Call disconnect on previous handler with Shell (#8455)

* Wire up DisconnectHandler for Shell

* - Add tests for swapping out same window/shell with new context

* - add overrides for windows/ios

* Update ShellRenderer.cs

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellFlyoutRecyclerAdapter.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Maui.Controls.Platform.Compatibility
 {
 	public class ShellFlyoutRecyclerAdapter : RecyclerView.Adapter
 	{
-		readonly IShellContext _shellContext;
+		IShellContext _shellContext;
 		List<AdapterListItem> _listItems;
 		List<List<Element>> _flyoutGroupings;
 		Action<Element> _selectedCallback;
@@ -203,15 +203,22 @@ protected override void Dispose(bool disposing)
 
 			if (disposing)
 			{
-				((IShellController)Shell).FlyoutItemsChanged -= OnFlyoutItemsChanged;
-
-				_listItems = null;
-				_selectedCallback = null;
+				Disconnect();
 			}
 
 			base.Dispose(disposing);
 		}
 
+		internal void Disconnect()
+		{
+			if (Shell is IShellController scc)
+				scc.FlyoutItemsChanged -= OnFlyoutItemsChanged;
+
+			_listItems = null;
+			_selectedCallback = null;
+			_shellContext = null;
+		}
+
 		public class AdapterListItem
 		{
 			// This ensures that we have a stable id for each element

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellFlyoutRenderer.cs

@@ -118,7 +118,7 @@ void IFlyoutBehaviorObserver.OnFlyoutBehaviorChanged(FlyoutBehavior behavior)
 		#endregion IFlyoutBehaviorObserver
 
 		const uint DefaultScrimColor = 0x99000000;
-		readonly IShellContext _shellContext;
+		IShellContext _shellContext;
 		AView _content;
 		IShellFlyoutContentRenderer _flyoutContent;
 		int _flyoutWidthDefault;
@@ -391,24 +391,41 @@ void UpdateScrim(Brush backdrop)
 			}
 		}
 
-		protected override void Dispose(bool disposing)
+		internal void Disconnect()
 		{
-			if (_disposed)
-				return;
+			ShellController?.RemoveAppearanceObserver(this);
 
-			_disposed = true;
-
-			if (disposing)
-			{
-				ShellController.RemoveAppearanceObserver(this);
+			if (Shell != null)
 				Shell.PropertyChanged -= OnShellPropertyChanged;
 
+			if (this.IsAlive())
+			{
 				this.DrawerClosed -= OnDrawerClosed;
 				this.DrawerSlide -= OnDrawerSlide;
 				this.DrawerOpened -= OnDrawerOpened;
 				this.DrawerStateChanged -= OnDrawerStateChanged;
+			}
+
+			ShellController?.RemoveFlyoutBehaviorObserver(this);
+
+			if (_flyoutContent is ShellFlyoutTemplatedContentRenderer flyoutTemplatedContentRenderer)
+			{
+				flyoutTemplatedContentRenderer.Disconnect();
+			}
+
+			_shellContext = null;
+		}
+
+		protected override void Dispose(bool disposing)
+		{
+			if (_disposed)
+				return;
+
+			_disposed = true;
 
-				((IShellController)_shellContext.Shell).RemoveFlyoutBehaviorObserver(this);
+			if (disposing)
+			{
+				Disconnect();
 
 				RemoveView(_content);
 

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellFlyoutTemplatedContentRenderer.cs

@@ -199,6 +199,17 @@ protected virtual void UpdateFlyoutContent()
 			UpdateContentPadding();
 		}
 
+
+		void DisconnectRecyclerView()
+		{
+			if (_flyoutContentView.IsAlive() &&
+				_flyoutContentView is RecyclerViewContainer rvc &&
+				rvc.GetAdapter() is ShellFlyoutRecyclerAdapter sfra)
+			{
+				sfra.Disconnect();
+			}
+		}
+
 		AView CreateFlyoutContent(ViewGroup rootView)
 		{
 			_rootView = rootView;
@@ -209,6 +220,8 @@ AView CreateFlyoutContent(ViewGroup rootView)
 				oldContentView.View = null;
 			}
 
+			DisconnectRecyclerView();
+
 			var content = ((IShellController)ShellContext.Shell).FlyoutContent;
 			if (content == null)
 			{
@@ -592,6 +605,26 @@ public void OnOffsetChanged(AppBarLayout appBarLayout, int verticalOffset)
 
 		}
 
+		internal void Disconnect()
+		{
+			if (_shellContext?.Shell != null)
+				_shellContext.Shell.PropertyChanged -= OnShellPropertyChanged;
+
+			if (_flyoutHeader != null)
+				_flyoutHeader.MeasureInvalidated -= OnFlyoutHeaderMeasureInvalidated;
+
+			_flyoutHeader = null;
+
+			if (_footerView != null)
+				_footerView.View = null;
+
+			_headerView?.Disconnect();
+			DisconnectRecyclerView();
+
+			if (_contentView != null)
+				_contentView.View = null;
+		}
+
 		protected override void Dispose(bool disposing)
 		{
 			if (_disposed)
@@ -601,10 +634,7 @@ protected override void Dispose(bool disposing)
 
 			if (disposing)
 			{
-				_shellContext.Shell.PropertyChanged -= OnShellPropertyChanged;
-
-				if (_flyoutHeader != null)
-					_flyoutHeader.MeasureInvalidated -= OnFlyoutHeaderMeasureInvalidated;
+				Disconnect();
 
 				if (_appBar != null)
 				{
@@ -627,17 +657,13 @@ protected override void Dispose(bool disposing)
 					_contentView.View = null;
 
