[Android] Don't crash if Control is accessed in Effect OnDetached when Page is Disposed. (#773)

* Add repro for 51505

* [Android] Don't dispose of EffectControlProvider

* Oops

1 files changed, 62 insertions, 30 deletions

diff --git a/Xamarin.Forms.ControlGallery.WindowsUniversal/MainPage.xaml.cs b/Xamarin.Forms.ControlGallery.WindowsUniversal/MainPage.xaml.cs
index 744e4d19..5f4ea08d 100644
--- a/Xamarin.Forms.ControlGallery.WindowsUniversal/MainPage.xaml.cs
+++ b/Xamarin.Forms.ControlGallery.WindowsUniversal/MainPage.xaml.cs
@@ -8,34 +8,59 @@ using Windows.UI.ViewManagement;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
 using Windows.UI.Xaml.Media;
+using Xamarin.Forms;
+using Xamarin.Forms.ControlGallery.WindowsUniversal;
 using Xamarin.Forms.Controls;
 using Xamarin.Forms.Platform.UWP;
 
+[assembly: ExportEffect(typeof(BorderEffect), "BorderEffect")]
 namespace Xamarin.Forms.ControlGallery.WindowsUniversal
 {
+	public class BorderEffect : PlatformEffect
+	{
+		protected override void OnAttached()
+		{
+			var control = Control as Control;
+			if (control == null)
+				return;
+
+			control.Background = new SolidColorBrush(Windows.UI.Colors.Aqua);
+		}
+
+		protected override void OnDetached()
+		{
+			var control = Control as Control;
+			if (control == null)
+				return;
+
+			control.Background = new SolidColorBrush(Windows.UI.Colors.Beige);
+		}
+	}
+
 	/// <summary>
 	/// An empty page that can be used on its own or navigated to within a Frame.
 	/// </summary>
 	public sealed partial class MainPage
-    {
-        public MainPage()
-        {
-            InitializeComponent();
+	{
+		public MainPage()
+		{
+			InitializeComponent();
 
-			var app = new Controls.App ();
+			var app = new Controls.App();
 
 			// When the native control gallery loads up, it'll let us know so we can add the nested native controls
 			MessagingCenter.Subscribe<NestedNativeControlGalleryPage>(this, NestedNativeControlGalleryPage.ReadyForNativeControlsMessage, AddNativeControls);
-					
+
 			// When the native binding gallery loads up, it'll let us know so we can set up the native bindings
-			MessagingCenter.Subscribe<NativeBindingGalleryPage >(this, NativeBindingGalleryPage.ReadyForNativeBindingsMessage, AddNativeBindings);
+			MessagingCenter.Subscribe<NativeBindingGalleryPage>(this, NativeBindingGalleryPage.ReadyForNativeBindingsMessage, AddNativeBindings);
 
-			LoadApplication (app);
-        }
+			LoadApplication(app);
+		}
 
-		void AddNativeControls (NestedNativeControlGalleryPage page)
+		void AddNativeControls(NestedNativeControlGalleryPage page)
 		{
-			if (page.NativeControlsAdded) {
+			if (page.NativeControlsAdded)
+			{
 				return;
 			}
 
@@ -43,54 +68,59 @@ namespace Xamarin.Forms.ControlGallery.WindowsUniversal
 
 			// Create and add a native TextBlock
 			var originalText = "I am a native TextBlock";
-			var textBlock = new TextBlock {
+			var textBlock = new TextBlock
+			{
 				Text = originalText,
 				FontSize = 14,
-				FontFamily = new FontFamily ("HelveticaNeue")
+				FontFamily = new FontFamily("HelveticaNeue")
 			};
 
-			sl?.Children.Add (textBlock);
+			sl?.Children.Add(textBlock);
 
 			// Create and add a native Button 
 			var button = new Windows.UI.Xaml.Controls.Button { Content = "Toggle Font Size", Height = 80 };
 			button.Click += (sender, args) => { textBlock.FontSize = textBlock.FontSize == 14 ? 24 : 14; };
 
-			sl?.Children.Add (button.ToView ());
+			sl?.Children.Add(button.ToView());
 
 			// Create a control which we know doesn't behave correctly with regard to measurement
-			var difficultControl = new BrokenNativeControl {
+			var difficultControl = new BrokenNativeControl
+			{
 				Text = "Not Sized/Arranged Properly"
 			};
 
-			var difficultControl2 = new BrokenNativeControl {
+			var difficultControl2 = new BrokenNativeControl
+			{
 				Text = "Fixed"
 			};
 
 			// Add the misbehaving controls, one with a custom delegate for ArrangeOverrideDelegate
-			sl?.Children.Add (difficultControl);
-			sl?.Children.Add (difficultControl2,
-				arrangeOverrideDelegate: (renderer, finalSize) => {
-					if (finalSize.Width <= 0 || double.IsInfinity (finalSize.Width)) {
+			sl?.Children.Add(difficultControl);
+			sl?.Children.Add(difficultControl2,
+				arrangeOverrideDelegate: (renderer, finalSize) =>
+				{
+					if (finalSize.Width <= 0 || double.IsInfinity(finalSize.Width))
+					{
 						return null;
 					}
 
 					FrameworkElement frameworkElement = renderer.Control;
 
-					frameworkElement.Measure (finalSize);
+					frameworkElement.Measure(finalSize);
 
 					// The broken control always tries to size itself to the screen width
 					// So figure that out and we'll know how far off it's laying itself out
-					Rect bounds = ApplicationView.GetForCurrentView ().VisibleBounds;
-					double scaleFactor = DisplayInformation.GetForCurrentView ().RawPixelsPerViewPixel;
-					var screenWidth = new Size (bounds.Width * scaleFactor, bounds.Height * scaleFactor);
-					
+					Rect bounds = ApplicationView.GetForCurrentView().VisibleBounds;
+					double scaleFactor = DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
+					var screenWidth = new Size(bounds.Width * scaleFactor, bounds.Height * scaleFactor);
+
 					// We can re-center it by offsetting it during the Arrange call
 					double diff = Math.Abs(screenWidth.Width - finalSize.Width) / -2;
-					frameworkElement.Arrange (new Rect (diff, 0, finalSize.Width - diff, finalSize.Height));
+					frameworkElement.Arrange(new Rect(diff, 0, finalSize.Width - diff, finalSize.Height));
 
 					// Arranging the control to the left will make it show up past the edge of the stack layout
 					// We can fix that by clipping it manually
-					var clip = new RectangleGeometry { Rect = new Rect (-diff, 0, finalSize.Width, finalSize.Height) };
+					var clip = new RectangleGeometry { Rect = new Rect(-diff, 0, finalSize.Width, finalSize.Height) };
 					frameworkElement.Clip = clip;
 
 					return finalSize;
@@ -107,12 +137,14 @@ namespace Xamarin.Forms.ControlGallery.WindowsUniversal
 
 			StackLayout sl = page.Layout;
 
-			var txbLabel = new TextBlock {
+			var txbLabel = new TextBlock
+			{
 				FontSize = 14,
 				FontFamily = new FontFamily("HelveticaNeue")
 			};
 
-			var txbBox = new TextBox {
+			var txbBox = new TextBox
+			{
 				FontSize = 14,
 				FontFamily = new FontFamily("HelveticaNeue")
 			};