +740,53 @@ namespace SceneKit
 
         #region Transform
 
+#if NET
+        /// <summary>Transform a direction vector by the given Matrix
+        /// Assumes the matrix has a right-most column of (0,0,0,1), that is the translation part is ignored.
+        /// </summary>
+        /// <param name="vec">The column vector to transform</param>
+#else
         /// <summary>Transform a direction vector by the given Matrix
         /// Assumes the matrix has a bottom row of (0,0,0,1), that is the translation part is ignored.
         /// </summary>
-        /// <param name="vec">The vector to transform</param>
+        /// <param name="vec">The row vector to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <returns>The transformed vector</returns>
         public static SCNVector3 TransformVector(SCNVector3 vec, SCNMatrix4 mat)
         {
-            SCNVector3 v;
-            v.X = SCNVector3.Dot(vec, new SCNVector3(mat.Column0));
-            v.Y = SCNVector3.Dot(vec, new SCNVector3(mat.Column1));
-            v.Z = SCNVector3.Dot(vec, new SCNVector3(mat.Column2));
+            TransformVector (ref vec, ref mat, out var v);
             return v;
         }
 
+#if NET
+        /// <summary>Transform a direction vector by the given Matrix
+        /// Assumes the matrix has a right-most column of (0,0,0,1), that is the translation part is ignored.
+        /// </summary>
+        /// <param name="vec">The column vector to transform</param>
+#else
         /// <summary>Transform a direction vector by the given Matrix
         /// Assumes the matrix has a bottom row of (0,0,0,1), that is the translation part is ignored.
         /// </summary>
-        /// <param name="vec">The vector to transform</param>
+        /// <param name="vec">The row vector to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <param name="result">The transformed vector</param>
         public static void TransformVector(ref SCNVector3 vec, ref SCNMatrix4 mat, out SCNVector3 result)
         {
+#if NET
+            result.X = vec.X * mat.Row0.X +
+                       vec.Y * mat.Row0.Y +
+                       vec.Z * mat.Row0.Z;
+
+            result.Y = vec.X * mat.Row1.X +
+                       vec.Y * mat.Row1.Y +
+                       vec.Z * mat.Row1.Z;
+
+            result.Z = vec.X * mat.Row2.X +
+                       vec.Y * mat.Row2.Y +
+                       vec.Z * mat.Row2.Z;
+#else
             result.X = vec.X * mat.Row0.X +
                        vec.Y * mat.Row1.X +
                        vec.Z * mat.Row2.X;
@@ -774,6 +798,7 @@ namespace SceneKit
             result.Z = vec.X * mat.Row0.Z +
                        vec.Y * mat.Row1.Z +
                        vec.Z * mat.Row2.Z;
+#endif
         }
 
         /// <summary>Transform a Normal by the given Matrix</summary>
@@ -781,7 +806,11 @@ namespace SceneKit
         /// This calculates the inverse of the given matrix, use TransformNormalInverse if you
         /// already have the inverse to avoid this extra calculation
         /// </remarks>
-        /// <param name="norm">The normal to transform</param>
+#if NET
+        /// <param name="norm">The column-based normal to transform</param>
+#else
+        /// <param name="norm">The row-based normal to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <returns>The transformed normal</returns>
         public static SCNVector3 TransformNormal(SCNVector3 norm, SCNMatrix4 mat)
@@ -795,7 +824,11 @@ namespace SceneKit
         /// This calculates the inverse of the given matrix, use TransformNormalInverse if you
         /// already have the inverse to avoid this extra calculation
         /// </remarks>
-        /// <param name="norm">The normal to transform</param>
+#if NET
+        /// <param name="norm">The column-based normal to transform</param>
+#else
+        /// <param name="norm">The row-based normal to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <param name="result">The transformed normal</param>
         public static void TransformNormal(ref SCNVector3 norm, ref SCNMatrix4 mat, out SCNVector3 result)
@@ -809,15 +842,16 @@ namespace SceneKit
         /// This version doesn't calculate the inverse matrix.
         /// Use this version if you already have the inverse of the desired transform to hand
         /// </remarks>
-        /// <param name="norm">The normal to transform</param>
+#if NET
+        /// <param name="norm">The column-based normal to transform</param>
+#else
+        /// <param name="norm">The row-based normal to transform</param>
+#endif
         /// <param name="invMat">The inverse of the desired transformation</param>
         /// <returns>The transformed normal</returns>
         public static SCNVector3 TransformNormalInverse(SCNVector3 norm, SCNMatrix4 invMat)
         {
-            SCNVector3 n;
-            n.X = SCNVector3.Dot(norm, new SCNVector3(invMat.Row0));
-            n.Y = SCNVector3.Dot(norm, new SCNVector3(invMat.Row1));
-            n.Z = SCNVector3.Dot(norm, new SCNVector3(invMat.Row2));
+        	TransformNormalInverse (ref norm, ref invMat, out var n);
             return n;
         }
 
@@ -826,11 +860,28 @@ namespace SceneKit
         /// This version doesn't calculate the inverse matrix.
         /// Use this version if you already have the inverse of the desired transform to hand
         /// </remarks>
-        /// <param name="norm">The normal to transform</param>
+#if NET
+        /// <param name="norm">The column-based normal to transform</param>
+#else
+        /// <param name="norm">The row-based normal to transform</param>
+#endif
         /// <param name="invMat">The inverse of the desired transformation</param>
         /// <param name="result">The transformed normal</param>
         public static void TransformNormalInverse(ref SCNVector3 norm, ref SCNMatrix4 invMat, out SCNVector3 result)
         {
+#if NET
+            result.X = norm.X * invMat.Column0.X +
+                       norm.Y * invMat.Column0.Y +
+                       norm.Z * invMat.Column0.Z;
+
+            result.Y = norm.X * invMat.Column1.X +
+                       norm.Y * invMat.Column1.Y +
+                       norm.Z * invMat.Column1.Z;
+
+            result.Z = norm.X * invMat.Column2.X +
+                       norm.Y * invMat.Column2.Y +
+                       norm.Z * invMat.Column2.Z;
+#else
             result.X = norm.X * invMat.Row0.X +
                        norm.Y * invMat.Row0.Y +
                        norm.Z * invMat.Row0.Z;
@@ -842,27 +893,49 @@ namespace SceneKit
             result.Z = norm.X * invMat.Row2.X +
                        norm.Y * invMat.Row2.Y +
                        norm.Z * invMat.Row2.Z;
+#endif
         }
 
         /// <summary>Transform a Position by the given Matrix</summary>
-        /// <param name="pos">The position to transform</param>
+#if NET
+        /// <param name="pos">The column-based position to transform</param>
+#else
+        /// <param name="pos">The row-based position to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <returns>The transformed position</returns>
         public static SCNVector3 TransformPosition(SCNVector3 pos, SCNMatrix4 mat)
         {
-            SCNVector3 p;
-            p.X = SCNVector3.Dot(pos, new SCNVector3(mat.Column0)) + mat.Row3.X;
-            p.Y = SCNVector3.Dot(pos, new SCNVector3(mat.Column1)) + mat.Row3.Y;
-            p.Z = SCNVector3.Dot(pos, new SCNVector3(mat.Column2)) + mat.Row3.Z;
+            TransformPosition (ref pos, ref mat, out var p);
             return p;
         }
 
