Better error handling for image loading errors on iOS/Android (#849)

* First run at removing async void image update methods

Consistent error logging and IsLoading on Android,iOS,UWP

Move error logging into image handlers for better messages

Add demo of custom ImageRenderer error handling

Update docs

Make the test smaller so the results don't get pushed offscreen

Fix namespace error

* Update error handling for fast image renderer

* Update 37625 test to use image we control

* Add java disposed check to avoid ObjectDisposedException in async operations

* Add disposed checks to legacy renderer; null check element before SetIsLoading

* Check disposed on GetDesiredSize for fast renderer
Use local disposed member where possible for disposed check

* Check for disposal after async handlers in iOS

* Add disposal checks after async methods in Windows

* Reset linker settings on project; reduce redundant casts in ImageViewExtensions

4 files changed, 74 insertions, 15 deletions

diff --git a/Xamarin.Forms.Platform.Android/Renderers/FileImageSourceHandler.cs b/Xamarin.Forms.Platform.Android/Renderers/FileImageSourceHandler.cs
index 93124fef..95d66fb7 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/FileImageSourceHandler.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/FileImageSourceHandler.cs
@@ -3,6 +3,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Android.Content;
 using Android.Graphics;
+using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms.Platform.Android
 {
@@ -17,10 +18,18 @@ namespace Xamarin.Forms.Platform.Android
 		public async Task<Bitmap> LoadImageAsync(ImageSource imagesource, Context context, CancellationToken cancelationToken = default(CancellationToken))
 		{
 			string file = ((FileImageSource)imagesource).File;
+			Bitmap bitmap;
 			if (File.Exists (file))
-				return !DecodeSynchronously ? (await BitmapFactory.DecodeFileAsync (file).ConfigureAwait (false)) : BitmapFactory.DecodeFile (file);
+				bitmap = !DecodeSynchronously ? (await BitmapFactory.DecodeFileAsync (file).ConfigureAwait (false)) : BitmapFactory.DecodeFile (file);
 			else
-				return !DecodeSynchronously ? (await context.Resources.GetBitmapAsync (file).ConfigureAwait (false)) : context.Resources.GetBitmap (file);
+				bitmap = !DecodeSynchronously ? (await context.Resources.GetBitmapAsync (file).ConfigureAwait (false)) : context.Resources.GetBitmap (file);
+
+			if (bitmap == null)
+			{
+				Log.Warning(nameof(FileImageSourceHandler), "Could not find image or image file was invalid: {0}", imagesource);
+			}
+
+			return bitmap;
 		}
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Platform.Android/Renderers/ImageLoaderSourceHandler.cs b/Xamarin.Forms.Platform.Android/Renderers/ImageLoaderSourceHandler.cs
index 8d0ae3d9..b22ca485 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/ImageLoaderSourceHandler.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/ImageLoaderSourceHandler.cs
@@ -3,6 +3,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Android.Content;
 using Android.Graphics;
+using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms.Platform.Android
 {
@@ -11,12 +12,19 @@ namespace Xamarin.Forms.Platform.Android
 		public async Task<Bitmap> LoadImageAsync(ImageSource imagesource, Context context, CancellationToken cancelationToken = default(CancellationToken))
 		{
 			var imageLoader = imagesource as UriImageSource;
-			if (imageLoader != null && imageLoader.Uri != null)
+			Bitmap bitmap = null;
+			if (imageLoader?.Uri != null)
 			{
 				using (Stream imageStream = await imageLoader.GetStreamAsync(cancelationToken).ConfigureAwait(false))
-					return await BitmapFactory.DecodeStreamAsync(imageStream).ConfigureAwait(false);
+					bitmap =  await BitmapFactory.DecodeStreamAsync(imageStream).ConfigureAwait(false);
 			}
-			return null;
+
+			if (bitmap == null)
+			{
+				Log.Warning(nameof(ImageLoaderSourceHandler), "Could not retrieve image or image data was invalid: {0}", imageLoader);
+			}
+
+			return bitmap;
 		}
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Platform.Android/Renderers/ImageRenderer.cs b/Xamarin.Forms.Platform.Android/Renderers/ImageRenderer.cs
index 57937d89..43dac1fe 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/ImageRenderer.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/ImageRenderer.cs
@@ -1,10 +1,10 @@
 using System;
 using System.ComponentModel;
+using System.Threading.Tasks;
 using Android.Graphics;
 using Android.Views;
 using AImageView = Android.Widget.ImageView;
 using Xamarin.Forms.Internals;
-using static Xamarin.Forms.Platform.Android.ImageViewExtensions;
 
 namespace Xamarin.Forms.Platform.Android
 {
@@ -20,7 +20,6 @@ namespace Xamarin.Forms.Platform.Android
 
 		public ImageRenderer()
 		{
-            System.Diagnostics.Debug.WriteLine(">>>>> Old Image Renderer");
 			AutoPackage = false;
 		}
 
