Implemented MediaElement ObjectDisposedException fix (#1870)

Implemented fix

Author: anvuks

src/CommunityToolkit/Xamarin.CommunityToolkit/Views/MediaElement/Android/FormsVideoView.android.cs

@@ -52,10 +52,14 @@ protected void ExtractMetadata(MediaMetadataRetriever retriever)
 
 		public override async void SetVideoURI(global::Android.Net.Uri? uri, IDictionary<string, string>? headers)
 		{
+			base.SetVideoURI(uri, headers);
+
+			// this instance could get disposed during awaiting, so a call to the base method (AFTER awaiting)
+			// would throw ObjectDisposedException and be impossible to catch due to async void
 			if (uri != null)
+			{
 				await SetMetadata(uri, headers);
-
-			base.SetVideoURI(uri, headers);
+			}
 		}
 
 		protected async Task SetMetadata(global::Android.Net.Uri uri, IDictionary<string, string>? headers)

src/CommunityToolkit/Xamarin.CommunityToolkit/Views/MediaElement/Android/MediaElementRenderer.android.cs

@@ -21,7 +21,7 @@ public class MediaElementRenderer : FrameLayout, IVisualElementRenderer, IViewRe
 		VisualElementTracker? tracker;
 		protected MediaController? controller;
 		protected MediaPlayer? mediaPlayer;
-		protected FormsVideoView view;
+		protected FormsVideoView? view;
 		bool isDisposed;
 		int? defaultLabelFor;
 
@@ -47,9 +47,14 @@ public MediaElementRenderer(Context context)
 
 		public override float Alpha
 		{
-			get => view.Alpha;
+			get => view?.Alpha ?? throw new ObjectDisposedException(typeof(FormsVideoView).FullName);
 			set
 			{
+				if (view == null)
+				{
+					throw new ObjectDisposedException(typeof(FormsVideoView).FullName);
+				}
+
 				// VideoView opens a separate Window above the current one.
 				// This is because it is based on the SurfaceView.
 				// And we cannot set alpha or perform animations with it because it is not synchronized with your other UI elements.
@@ -509,6 +514,7 @@ protected virtual void ReleaseControl()
 				view.SetOnPreparedListener(null);
 				view.SetOnCompletionListener(null);
 				view.Dispose();
+				view = null;
 			}
 
 			if (controller != null)