         /// <summary>Transform a Position by the given Matrix</summary>
-        /// <param name="pos">The position to transform</param>
+#if NET
+        /// <param name="pos">The column-based position to transform</param>
+#else
+        /// <param name="pos">The row-based position to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <param name="result">The transformed position</param>
         public static void TransformPosition(ref SCNVector3 pos, ref SCNMatrix4 mat, out SCNVector3 result)
         {
+#if NET
+            result.X = mat.Row0.X * pos.X +
+                       mat.Row0.Y * pos.Y +
+                       mat.Row0.Z * pos.Z +
+                       mat.Row0.W;
+
+            result.Y = mat.Row1.X * pos.X +
+                       mat.Row1.Y * pos.Y +
+                       mat.Row1.Z * pos.Z +
+                       mat.Row1.W;
+
+            result.Z = mat.Row2.X * pos.X +
+                       mat.Row2.Y * pos.Y +
+                       mat.Row2.Z * pos.Z +
+                       mat.Row2.W;
+#else
             result.X = pos.X * mat.Row0.X +
                        pos.Y * mat.Row1.X +
                        pos.Z * mat.Row2.X +
@@ -877,25 +950,29 @@ namespace SceneKit
                        pos.Y * mat.Row1.Z +
                        pos.Z * mat.Row2.Z +
                        mat.Row3.Z;
+#endif
         }
 
         /// <summary>Transform a Vector by the given Matrix</summary>
-        /// <param name="vec">The vector to transform</param>
+#if NET
+        /// <param name="vec">The column vector to transform</param>
+#else
+        /// <param name="vec">The row vector to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <returns>The transformed vector</returns>
         public static SCNVector4 Transform(SCNVector3 vec, SCNMatrix4 mat)
         {
             SCNVector4 v4 = new SCNVector4(vec.X, vec.Y, vec.Z, 1.0f);
-            SCNVector4 result;
-            result.X = SCNVector4.Dot(v4, mat.Column0);
-            result.Y = SCNVector4.Dot(v4, mat.Column1);
-            result.Z = SCNVector4.Dot(v4, mat.Column2);
-            result.W = SCNVector4.Dot(v4, mat.Column3);
-            return result;
+            return SCNVector4.Transform (v4, mat);
         }
 
         /// <summary>Transform a Vector by the given Matrix</summary>
-        /// <param name="vec">The vector to transform</param>
+#if NET
+        /// <param name="vec">The column vector to transform</param>
+#else
+        /// <param name="vec">The row vector to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <param name="result">The transformed vector</param>
         public static void Transform(ref SCNVector3 vec, ref SCNMatrix4 mat, out SCNVector4 result)

src/SceneKit/SCNVector4.cs

@@ -843,25 +843,50 @@ namespace SceneKit
         #region Transform
 
         /// <summary>Transform a Vector by the given Matrix</summary>
-        /// <param name="vec">The vector to transform</param>
+#if NET
+        /// <param name="vec">The column vector to transform</param>
+#else
+        /// <param name="vec">The row vector to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <returns>The transformed vector</returns>
         public static SCNVector4 Transform(SCNVector4 vec, SCNMatrix4 mat)
         {
-            SCNVector4 result;
-            result.X = SCNVector4.Dot(vec, mat.Column0);
-            result.Y = SCNVector4.Dot(vec, mat.Column1);
-            result.Z = SCNVector4.Dot(vec, mat.Column2);
-            result.W = SCNVector4.Dot(vec, mat.Column3);
+            Transform(ref vec, ref mat, out var result);
             return result;
         }
 
-        /// <summary>Transform a Vector by the given Matrix</summary>
-        /// <param name="vec">The vector to transform</param>
+        /// <summary>Transform a Vector by the given Matrix.</summary>
+#if NET
+        /// <param name="vec">The column vector to transform</param>
+#else
+        /// <param name="vec">The row vector to transform</param>
+#endif
         /// <param name="mat">The desired transformation</param>
         /// <param name="result">The transformed vector</param>
         public static void Transform(ref SCNVector4 vec, ref SCNMatrix4 mat, out SCNVector4 result)
         {
+#if NET
+            result.X = vec.X * mat.Column0.X +
+                       vec.Y * mat.Column1.X +
+                       vec.Z * mat.Column2.X +
+                       vec.W * mat.Column3.X;
+
+            result.Y = vec.X * mat.Column0.Y +
+                       vec.Y * mat.Column1.Y +
+                       vec.Z * mat.Column2.Y +
+                       vec.W * mat.Column3.Y;
+
+            result.Z = vec.X * mat.Column0.Z +
+                       vec.Y * mat.Column1.Z +
+                       vec.Z * mat.Column2.Z +
+                       vec.W * mat.Column3.Z;
+
+            result.W = vec.X * mat.Column0.W +
+                       vec.Y * mat.Column1.W +
+                       vec.Z * mat.Column2.W +
+                       vec.W * mat.Column3.W;
+#else
             result.X = vec.X * mat.Row0.X +
                        vec.Y * mat.Row1.X +
                        vec.Z * mat.Row2.X +
@@ -881,6 +906,7 @@ namespace SceneKit
                        vec.Y * mat.Row1.W +
                        vec.Z * mat.Row2.W +
                        vec.W * mat.Row3.W;
+#endif
         }
 
         #endregion

src/WebKit/DomCssRuleList.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 namespace WebKit {
 	
 	public partial class DomCssRuleList {

src/WebKit/DomHelpers.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 using ObjCRuntime;
 using Foundation;

src/WebKit/DomNode.cs

@@ -21,6 +21,8 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 using System;
 using System.Runtime.Versioning;
 
@@ -77,8 +79,8 @@ namespace WebKit {
 		public DomEventListener AddEventListener (string type, DomEventListenerHandler handler, bool useCapture)
 #endif
 		{
-			if (handler == null)
-				throw new ArgumentNullException ("handler");
+			if (handler is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (handler));
 			var obj = new DomNodeEventProxy (this, handler);
 			AddEventListener (type, obj, useCapture);
 			return obj;
@@ -90,8 +92,8 @@ namespace WebKit {
 		public DomEventListener AddEventListener (string type, Action<DomEvent> callback, bool useCapture)
 #endif
 		{
-			if (callback == null)
-				throw new ArgumentNullException ("callback");
+			if (callback is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (callback));
 			var obj = new DomNodeEventProxy2 (callback);
 			AddEventListener (type, obj, useCapture);
 			return obj;

src/WebKit/Enumerators.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -24,15 +26,19 @@ namespace WebKit {
 
 		public T Current {
 			get {
+				if (_container is null)
+					throw new ObjectDisposedException (nameof (_container));
 				return _container [_index];
 			}
 		}
 
-		object IEnumerator.Current {
+		object? IEnumerator.Current {
 			get { return ((IEnumerator<T>) this).Current; }
 		}
 
 		public bool MoveNext () {
+			if (_container is null)
+				throw new ObjectDisposedException (nameof (_container));
 			return ++_index < _container.Count;
 		}
 
