A few changes so that the views can detect a designer

Related to #234

source/SkiaSharp.Views/SkiaSharp.Views.Android/SKCanvasView.cs

@@ -13,6 +13,8 @@ namespace SkiaSharp.Views.Android
 		private SKImageInfo info;
 		private bool ignorePixelScaling;
 
+		private bool designMode;
+		
 		public SKCanvasView(Context context)
 			: base(context)
 		{
@@ -39,6 +41,11 @@ namespace SkiaSharp.Views.Android
 
 		private void Initialize()
 		{
+			designMode = !Extensions.IsValidEnvironment;
+
+			if (designMode)
+				return;
+
 			// create the initial info
 			info = new SKImageInfo(0, 0, SKColorType.Rgba8888, SKAlphaType.Premul);
 		}
@@ -60,6 +67,9 @@ namespace SkiaSharp.Views.Android
 		{
 			base.OnDraw(canvas);
 
+			if (designMode)
+				return;
+
 			// create the bitmap data if we need it
 			if (bitmap == null || bitmap.Width != info.Width || bitmap.Height != info.Height)
 			{
@@ -94,6 +104,9 @@ namespace SkiaSharp.Views.Android
 
 		private void UpdateCanvasSize(int w, int h)
 		{
+			if (designMode)
+				return;
+
 			if (IgnorePixelScaling)
 			{
 				var scale = Resources.DisplayMetrics.Density;

source/SkiaSharp.Views/SkiaSharp.Views.AppleiOS/SKCanvasView.cs

@@ -49,17 +49,20 @@ namespace SkiaSharp.Views.iOS
 		// created via designer
 		public override void AwakeFromNib()
 		{
-			designMode = ((IComponent)this).Site?.DesignMode == true;
-
 			Initialize();
 		}
 
 		private void Initialize()
 		{
+			designMode = ((IComponent)this).Site?.DesignMode == true || !Extensions.IsValidEnvironment;
+
+			if (designMode)
+				return;
+
 			drawable = new SKDrawable();
 		}
 
-		public SKSize CanvasSize => drawable.Info.Size;
+		public SKSize CanvasSize => drawable?.Info.Size ?? SKSize.Empty;
 
 		public bool IgnorePixelScaling
 		{
@@ -75,7 +78,7 @@ namespace SkiaSharp.Views.iOS
 		{
 			base.Draw(rect);
 
-			if (designMode)
+			if (designMode || drawable == null)
 				return;
 
 			var ctx = UIGraphics.GetCurrentContext();
@@ -109,7 +112,7 @@ namespace SkiaSharp.Views.iOS
 		{
 			base.Dispose(disposing);
 
-			drawable.Dispose();
+			drawable?.Dispose();
 		}
 	}
 }

source/SkiaSharp.Views/SkiaSharp.Views.AppleiOS/SKGLView.cs

@@ -50,13 +50,16 @@ namespace SkiaSharp.Views.iOS
 		// created via designer
 		public override void AwakeFromNib()
 		{
-			designMode = ((IComponent)this).Site?.DesignMode == true;
-
 			Initialize();
 		}
 
 		private void Initialize()
 		{
+			designMode = ((IComponent)this).Site?.DesignMode == true || !Extensions.IsValidEnvironment;
+
+			if (designMode)
+				return;
+
 			// create the GL context
 			Context = new EAGLContext(EAGLRenderingAPI.OpenGLES2);
 			DrawableColorFormat = GLKViewDrawableColorFormat.RGBA8888;

source/SkiaSharp.Views/SkiaSharp.Views.Shared/Extensions.cs

@@ -1,4 +1,5 @@
-#if __ANDROID__
+using System;
+#if __ANDROID__
 namespace SkiaSharp.Views.Android
 #elif __TVOS__
 namespace SkiaSharp.Views.tvOS
@@ -14,6 +15,26 @@ namespace SkiaSharp.Views.Mac
 {
 	public static class Extensions
 	{
+		private static readonly Lazy<bool> isValidEnvironment = new Lazy<bool>(() =>
+		{
+			try
+			{
+				// test an operation that requires the native library
+				SKPMColor.PreMultiply(SKColors.Black);
+				return true;
+			}
+			catch (DllNotFoundException)
+			{
+				// If we can't load the native library,
+				// we may be in some designer.
+				// We can make this assumption since any other member will fail
+				// at some point in the draw operation.
+				return false;
+			}
+		});
+
+		internal static bool IsValidEnvironment => isValidEnvironment.Value;
+
 #if !WINDOWS_UWP
 		// System.Drawing.Point*