@@ -39,7 +38,7 @@ namespace Xamarin.Forms.Platform.Android
 			return new FormsImageView(Context);
 		}
 
-		protected override void OnElementChanged(ElementChangedEventArgs<Image> e)
+		protected override async void OnElementChanged(ElementChangedEventArgs<Image> e)
 		{
 			base.OnElementChanged(e);
 
@@ -50,28 +49,63 @@ namespace Xamarin.Forms.Platform.Android
 			}
 
 			_motionEventHelper.UpdateElement(e.NewElement);
-			
-			Control.UpdateBitmap(e.NewElement, e.OldElement);
+
+			await TryUpdateBitmap(e.OldElement);
 
 			UpdateAspect();
 		}
 
-		protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
+		protected override async void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
 		{
 			base.OnElementPropertyChanged(sender, e);
 
 			if (e.PropertyName == Image.SourceProperty.PropertyName)
-				Control.UpdateBitmap(Element);
+				await TryUpdateBitmap();
 			else if (e.PropertyName == Image.AspectProperty.PropertyName)
 				UpdateAspect();
 		}
 
 		void UpdateAspect()
 		{
+			if (Element == null || Control == null || Control.IsDisposed())
+			{
+				return;
+			}
+
 			AImageView.ScaleType type = Element.Aspect.ToScaleType();
 			Control.SetScaleType(type);
 		}
 
+		protected virtual async Task TryUpdateBitmap(Image previous = null)
+		{
+			// By default we'll just catch and log any exceptions thrown by UpdateBitmap so they don't bring down
+			// the application; a custom renderer can override this method and handle exceptions from
+			// UpdateBitmap differently if it wants to
+
+			try
+			{
+				await UpdateBitmap(previous);
+			}
+			catch (Exception ex)
+			{
+				Log.Warning(nameof(ImageRenderer), "Error loading image: {0}", ex);
+			}
+			finally
+			{
+				((IImageController)Element)?.SetIsLoading(false);
+			}
+		}
+
+		protected async Task UpdateBitmap(Image previous = null)
+		{
+			if (Element == null || Control == null || Control.IsDisposed())
+			{
+				return;
+			}
+
+			await Control.UpdateBitmap(Element, previous);
+		}
+
         public override bool OnTouchEvent(MotionEvent e)
         {
             if (base.OnTouchEvent(e))
diff --git a/Xamarin.Forms.Platform.Android/Renderers/StreamImagesourceHandler.cs b/Xamarin.Forms.Platform.Android/Renderers/StreamImagesourceHandler.cs
index 3128995d..a46e3abc 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/StreamImagesourceHandler.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/StreamImagesourceHandler.cs
@@ -3,6 +3,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Android.Content;
 using Android.Graphics;
+using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms.Platform.Android
 {
@@ -11,12 +12,19 @@ namespace Xamarin.Forms.Platform.Android
 		public async Task<Bitmap> LoadImageAsync(ImageSource imagesource, Context context, CancellationToken cancelationToken = default(CancellationToken))
 		{
 			var streamsource = imagesource as StreamImageSource;
-			if (streamsource != null && streamsource.Stream != null)
+			Bitmap bitmap = null;
+			if (streamsource?.Stream != null)
 			{
 				using (Stream stream = await ((IStreamImageSource)streamsource).GetStreamAsync(cancelationToken).ConfigureAwait(false))
-					return await BitmapFactory.DecodeStreamAsync(stream).ConfigureAwait(false);
+					bitmap = await BitmapFactory.DecodeStreamAsync(stream).ConfigureAwait(false);
 			}
-			return null;
+
+			if (bitmap == null)
+			{
+				Log.Warning(nameof(ImageLoaderSourceHandler), "Image data was invalid: {0}", streamsource);
+			}
+
+			return bitmap;
 		}
 	}
 }
\ No newline at end of file