@@ -40,7 +46,7 @@ namespace WebKit {
 			_index = -1;
 		}
 
-		IIndexedContainer<T> _container;
+		IIndexedContainer<T>? _container;
 		int _index;
 	}
 

src/WebKit/Indexers.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 namespace WebKit {
 	
 	public partial class DomCssRuleList {

src/WebKit/WebKit.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 using Foundation;
 
 namespace WebKit {

src/WebKit/WebNavigationPolicyEventArgs.cs

@@ -6,6 +6,8 @@
 //
 // Copyright 2013 Xamarin Inc
 
+#nullable enable
+
 using System;
 
 using Foundation;
@@ -27,14 +29,14 @@ namespace WebKit {
 			get { return (WebNavigationType)((NSNumber)ActionInformation[WebPolicyDelegate.WebActionNavigationTypeKey]).Int32Value; }
 		}
 
-		public NSDictionary ElementInfo {
+		public NSDictionary? ElementInfo {
 			get { return ActionInformation[WebPolicyDelegate.WebActionElementKey] as NSDictionary; }
 		}
 
 		public WebActionMouseButton MouseButton {
 			get {
 				var number = ActionInformation[WebPolicyDelegate.WebActionButtonKey] as NSNumber;
-				if (number == null) {
+				if (number is null) {
 					return WebActionMouseButton.None;
 				}
 
@@ -46,7 +48,7 @@ namespace WebKit {
 			get { return ((NSNumber)ActionInformation[WebPolicyDelegate.WebActionModifierFlagsKey]).UInt32Value; }
 		}
 
-		public NSUrl OriginalUrl {
+		public NSUrl? OriginalUrl {
 			get { return ActionInformation[WebPolicyDelegate.WebActionOriginalUrlKey] as NSUrl; }
 		}
 	}

src/WebKit/WebPolicyDelegate.cs

@@ -20,6 +20,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using Foundation;
 using ObjCRuntime;
@@ -33,24 +36,24 @@ namespace WebKit {
 		
 		public static void DecideUse (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("token");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selUse);
 		}
 		
 		public static void DecideDownload (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selDownload);
 		}
 		
 		public static void DecideIgnore (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selIgnore);
 		}

src/WebKit/WebView.cs

@@ -20,6 +20,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using Foundation;
 using ObjCRuntime;
@@ -33,24 +36,24 @@ namespace WebKit {
 		
 		public static void DecideUse (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("token");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selUse);
 		}
 		
 		public static void DecideDownload (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selDownload);
 		}
 		
 		public static void DecideIgnore (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selIgnore);
 		}

src/passkit.cs

@@ -81,6 +81,7 @@ namespace PassKit {
 		PKPass[] GetPasses ();
 
 		[Export ("passWithPassTypeIdentifier:serialNumber:")]
+		[return: NullAllowed]
 		PKPass GetPass (string identifier, string serialNumber);
 
 		[iOS (8,0)]
@@ -264,7 +265,7 @@ namespace PassKit {
 		[Deprecated (PlatformName.iOS, 9, 0, message: "Use 'ShippingContact' instead.")]
 		ABRecord ShippingAddress { get; }
 
-		[Export ("shippingMethod", ArgumentSemantic.Strong)]
+		[NullAllowed, Export ("shippingMethod", ArgumentSemantic.Strong)]
 		PKShippingMethod ShippingMethod { get; }
 
 		
@@ -813,7 +814,7 @@ namespace PassKit {
 		[Export ("initWithData:error:")]
 		NativeHandle Constructor (NSData data, out NSError error);
 
-		[Export ("authenticationToken", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("authenticationToken", ArgumentSemantic.Copy)]
 		string AuthenticationToken { get; }
 
 		[NoWatch]
@@ -838,16 +839,17 @@ namespace PassKit {
 		[Export ("passURL", ArgumentSemantic.Copy)]
 		NSUrl PassUrl { get; }
 
-		[Export ("relevantDate", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("relevantDate", ArgumentSemantic.Copy)]
 		NSDate RelevantDate { get; }
 
 		[Export ("serialNumber", ArgumentSemantic.Copy)]
 		string SerialNumber { get; }
 
-		[Export ("webServiceURL", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("webServiceURL", ArgumentSemantic.Copy)]
 		NSUrl WebServiceUrl { get; }
 
 		[Export ("localizedValueForFieldKey:")]
+		[return: NullAllowed]
 		NSObject GetLocalizedValue (NSString key); // TODO: Should be enum for PKPassLibraryUserInfoKey
 
 #if !NET
@@ -857,7 +859,7 @@ namespace PassKit {
 #endif
 
 		[iOS (7,0)]
-		[Export ("userInfo", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("userInfo", ArgumentSemantic.Copy)]
 		NSDictionary UserInfo { get; }
 
 		[iOS (8,0)]
@@ -1334,7 +1336,7 @@ namespace PassKit {
 		[Export ("status", ArgumentSemantic.Assign)]
 		PKPaymentAuthorizationStatus Status { get; set; }
 
-		[Export ("errors", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("errors", ArgumentSemantic.Copy)]
 		NSError[] Errors { get; set; }
 	}
 
@@ -1372,7 +1374,7 @@ namespace PassKit {
 		[Export ("shippingMethods", ArgumentSemantic.Copy)]
 		PKShippingMethod[] ShippingMethods { get; set; }
 
-		[Export ("errors", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("errors", ArgumentSemantic.Copy)]
 		NSError[] Errors { get; set; }
 	}
 
@@ -1400,7 +1402,7 @@ namespace PassKit {
 		NativeHandle Constructor ([NullAllowed] NSError[] errors, PKPaymentSummaryItem [] paymentSummaryItems);
 
 		[Watch (6,0), iOS (13,0)]
-		[Export ("errors", ArgumentSemantic.Copy)]
+		[NullAllowed, Export ("errors", ArgumentSemantic.Copy)]
 		NSError [] Errors { get; set; }
 
 		// inlined

system-dependencies.sh

@@ -379,8 +379,6 @@ function install_specific_xcode () {
 		done
 	fi
 
-	log "Executing '$SUDO xcode-select -s $XCODE_DEVELOPER_ROOT'"
-	$SUDO xcode-select -s $XCODE_DEVELOPER_ROOT
 	log "Clearing xcrun cache..."
 	xcrun -k
 
