[Xaml[C]] cast to BindingBase before SetBinding() (#709)

Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs

@@ -724,7 +724,7 @@ namespace Xamarin.Forms.Build.Tasks
 			if (CanAdd(parent, localName, valueNode, context))
 				return Add(parent, localName, valueNode, iXmlLineInfo, context);
 
-			throw new XamlParseException($"No property, bindable property, or event found for '{localName}'", iXmlLineInfo);
+			throw new XamlParseException($"No property, bindable property, or event found for '{localName}', or mismatching type between value and property.", iXmlLineInfo);
 		}
 
 		static FieldReference GetBindablePropertyReference(VariableDefinition parent, string namespaceURI, ref string localName, out bool attached, ILContext context, IXmlLineInfo iXmlLineInfo)
@@ -838,6 +838,10 @@ namespace Xamarin.Forms.Build.Tasks
 			VariableDefinition varValue;
 			if (!context.Variables.TryGetValue(valueNode as IElementNode, out varValue))
 				return false;
+			var implicitOperator = varValue.VariableType.GetImplicitOperatorTo(module.Import(typeof(BindingBase)), module);
+			if (implicitOperator != null)
+				return true;
+
 			return varValue.VariableType.InheritsFromOrImplements(module.Import(typeof(BindingBase)));
 		}
 
@@ -845,6 +849,7 @@ namespace Xamarin.Forms.Build.Tasks
 		{
 			var module = context.Body.Method.Module;
 			var varValue = context.Variables [elementNode];
+			var implicitOperator = varValue.VariableType.GetImplicitOperatorTo(module.Import(typeof(BindingBase)), module);
 
 			//TODO: check if parent is a BP
 			var setBinding = typeof(BindableObject).GetMethod("SetBinding", new [] { typeof(BindableProperty), typeof(BindingBase) });
@@ -852,6 +857,9 @@ namespace Xamarin.Forms.Build.Tasks
 			yield return Instruction.Create(OpCodes.Ldloc, parent);
 			yield return Instruction.Create(OpCodes.Ldsfld, bpRef);
 			yield return Instruction.Create(OpCodes.Ldloc, varValue);
+			if (implicitOperator != null) 
+//				IL_000f:  call !0 class [Xamarin.Forms.Core]Xamarin.Forms.OnPlatform`1<BindingBase>::op_Implicit(class [Xamarin.Forms.Core]Xamarin.Forms.OnPlatform`1<!0>)
+				yield return Instruction.Create(OpCodes.Call, module.Import(implicitOperator));
 			yield return Instruction.Create(OpCodes.Callvirt, module.Import(setBinding));
 		}
 

Xamarin.Forms.Xaml.UnitTests/Issues/Bz44213.xaml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="Xamarin.Forms.Xaml.UnitTests.Bz44213">
+	<Label x:Name="label">
+		<Label.Text>
+			<OnPlatform x:TypeArguments="BindingBase" Android="{Binding Bar}">
+				<OnPlatform.iOS>
+					<Binding Path="Foo"/>
+				</OnPlatform.iOS>
+			</OnPlatform>
+		</Label.Text>
+	</Label>
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Bz44213.xaml.cs

@@ -0,0 +1,48 @@
+using NUnit.Framework;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	public partial class Bz44213 : ContentPage
+	{
+		public Bz44213()
+		{
+			InitializeComponent();
+		}
+
+		public Bz44213(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		[TestFixture]
+		class Tests
+		{
+			[SetUp]
+			public void Setup()
+			{
+				Device.PlatformServices = new MockPlatformServices();
+			}
+
+			[TearDown]
+			public void TearDown()
+			{
+				Device.PlatformServices = null;
+			}
+
+			[TestCase(true)]
+			[TestCase(false)]
+			public void BindingInOnPlatform(bool useCompiledXaml)
+			{
+				((MockPlatformServices)Device.PlatformServices).RuntimePlatform = Device.iOS;
+				var p = new Bz44213(useCompiledXaml);
+				p.BindingContext = new { Foo = "Foo", Bar = "Bar" };
+				Assert.AreEqual("Foo", p.label.Text);
+				((MockPlatformServices)Device.PlatformServices).RuntimePlatform = Device.Android;
+				p = new Bz44213(useCompiledXaml);
+				p.BindingContext = new { Foo = "Foo", Bar = "Bar" };
+				Assert.AreEqual("Bar", p.label.Text);
+			}
+		}
+	}
+}

Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj

@@ -424,6 +424,9 @@
     <Compile Include="Issues\Bz43733.xaml.cs">
       <DependentUpon>Bz43733.xaml</DependentUpon>
     </Compile>
+    <Compile Include="Issues\Bz44213.xaml.cs">
+      <DependentUpon>Bz44213.xaml</DependentUpon>
+    </Compile>
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="..\.nuspec\Xamarin.Forms.Debug.targets" />
@@ -769,6 +772,9 @@
     <EmbeddedResource Include="Issues\Bz43733.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="Issues\Bz44213.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />

Xamarin.Forms.Xaml/ApplyPropertiesVisitor.cs

@@ -361,7 +361,7 @@ namespace Xamarin.Forms.Xaml
 			exception = null;
 
 			var elementType = element.GetType();
-			var binding = value as BindingBase;
+			var binding = value.ConvertTo(typeof(BindingBase),pinfoRetriever:null,serviceProvider:null) as BindingBase;
 			var bindable = element as BindableObject;
 			var nativeBindingService = DependencyService.Get<INativeBindingService>();