 				_flyoutContentView?.Dispose();
-				_headerView.Dispose();
+				_headerView?.Dispose();
 
-				if (_footerView != null)
-					_footerView.View = null;
-
-				_rootView.Dispose();
+				_rootView?.Dispose();
 				_defaultBackgroundColor?.Dispose();
 				_bgImage?.Dispose();
 
 				_contentView = null;
-				_flyoutHeader = null;
 				_rootView = null;
 				_headerView = null;
 				_shellContext = null;
@@ -715,17 +741,22 @@ protected override void Dispose(bool disposing)
 					return;
 
 				_isdisposed = true;
-				if (disposing)
-				{
-					if (View != null)
-						View.PropertyChanged -= OnViewPropertyChanged;
-				}
 
-				View = null;
+				if (disposing)
+					Disconnect();
 
 				base.Dispose(disposing);
 			}
 
+			internal void Disconnect()
+			{
+				if (View != null)
+				{
+					View.PropertyChanged -= OnViewPropertyChanged;
+					View = null;
+				}
+			}
+
 			internal void SetFlyoutHeaderBehavior(FlyoutHeaderBehavior flyoutHeaderBehavior)
 			{
 				if (_flyoutHeaderBehavior == flyoutHeaderBehavior)

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellFragmentContainer.cs

@@ -29,11 +29,20 @@ public override AView OnCreateView(LayoutInflater inflater, ViewGroup container,
 			// Handler and MauiContext
 			// But we want to update the inflater and ChildFragmentManager to match
 			// the handlers new home			
-			if (_page?.Handler?.MauiContext is MauiContext scopedMauiContext)
+			if (_page.Handler?.MauiContext is MauiContext scopedMauiContext)
 			{
-				scopedMauiContext.AddWeakSpecific(ChildFragmentManager);
-				scopedMauiContext.AddWeakSpecific(inflater);
-				mauiContext = scopedMauiContext;
+				// If this page comes to us from a different activity then don't reuse it
+				// disconnect the handler so it can recreate against new MauiContext
+				if (scopedMauiContext.GetActivity() == Context.GetActivity())
+				{
+					scopedMauiContext.AddWeakSpecific(ChildFragmentManager);
+					scopedMauiContext.AddWeakSpecific(inflater);
+					mauiContext = scopedMauiContext;
+				}
+				else
+				{
+					_page.Handler.DisconnectHandler();
+				}
 			}
 
 			mauiContext ??= _mauiContext.MakeScoped(layoutInflater: inflater, fragmentManager: ChildFragmentManager);

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellFragmentStateAdapter.cs

@@ -49,6 +49,7 @@ public void OnItemsCollectionChanged(object sender, NotifyCollectionChangedEvent
 
 		public override Fragment CreateFragment(int position)
 		{
+
 			var shellContent = _items[position];
 			return new ShellFragmentContainer(shellContent, _mauiContext) { Arguments = Bundle.Empty };
 		}

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellItemRendererBase.cs

@@ -75,7 +75,7 @@ protected Page DisplayedPage
 			}
 		}
 
-		protected IShellContext ShellContext { get; }
+		protected IShellContext ShellContext { get; private set; }
 
 		protected ShellItem ShellItem { get; private set; }
 
@@ -84,6 +84,13 @@ protected virtual IShellObservableFragment CreateFragmentForPage(Page page)
 			return ShellContext.CreateFragmentForPage(page);
 		}
 
+		internal void Disconnect()
+		{
+			ShellSection = null;
+			DisplayedPage = null;
+			ShellContext = null;
+		}
+
 		void Destroy()
 		{
 			foreach (var item in _fragmentMap)

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellRenderer.cs

@@ -114,6 +114,7 @@ static Color ResolveThemeColor(Color light, Color dark)
 		IShellFlyoutRenderer _flyoutView;
 		FrameLayout _frameLayout;
 		IMauiContext _mauiContext;
+		bool _disposed;
 
 		event EventHandler<PropertyChangedEventArgs> _elementPropertyChanged;
 
@@ -345,6 +346,30 @@ void IElementHandler.Invoke(string command, object args)
 
 		void IElementHandler.DisconnectHandler()
 		{
+			if (_disposed)
+				return;
+
+			_disposed = true;
+
+			Element.PropertyChanged -= OnElementPropertyChanged;
+			Element.SizeChanged -= OnElementSizeChanged;
+			((IShellController)Element).RemoveAppearanceObserver(this);
+
+			if (_flyoutView is ShellFlyoutRenderer sfr)
+				sfr.Disconnect();
+			else
+				(_flyoutView as IDisposable)?.Dispose();
+
+			if (_currentView is ShellItemRendererBase sir)
+				sir.Disconnect();
+			else
+				_currentView.Dispose();
+
+			_currentView = null;
+
+			Element = null;
+
+			_disposed = true;
 		}
 
 		class SplitDrawable : Drawable
@@ -390,4 +415,4 @@ public override void SetColorFilter(ColorFilter colorFilter)
 		}
 