@@ -494,20 +492,6 @@ function check_specific_xcode () {
 		return
 	fi
 
-	if test -z "$1"; then
-		local XCODE_SELECT=$(xcode-select -p)
-		if [[ "x$XCODE_SELECT" != "x$XCODE_DEVELOPER_ROOT" ]]; then
-			if ! test -z $PROVISION_XCODE; then
-				log "Executing '$SUDO xcode-select -s $XCODE_DEVELOPER_ROOT'"
-				$SUDO xcode-select -s $XCODE_DEVELOPER_ROOT
-				log "Clearing xcrun cache..."
-				xcrun -k
-			else
-				fail "'xcode-select -p' does not point to $XCODE_DEVELOPER_ROOT, it points to $XCODE_SELECT. Execute 'make fix-xcode-select' to fix."
-			fi
-		fi
-	fi
-
 	ok "Found Xcode $XCODE_ACTUAL_VERSION in $XCODE_ROOT"
 }
 

tests/Makefile

@@ -12,7 +12,6 @@ endif
 
 MTOUCH=$(IOS_DESTDIR)/$(MONOTOUCH_PREFIX)/bin/mtouch
 
-export MD_APPLE_SDK_ROOT=$(abspath $(XCODE_DEVELOPER_ROOT)/../..)
 export MD_MTOUCH_SDK_ROOT=$(IOS_DESTDIR)/$(MONOTOUCH_PREFIX)
 export MSBUILD_EXE_PATH=$(MONO_PREFIX)/lib/mono/msbuild/15.0/bin/MSBuild.dll
 export TargetFrameworkFallbackSearchPaths=$(IOS_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild-frameworks

tests/bindings-test/StructsAndEnums.cs

@@ -3,6 +3,7 @@ using System.Runtime.InteropServices;
 
 using Foundation;
 using ObjCRuntime;
+using SceneKit;
 
 #if NET
 using MatrixFloat2x2 = global::CoreGraphics.NMatrix2;
@@ -16,6 +17,16 @@ using MatrixFloat4x3 = global::OpenTK.NMatrix4x3;
 using MatrixFloat4x4 = global::OpenTK.NMatrix4;
 #endif
 
+#if __MACOS__
+#if NET
+using pfloat = System.Runtime.InteropServices.NFloat;
+#else
+using pfloat = System.nfloat;
+#endif
+#else
+using pfloat = System.Single;
+#endif
+
 public static class LibTest {
 	[DllImport ("__Internal")]
 	public static extern int theUltimateAnswer ();
@@ -126,5 +137,14 @@ namespace Bindings.Test
 				r3c0, r3c1, r3c2, r3c3);
 		}
 #endif
+
+		[DllImport ("__Internal")]
+		public static extern SCNMatrix4 x_SCNMatrix4MakeTranslation (pfloat tx, pfloat ty, pfloat tz);
+
+		[DllImport ("__Internal")]
+		public static extern SCNMatrix4 x_SCNMatrix4MakeScale (pfloat tx, pfloat ty, pfloat tz);
+
+		[DllImport ("__Internal")]
+		public static extern SCNMatrix4 x_SCNMatrix4Translate (SCNMatrix4 m, pfloat tx, pfloat ty, pfloat tz);
 	}
 }

tests/common/mac/project_building.mk

@@ -10,7 +10,6 @@ SOURCES = $(TEST_SRC) \
 # Everything that would invalidate a build
 ALL_SOURCE_FILES = $(TEST_SRC) $(SOURCES) $(EXTRA_FILES) Makefile
 
-export MD_APPLE_SDK_ROOT=$(shell dirname `dirname $(XCODE_DEVELOPER_ROOT)`)
 export TargetFrameworkFallbackSearchPaths=$(MAC_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild-frameworks
 export MSBuildExtensionsPathFallbackPathsOverride=$(MAC_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild
 export XamarinMacFrameworkRoot=$(MAC_DESTDIR)/Library/Frameworks/Xamarin.Mac.framework/Versions/Current

tests/common/shared-dotnet.csproj

@@ -53,6 +53,9 @@
 
 		<!-- XAMCORE_3_0 is always defined for .NET -->
 		<DefineConstants>$(DefineConstants);XAMCORE_3_0</DefineConstants>
+
+		<!-- Don't show warnings about platform availability -->
+		<NoWarn Condition="'$(IncludeCS1416Warnigs)' != 'true'">CA1416;$(NoWarn)</NoWarn>
 	</PropertyGroup>
 
 	<ItemGroup>

tests/dotnet/size-comparison/common.mk

@@ -33,7 +33,6 @@ report:
 
 COMMON_ARGS=/p:Platform=iPhone /p:Configuration=Release $(MSBUILD_VERBOSITY)
 
-build-oldnet: export MD_APPLE_SDK_ROOT=$(abspath $(XCODE_DEVELOPER_ROOT)/../..)
 build-oldnet: export MD_MTOUCH_SDK_ROOT=$(IOS_DESTDIR)/$(MONOTOUCH_PREFIX)
 build-oldnet: export MSBUILD_EXE_PATH=$(MONO_PREFIX)/lib/mono/msbuild/15.0/bin/MSBuild.dll
 build-oldnet: export TargetFrameworkFallbackSearchPaths=$(IOS_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild-frameworks

tests/mac-binding-project/Makefile

@@ -1,7 +1,6 @@
 TOP=../..
 include $(TOP)/Make.config
 
-export MD_APPLE_SDK_ROOT=$(shell dirname `dirname $(XCODE_DEVELOPER_ROOT)`)
 export TargetFrameworkFallbackSearchPaths=$(MAC_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild-frameworks
 export MSBuildExtensionsPathFallbackPathsOverride=$(MAC_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild
 export XamarinMacFrameworkRoot=$(MAC_DESTDIR)/Library/Frameworks/Xamarin.Mac.framework/Versions/Current

tests/mmp-regression/Makefile

@@ -4,8 +4,6 @@ include $(TOP)/Make.config
 
 MMP=$(MAC_DESTDIR)/Library/Frameworks/Xamarin.Mac.framework/Versions/Current/bin/mmp
 
-export MD_APPLE_SDK_ROOT:=$(abspath $(XCODE_DEVELOPER_ROOT)/../..)
-
 ifdef TESTS_USE_SYSTEM
 export TargetFrameworkFallbackSearchPaths=/Library/Frameworks/Mono.framework/External/xbuild-frameworks
 export MSBuildExtensionsPathFallbackPathsOverride=/Library/Frameworks/Mono.framework/External/xbuild

tests/monotouch-test/Asserts.cs

@@ -1,8 +1,15 @@
 using System;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Text;
+
 #if !__WATCHOS__
 using ModelIO;
 using MetalPerformanceShaders;
 #endif
+#if HAS_SCENEKIT
+using SceneKit;
+#endif
 
 #if NET
 using System.Numerics;
@@ -31,6 +38,16 @@ using MatrixDouble4x4 = global::OpenTK.NMatrix4d;
 using VectorDouble3 = global::OpenTK.NVector3d;
 #endif
 
+#if __MACOS__
+#if NET
+using pfloat = System.Runtime.InteropServices.NFloat;
+#else
+using pfloat = System.nfloat;
+#endif
+#else
+using pfloat = System.Single;
+#endif
+
 using NUnit.Framework;
 
 public static class Asserts
@@ -714,4 +731,285 @@ public static class Asserts
 		AreEqual (expected.M34, actual.M34, $"{message} (M34) expected: {expected} actual: {actual}");
 	}
 #endregion
+
+#if HAS_SCENEKIT
+	public static void AreEqual (SCNVector3 expected, SCNVector3 actual, string message)
+	{
+		if (AreEqual (expected.X, actual.X, out var dX) &
+			AreEqual (expected.Y, actual.Y, out var dY) &
+			AreEqual (expected.Z, actual.Z, out var dZ))
+			return;
+
+		var diffString = $"({dX}, {dY}, {dZ})";
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+	public static void AreEqual (SCNVector3 expected, SCNVector3 actual, pfloat delta, string message)
+	{
+		if (AreEqual (expected.X, actual.X, delta, out var dX) &
+			AreEqual (expected.Y, actual.Y, delta, out var dY) &
+			AreEqual (expected.Z, actual.Z, delta, out var dZ))
+			return;
+
+		var diffString = $"({dX}, {dY}, {dZ})";
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+	public static void AreEqual (SCNVector4 expected, SCNVector4 actual, string message)
+	{
+		if (AreEqual (expected.X, actual.X, out var dX) &
+			AreEqual (expected.Y, actual.Y, out var dY) &
+			AreEqual (expected.Z, actual.Z, out var dZ) &
+			AreEqual (expected.W, actual.W, out var dW))
+			return;
+
+		var diffString = $"({dX}, {dY}, {dZ}, {dW})";
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+
+	public static void AreEqual (SCNVector4 expected, SCNVector4 actual, pfloat delta, string message)
+	{
+		if (AreEqual (expected.X, actual.X, delta, out var dX) &
+			AreEqual (expected.Y, actual.Y, delta, out var dY) &
+			AreEqual (expected.Z, actual.Z, delta, out var dZ) &
+			AreEqual (expected.W, actual.W, delta, out var dW))
+			return;
+
+		var diffString = $"({dX}, {dY}, {dZ}, {dW})";
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+	public static void AreEqual (SCNQuaternion expected, SCNQuaternion actual, string message)
+	{
+		if (AreEqual (expected.X, actual.X, out var dX) &
+			AreEqual (expected.Y, actual.Y, out var dY) &
+			AreEqual (expected.Z, actual.Z, out var dZ) &
+			AreEqual (expected.W, actual.W, out var dW))
+			return;
+
+		var diffString = $"[{dX}, {dY}, {dZ}, {dW}]";
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+	public static void AreEqual (SCNQuaternion expected, SCNQuaternion actual, pfloat delta, string message)
+	{
+		if (AreEqual (expected.X, actual.X, delta, out var dX) &
+			AreEqual (expected.Y, actual.Y, delta, out var dY) &
+			AreEqual (expected.Z, actual.Z, delta, out var dZ) &
+			AreEqual (expected.W, actual.W, delta, out var dW))
+			return;
+
+		var diffString = $"[{dX}, {dY}, {dZ}, {dW}]";
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+	public static void AreEqual (SCNMatrix4 expected, SCNMatrix4 actual, string message)
+	{
+		if (AreEqual (expected.M11, actual.M11, out var d11) &
+			AreEqual (expected.M21, actual.M21, out var d21) &
+			AreEqual (expected.M31, actual.M31, out var d31) &
+			AreEqual (expected.M41, actual.M41, out var d41) &
+			AreEqual (expected.M12, actual.M12, out var d12) &
+			AreEqual (expected.M22, actual.M22, out var d22) &
+			AreEqual (expected.M32, actual.M32, out var d32) &
+			AreEqual (expected.M42, actual.M42, out var d42) &
+			AreEqual (expected.M13, actual.M13, out var d13) &
+			AreEqual (expected.M23, actual.M23, out var d23) &
+			AreEqual (expected.M33, actual.M33, out var d33) &
+			AreEqual (expected.M43, actual.M43, out var d43) &
+			AreEqual (expected.M14, actual.M14, out var d14) &
+			AreEqual (expected.M24, actual.M24, out var d24) &
+			AreEqual (expected.M34, actual.M34, out var d34) &
+			AreEqual (expected.M44, actual.M44, out var d44)) {
+
+			var size = Marshal.SizeOf (typeof (SCNMatrix4));
+			unsafe {
+				byte* e = (byte*) (void*) &expected;
+				byte* a = (byte*) (void*) &actual;
+				AreEqual (e, a, size, message);
+			}
+			return;
+		}
+
+		var actualString = actual.ToString ();
+
+		var expectedString = expected.ToString ();
+
+		var diffRow1 = $"({d11}, {d12}, {d13}, {d14})";
+		var diffRow2 = $"({d21}, {d22}, {d23}, {d24})";
+		var diffRow3 = $"({d31}, {d32}, {d33}, {d34})";
+		var diffRow4 = $"({d41}, {d42}, {d43}, {d44})";
+		var diffString = $"{diffRow1}\n{diffRow2}\n{diffRow3}\n{diffRow4}";
+
+		var msg = $"{message}\nExpected:\n{expected}\nActual:\n{actual}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+	public static void AreEqual (SCNMatrix4 expected, SCNMatrix4 actual, pfloat delta, string message)
+	{
+		if (AreEqual (expected.M11, actual.M11, delta, out var d11) &
+			AreEqual (expected.M21, actual.M21, delta, out var d21) &
+			AreEqual (expected.M31, actual.M31, delta, out var d31) &
+			AreEqual (expected.M41, actual.M41, delta, out var d41) &
+			AreEqual (expected.M12, actual.M12, delta, out var d12) &
+			AreEqual (expected.M22, actual.M22, delta, out var d22) &
+			AreEqual (expected.M32, actual.M32, delta, out var d32) &
+			AreEqual (expected.M42, actual.M42, delta, out var d42) &
+			AreEqual (expected.M13, actual.M13, delta, out var d13) &
+			AreEqual (expected.M23, actual.M23, delta, out var d23) &
+			AreEqual (expected.M33, actual.M33, delta, out var d33) &
+			AreEqual (expected.M43, actual.M43, delta, out var d43) &
+			AreEqual (expected.M14, actual.M14, delta, out var d14) &