 	}
-}
+}

src/Controls/src/Core/HandlerImpl/Shell.Impl.cs

@@ -28,5 +28,14 @@ protected override void OnPropertyChanged([CallerMemberName] string propertyName
 			if (propertyName == Shell.FlyoutIsPresentedProperty.PropertyName)
 				Handler?.UpdateValue(nameof(IFlyoutView.IsPresented));
 		}
+
+#if ANDROID
+		protected override void OnHandlerChanging(HandlerChangingEventArgs args)
+		{
+			base.OnHandlerChanging(args);
+			args.OldHandler?.DisconnectHandler();
+		}
+
+#endif
 	}
 }

src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -11,3 +11,4 @@ override Microsoft.Maui.Controls.TemplatedView.MeasureOverride(double widthConst
 *REMOVED*override Microsoft.Maui.Controls.RadioButton.ArrangeOverride(Microsoft.Maui.Graphics.Rect bounds) -> Microsoft.Maui.Graphics.Size
 *REMOVED*override Microsoft.Maui.Controls.RadioButton.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
 *REMOVED*override Microsoft.Maui.Controls.FlexLayout.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+~override Microsoft.Maui.Controls.Shell.OnHandlerChanging(Microsoft.Maui.Controls.HandlerChangingEventArgs args) -> void

src/Controls/tests/DeviceTests/Elements/Shell/ShellTests.Android.cs

@@ -17,6 +17,8 @@
 using AndroidX.CoordinatorLayout.Widget;
 using AndroidX.Core.View;
 using static Microsoft.Maui.Controls.Platform.Compatibility.ShellFlyoutTemplatedContentRenderer;
+using Microsoft.Maui.DeviceTests.Stubs;
+using Microsoft.Maui.Handlers;
 
 namespace Microsoft.Maui.DeviceTests
 {
@@ -219,6 +221,44 @@ await CreateHandlerAndAddToWindow<ShellRenderer>(shell, async (handler) =>
 			});
 		}
 
+
+		[Fact]
+		public async Task SwappingOutAndroidContextDoesntCrash()
+		{
+			SetupBuilder();
+
+			var shell = await CreateShellAsync(shell =>
+			{
+				shell.Items.Add(new FlyoutItem() { Route = "FlyoutItem1", Items = { new ContentPage() }, Title = "Flyout Item" });
+				shell.Items.Add(new FlyoutItem() { Route = "FlyoutItem2", Items = { new ContentPage() }, Title = "Flyout Item" });
+			});
+
+			var window = new Controls.Window(shell);
+			var mauiContextStub1 = new ContextStub(MauiApp.Services);
+			var activity = mauiContextStub1.GetActivity();
+			mauiContextStub1.Context = new ContextThemeWrapper(activity, Resource.Style.Maui_MainTheme_NoActionBar);
+
+			await CreateHandlerAndAddToWindow<IWindowHandler>(window, async (handler) =>
+			{
+				await OnLoadedAsync(shell.CurrentPage);
+				await OnNavigatedToAsync(shell.CurrentPage);
+				await Task.Delay(100);
+				await shell.GoToAsync("//FlyoutItem2");
+			}, mauiContextStub1);
+
+			var mauiContextStub2 = new ContextStub(MauiApp.Services);
+			mauiContextStub2.Context = new ContextThemeWrapper(activity, Resource.Style.Maui_MainTheme_NoActionBar);
+
+			await CreateHandlerAndAddToWindow<IWindowHandler>(window, async (handler) =>
+			{
+				await OnLoadedAsync(shell.CurrentPage);
+				await OnNavigatedToAsync(shell.CurrentPage);
+				await Task.Delay(100);
+				await shell.GoToAsync("//FlyoutItem1");
+				await shell.GoToAsync("//FlyoutItem2");
+			}, mauiContextStub2);
+		}
+
 		protected AView GetFlyoutPlatformView(ShellRenderer shellRenderer)
 		{
 			var drawerLayout = GetDrawerLayout(shellRenderer);

src/Controls/tests/DeviceTests/HandlerTestBase.Android.cs

@@ -39,9 +39,10 @@ public AView GetSemanticPlatformElement(IViewHandler viewHandler)
 		}
 
 		static Drawable _decorDrawable;
-		Task SetupWindowForTests<THandler>(IWindow window, Func<Task> runTests)
+		Task SetupWindowForTests<THandler>(IWindow window, Func<Task> runTests, IMauiContext mauiContext = null)
 			where THandler : class, IElementHandler
 		{
+			mauiContext ??= MauiContext;
 			return InvokeOnMainThreadAsync(async () =>
 			{
 				AViewGroup rootView = MauiContext.Context.GetActivity().Window.DecorView as AViewGroup;