+			AreEqual (expected.M24, actual.M24, delta, out var d24) &
+			AreEqual (expected.M34, actual.M34, delta, out var d34) &
+			AreEqual (expected.M44, actual.M44, delta, out var d44))
+			return;
+
+		var actualString = actual.ToString ();
+		var expectedString = expected.ToString ();
+
+		var diffRow1 = $"({d11}, {d12}, {d13}, {d14})";
+		var diffRow2 = $"({d21}, {d22}, {d23}, {d24})";
+		var diffRow3 = $"({d31}, {d32}, {d33}, {d34})";
+		var diffRow4 = $"({d41}, {d42}, {d43}, {d44})";
+		var diffString = $"{diffRow1}\n{diffRow2}\n{diffRow3}\n{diffRow4}";
+
+		var msg = $"{message}\nExpected:\n{expectedString}\nActual:\n{actualString}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+
+
+	// The m## arguments correspond with the M## fields in SCNMatrix4
+	// For .NET this means the first four values are the first column (and the first row for legacy Xamarin).
+	public static void AreEqual (SCNMatrix4 actual, string message,
+		pfloat m11, pfloat m12, pfloat m13, pfloat m14,
+		pfloat m21, pfloat m22, pfloat m23, pfloat m24,
+		pfloat m31, pfloat m32, pfloat m33, pfloat m34,
+		pfloat m41, pfloat m42, pfloat m43, pfloat m44)
+	{
+		AreEqual (actual, message,
+			m11, m12, m13, m14,
+			m21, m22, m23, m24,
+			m31, m32, m33, m34,
+			m41, m42, m43, m44,
+			delta: 0);
+	}
+
+	// The m## arguments correspond with the M## fields in SCNMatrix4
+	// For .NET this means the first four values are the first column (and the first row for legacy Xamarin).
+	public static void AreEqual (SCNMatrix4 actual, string message,
+		pfloat m11, pfloat m12, pfloat m13, pfloat m14,
+		pfloat m21, pfloat m22, pfloat m23, pfloat m24,
+		pfloat m31, pfloat m32, pfloat m33, pfloat m34,
+		pfloat m41, pfloat m42, pfloat m43, pfloat m44,
+		pfloat delta
+	)
+	{
+		if (AreEqual (m11, actual.M11, delta, out var d11) &
+			AreEqual (m21, actual.M21, delta, out var d21) &
+			AreEqual (m31, actual.M31, delta, out var d31) &
+			AreEqual (m41, actual.M41, delta, out var d41) &
+			AreEqual (m12, actual.M12, delta, out var d12) &
+			AreEqual (m22, actual.M22, delta, out var d22) &
+			AreEqual (m32, actual.M32, delta, out var d32) &
+			AreEqual (m42, actual.M42, delta, out var d42) &
+			AreEqual (m13, actual.M13, delta, out var d13) &
+			AreEqual (m23, actual.M23, delta, out var d23) &
+			AreEqual (m33, actual.M33, delta, out var d33) &
+			AreEqual (m43, actual.M43, delta, out var d43) &
+			AreEqual (m14, actual.M14, delta, out var d14) &
+			AreEqual (m24, actual.M24, delta, out var d24) &
+			AreEqual (m34, actual.M34, delta, out var d34) &
+			AreEqual (m44, actual.M44, delta, out var d44))
+			return;
+
+		var actualString = actual.ToString ();
+
+#if NET
+		var row1 = $"({m11}, {m21}, {m31}, {m41})";
+		var row2 = $"({m12}, {m22}, {m32}, {m42})";
+		var row3 = $"({m13}, {m23}, {m33}, {m43})";
+		var row4 = $"({m14}, {m24}, {m34}, {m44})";
+#else
+		var row1 = $"({m11}, {m12}, {m13}, {m14})";
+		var row2 = $"({m21}, {m22}, {m23}, {m24})";
+		var row3 = $"({m31}, {m32}, {m33}, {m34})";
+		var row4 = $"({m41}, {m42}, {m43}, {m44})";
+#endif
+		var expectedString = $"{row1}\n{row2}\n{row3}\n{row4}";
+
+		var diffRow1 = $"({d11}, {d12}, {d13}, {d14})";
+		var diffRow2 = $"({d21}, {d22}, {d23}, {d24})";
+		var diffRow3 = $"({d31}, {d32}, {d33}, {d34})";
+		var diffRow4 = $"({d41}, {d42}, {d43}, {d44})";
+		var diffString = $"{diffRow1}\n{diffRow2}\n{diffRow3}\n{diffRow4}";
+
+		var msg = $"{message}\nExpected:\n{expectedString}\nActual:\n{actualString}\nDiff:\n{diffString}";
+		Assert.Fail (msg);
+	}
+#endif // HAS_SCENEKIT
+
+	static bool AreEqual (pfloat expected, pfloat actual, out string emojii)
+	{
+		return AreEqual (expected, actual, 0, out emojii);
+	}
+
+	// Use our own implementation to compare two floating point numbers with a tolerance, because
+	// the NUnit version doesn't seem to work correctly in legacy Xamarin (older NUnit version?).
+	static bool AreEqual (pfloat expected, pfloat actual, pfloat tolerance, out string emojii)
+	{
+		bool rv;
+
+		if (pfloat.IsNaN (expected) && pfloat.IsNaN (actual)) {
+			rv = true;
+		} else if (pfloat.IsInfinity (expected) || pfloat.IsNaN (expected) || pfloat.IsNaN (actual)) {
+			// Handle infinity specially since subtracting two infinite values gives 
+			// NaN and the following test fails. mono also needs NaN to be handled
+			// specially although ms.net could use either method. Also, handle
+			// situation where no tolerance is used.
+			rv = expected.Equals (actual);
+		} else {
+			rv = Math.Abs (expected - actual) <= tolerance;
+		}
+
+		emojii = rv ? "✅" : "❌";
+
+		return rv;
+	}
+
+	public unsafe static void AreEqual (byte* expected, byte* actual, int length, string message)
+	{
+		// Check if the byte arrays are identical
+		var equal = true;
+		for (var i = 0; i < length; i++) {
+			var e = expected [i];
+			var a = actual [i];
+			equal &= e == a;
+		}
+		if (equal)
+			return;
+		// They're not. Create the assertion message and assert.
+		var e_sb = new StringBuilder ();
+		var a_sb = new StringBuilder ();
+		var d_sb = new StringBuilder ();
+		for (var i = 0; i < length; i++) {
+			var e = expected [i];
+			var a = actual [i];
+			e_sb.Append ($"0x{e:X2} ");
+			a_sb.Append ($"0x{a:X2} ");
+			if (e == a) {
+				d_sb.Append ("     ");
+			} else {
+				d_sb.Append ("^^^^ ");
+			}
+		}
+		Assert.Fail ($"{message}\nExpected: {e_sb}\nActual:   {a_sb}\n          {d_sb}");
+	}
 }

tests/monotouch-test/PassKit/PKPassTest.cs

@@ -0,0 +1,24 @@
+#if !__TVOS__ && !MONOMAC
+
+using System;
+using Foundation;
+using UIKit;
+using PassKit;
+using NUnit.Framework;
+
+namespace MonoTouchFixtures.PassKit {
+
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class PKPassTest {
+
+		[Test]
+		public void GetLocalizedValueNull ()
+		{
+			using var pass = new PKPass ();
+			Assert.IsNull (pass.GetLocalizedValue (new NSString ()), "'PKPass.GetLocalizedValue' is not returning a null value");
+		}
+	}
+}
+
+#endif

tests/monotouch-test/PassKit/PKPaymentRequestTest.cs

@@ -64,6 +64,28 @@ namespace MonoTouchFixtures.PassKit {
 				}
 			}
 		}
+
+		[Test]
+		public void CheckDefaultNulls ()
+		{
+			using var pr = new PKPaymentRequest ();
+			Assert.IsNull (pr.CountryCode, "'PKPaymentRequest.CountryCode' is not returning null by default.");
+			Assert.IsNull (pr.CurrencyCode, "'PKPaymentRequest.CurrencyCode' is not returning null by default.");
+			Assert.IsNull (pr.MerchantIdentifier, "'PKPaymentRequest.MerchantIdentifier' is not returning null by default.");
+			Assert.IsNull (pr.PaymentSummaryItems, "'PKPaymentRequest.PaymentSummaryItems' is not returning null by default.");
+			Assert.IsNull (pr.SupportedNetworks, "'PKPaymentRequest.SupportedNetworks' is not returning null by default.");
+
+			Assert.DoesNotThrow (delegate { pr.CountryCode = null; },
+				"'PKPaymentRequest.CountryCode' cannot be set to null.");
+			Assert.DoesNotThrow (delegate { pr.CurrencyCode = null; },
+				"'PKPaymentRequest.CurrencyCode' cannot be set to null.");
+			Assert.DoesNotThrow (delegate { pr.MerchantIdentifier = null; },
+				"'PKPaymentRequest.MerchantIdentifier' cannot be set to null.");
+			Assert.DoesNotThrow (delegate { pr.PaymentSummaryItems = null; },
+				"'PKPaymentRequest.PaymentSummaryItems' cannot be set to null.");
+			Assert.DoesNotThrow (delegate { pr.SupportedNetworks = null; },
+				"'PKPaymentRequest.SupportedNetworks' cannot be set to null.");
+		}
 	}
 }
 

tests/monotouch-test/PassKit/PKPaymentSummaryItemTest.cs

@@ -0,0 +1,30 @@
+#if !__TVOS__ && !MONOMAC
+
+using System;
+using Foundation;
+using UIKit;
+using PassKit;
+using NUnit.Framework;
+
+namespace MonoTouchFixtures.PassKit {
+
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class PKPaymentSummaryItemTest {
+
+		[Test]
+		public void CheckDefaultNulls ()
+		{
+			using var ps = new PKPaymentSummaryItem ();
+			Assert.IsNull (ps.Amount, "'PKPaymentSummaryItem.Amount' is not returning null by default.");
+			Assert.IsNull (ps.Label, "'PKPaymentSummaryItem.Label' is not returning null by default.");
+
+			Assert.DoesNotThrow (delegate { ps.Amount = null; },
+				"'PKPaymentSummaryItem.Amount' cannot be set to null.");
+			Assert.DoesNotThrow (delegate { ps.Label = null; },
+				"'PKPaymentSummaryItem.Label' cannot be set to null.");
+		}
+	}
+}
+
+#endif

tests/monotouch-test/SceneKit/SCNVector3Test.cs

@@ -0,0 +1,247 @@
+//
+// Unit tests for SCNMatrix4
+//
+// Authors:
+//	Sebastien Pouliot <sebastien@xamarin.com>
+//
+// Copyright 2014 Xamarin Inc. All rights reserved.
+//
+
+#if HAS_SCENEKIT
+
+#nullable enable
+
+using System;
+using Foundation;
+using SceneKit;
+
+using NUnit.Framework;
+
+#if __MACOS__
+#if NET
+using pfloat = System.Runtime.InteropServices.NFloat;
+#else
+using pfloat = System.nfloat;
+#endif
+#else
+using pfloat = System.Single;
+#endif
+
+namespace MonoTouchFixtures.SceneKit {
+
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class SCNVector3Test
+	{
+		static pfloat delta = (pfloat) 0.000001;
+
+		[Test]
+		public void TransformVector()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			var transformed = SCNVector3.TransformVector (pos, matrix);
+			Asserts.AreEqual (new SCNVector3 (740, 1340, 1940), transformed, "Transformed");
+		}
+
+		[Test]
+		public void TransformVector_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			SCNVector3.TransformVector (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector3 (740, 1340, 1940), transformed, "Transformed");
+		}
+
+		[Test]
+		public void TransformNormal ()
+		{
+			var matrix = new SCNMatrix4 (
+				11,  12,  13,  14,
+				21, -22,  23,  24,
+				31,  32,  33,  34,
+				41,  42,  43, -44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			pos.Normalize ();
+			var transformed = SCNVector3.TransformNormal (pos, matrix);
+			Asserts.AreEqual (new SCNVector3 ((pfloat) 0.406966, 0, (pfloat) (-0.151853)), transformed, delta, "Transformed");
+		}
+
+		[Test]
+		public void TransformNormal_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11,  12,  13,  14,
+				21, -22,  23,  24,
+				31,  32,  33,  34,
+				41,  42,  43, -44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			pos.Normalize ();
+			SCNVector3.TransformNormal (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector3 ((pfloat) 0.406966, 0, (pfloat) (-0.151853)), transformed, delta, "Transformed");
+		}
+
+		[Test]
+		public void TransformNormalInverse ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			pos.Normalize ();
+			var transformed = SCNVector3.TransformNormalInverse (pos, matrix);
+			Asserts.AreEqual (new SCNVector3 ((pfloat) 39.0201413, (pfloat) 40.62370877, (pfloat) 42.2272762), transformed, delta, "Transformed");
+		}
+
+		[Test]
+		public void TransformNormalInverse_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			pos.Normalize ();
+			SCNVector3.TransformNormalInverse (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector3 ((pfloat) 39.0201413, (pfloat) 40.62370877, (pfloat) 42.2272762), transformed, delta, "Transformed");
+		}
+
+		[Test]
+		public void TransformPosition ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			var transformed = SCNVector3.TransformPosition (pos, matrix);
+			Asserts.AreEqual (new SCNVector3 (754, 1364, 1974), transformed, "Transformed");
+		}
+
+		[Test]
+		public void TransformPosition_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			SCNVector3.TransformPosition (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector3 (754, 1364, 1974), transformed, "Transformed");
+		}
+
+		[Test]
+		public void Transform ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			var transformed = SCNVector3.Transform (pos, matrix);
+			Asserts.AreEqual (new SCNVector4 (754, 1364, 1974, 2584), transformed, "Transformed");
+		}
+
+		[Test]
+		public void Transform_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			SCNVector3.Transform (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector4 (754, 1364, 1974, 2584), transformed, "Transformed");
+		}
+
+		[Test]
+		public void TransformPerspective ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			var transformed = SCNVector3.TransformPerspective (pos, matrix);
+			Asserts.AreEqual (new SCNVector3 ((pfloat) 0.291795, (pfloat) 0.5278637, (pfloat) 0.76393188), transformed, delta, "Transformed");
+		}
+
+		[Test]
+		public void TransformPerspective_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector3 (10, 20, 30);
+			SCNVector3.TransformPerspective (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector3 ((pfloat) 0.291795, (pfloat) 0.5278637, (pfloat) 0.76393188), transformed, delta, "Transformed");
+		}
+	}
+}
+#endif // HAS_SCENEKIT

tests/monotouch-test/SceneKit/SCNVector4Test.cs

@@ -0,0 +1,73 @@
+//
+// Unit tests for SCNMatrix4
+//
+// Authors:
+//	Sebastien Pouliot <sebastien@xamarin.com>
+//
+// Copyright 2014 Xamarin Inc. All rights reserved.
+//
+
+#if HAS_SCENEKIT
+
+#nullable enable
+
+using System;
+using Foundation;
+using SceneKit;
+
+using NUnit.Framework;
+
+#if __MACOS__
+#if NET
+using pfloat = System.Runtime.InteropServices.NFloat;
+#else
+using pfloat = System.nfloat;
+#endif
+#else
+using pfloat = System.Single;
+#endif
+
+namespace MonoTouchFixtures.SceneKit {
+
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class SCNVector4Test
+	{
+		[Test]
+		public void Transform ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector4 (10, 20, 30, 40);
+			var transformed = SCNVector4.Transform (pos, matrix);
+			Asserts.AreEqual (new SCNVector4 (1300, 2300, 3300, 4300), transformed, "Transformed");
+		}
+
+		[Test]
+		public void Transform_out ()
+		{
+			var matrix = new SCNMatrix4 (
+				11, 12, 13, 14,
+				21, 22, 23, 24,
+				31, 32, 33, 34,
+				41, 42, 43, 44);
+#if !NET
+			matrix.Transpose ();
+#endif
+
+			var pos = new SCNVector4 (10, 20, 30, 40);
+			SCNVector4.Transform (ref pos, ref matrix, out var transformed);
+			Asserts.AreEqual (new SCNVector4 (1300, 2300, 3300, 4300), transformed, "Transformed");
+		}
+
+	}
+}
+
+#endif // HAS_SCENEKIT

tests/monotouch-test/monotouch-test.csproj

@@ -223,6 +223,8 @@
     <Compile Include="..\..\tools\common\ApplePlatform.cs">
       <Link>ApplePlatform.cs</Link>
     </Compile>
+    <Compile Include="SceneKit\SCNVector3Test.cs" />
+    <Compile Include="SceneKit\SCNVector4Test.cs" />
   </ItemGroup>
   <Import Project="$(RootTestsDirectory)\nunit.framework.targets" />
   <Import Project="$(MSBuildExtensionsPath)\Xamarin\iOS\Xamarin.iOS.CSharp.targets" />

tests/msbuild/Xamarin.MacDev.Tasks.Tests/TaskTests/DetectSdkLocationsTaskTests.cs

@@ -3,7 +3,9 @@ using System.IO;
 
 using NUnit.Framework;
 
-namespace Xamarin.iOS.Tasks
+using Xamarin.iOS.Tasks;
+
+namespace Xamarin.MacDev.Tasks
 {
 	[TestFixture]
 	public class DetectSdkLocationsTaskTests : TestBase

tests/msbuild/Xamarin.MacDev.Tasks.Tests/TaskTests/ToolTasksBinPathTest.cs

@@ -55,7 +55,7 @@ namespace Xamarin.MacDev.Tasks {
 				RedirectStandardOutput = true,
 				RedirectStandardError = true,
 			};
-			psi.EnvironmentVariables.Add ("DEVELOPER_DIR", Configuration.xcode_root);
+			psi.EnvironmentVariables ["DEVELOPER_DIR"] =Configuration.xcode_root;
 			psi.EnvironmentVariables.Remove ("XCODE_DEVELOPER_DIR_PATH"); // VSfM sets XCODE_DEVELOPER_DIR_PATH, which confuses the command-line tools if it doesn't match xcode-select, so just unset it.
 			var proc = Process.Start (psi);
 

tests/packaged-macos-tests.mk

@@ -6,7 +6,6 @@ include $(TOP)/Make.config
 
 export TargetFrameworkFallbackSearchPaths:=$(MAC_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild-frameworks
 export MSBuildExtensionsPathFallbackPathsOverride:=$(MAC_DESTDIR)/Library/Frameworks/Mono.framework/External/xbuild
-export MD_APPLE_SDK_ROOT=$(abspath $(XCODE_DEVELOPER_ROOT)/../..)
 
 ifeq ($(shell uname -a),"arm64")
 IS_ARM64=1

tests/test-libraries/libtest.h

@@ -8,6 +8,8 @@
 #import <ModelIO/ModelIO.h>
 #endif
 
+#import <SceneKit/SceneKit.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -29,6 +31,16 @@ void x_mdltransform_create_global_transform (MDLObject *object, NSTimeInterval t
 void x_mdltransform_get_rotation_matrix (MDLTransform *self, NSTimeInterval time, float* r0c0, float* r0c1, float* r0c2, float* r0c3, float* r1c0, float* r1c1, float* r1c2, float* r1c3, float* r2c0, float* r2c1, float* r2c2, float* r2c3, float* r3c0, float* r3c1, float* r3c2, float* r3c3);
 #endif
 
+#if TARGET_OS_OSX
+#define pfloat CGFloat
+#else
+#define pfloat float
+#endif
+
+SCNMatrix4 x_SCNMatrix4MakeTranslation (pfloat tx, pfloat ty, pfloat tz);
+SCNMatrix4 x_SCNMatrix4MakeScale (pfloat tx, pfloat ty, pfloat tz);
+SCNMatrix4 x_SCNMatrix4Translate (SCNMatrix4 m, pfloat tx, pfloat ty, pfloat tz);
+
 /*
  * Various structs used in ObjCRegistrarTest
  */

tests/test-libraries/libtest.m

@@ -250,6 +250,24 @@ x_mdltransform_get_rotation_matrix (MDLTransform *self, NSTimeInterval time,
 }
 #endif // !TARGET_OS_WATCH
 
+SCNMatrix4
+x_SCNMatrix4MakeTranslation (pfloat tx, pfloat ty, pfloat tz)
+{
+	return SCNMatrix4MakeTranslation (tx, ty, tz);
+}
+
+SCNMatrix4
+x_SCNMatrix4MakeScale (pfloat tx, pfloat ty, pfloat tz)
+{
+	return SCNMatrix4MakeScale (tx, ty, tz);
+}
+
+SCNMatrix4
+x_SCNMatrix4Translate (SCNMatrix4 m, pfloat tx, pfloat ty, pfloat tz)
+{
+	return SCNMatrix4Translate (m, tx, ty, tz);
+}
+
 @interface UltimateMachine : NSObject {
 
 }

tests/test-libraries/rename.h

@@ -68,6 +68,9 @@
 	#define x_get_matrix_float3x3 object_x_get_matrix_float3x3
 	#define x_get_matrix_float2x2 object_x_get_matrix_float2x2
 	#define x_call_block          object_x_call_block
+	#define x_SCNMatrix4MakeTranslation object_x_SCNMatrix4MakeTranslation
+	#define x_SCNMatrix4MakeScale       object_x_SCNMatrix4MakeScale
+	#define x_SCNMatrix4Translate       object_x_SCNMatrix4Translate
 #elif PREFIX == 2
 	#define theUltimateAnswer ar_theUltimateAnswer
 	#define useZLib           ar_useZLib
@@ -137,6 +140,9 @@
 	#define x_get_matrix_float3x3 ar_x_get_matrix_float3x3
 	#define x_get_matrix_float2x2 ar_x_get_matrix_float2x2
 	#define x_call_block          ar_x_call_block
+	#define x_SCNMatrix4MakeTranslation ar_x_SCNMatrix4MakeTranslation
+	#define x_SCNMatrix4MakeScale       ar_x_SCNMatrix4MakeScale
+	#define x_SCNMatrix4Translate       ar_x_SCNMatrix4Translate
 #else
 // keep original names
 #endif