[release/9.0.1xx-sr1] [release/9.0.1xx] [Windows] Fix crash when navi…

…gating pages (#26108)

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

@@ -541,6 +541,31 @@ await CreateHandlerAndAddToWindow<ShellHandler>(shell, async (handler) =>
 			});
 		}
 
+		[Fact(DisplayName = "Navigate back and forth doesn't crash")]
+		public async Task NavigateBackAndForthDoesntCrash()
+		{
+			SetupBuilder();
+
+			var shell = await CreateShellAsync(shell =>
+			{
+				shell.CurrentItem = new ContentPage();
+			});
+
+			await CreateHandlerAndAddToWindow<ShellHandler>(shell, async (handler) =>
+			{
+				var secondPage = new ContentPage();
+
+				for (int i = 0; i < 5; i++)
+				{
+					await shell.Navigation.PushAsync(secondPage, false);
+					await Task.Delay(100);
+					await shell.Navigation.PopToRootAsync(false);
+					await Task.Delay(100);
+				}
+				Assert.NotNull(shell.Handler);
+			});
+		}
+
 		[Fact(DisplayName = "Shell Toolbar With Only MenuBarItems Is Visible")]
 		public async Task ShellToolbarWithOnlyMenuBarItemsIsVisible()
 		{

src/Core/src/Platform/Windows/StackNavigationManager.cs

@@ -1,9 +1,6 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 using System.Threading;
-using System.Threading.Tasks;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Media.Animation;
@@ -17,6 +14,7 @@ public class StackNavigationManager
 		IMauiContext _mauiContext;
 		Frame? _navigationFrame;
 		Action? _pendingNavigationFinished;
+		ContentPresenter? _previousContent;
 		bool _connected;
 
 		protected NavigationRootManager WindowManager => _mauiContext.GetNavigationRootManager();
@@ -58,6 +56,12 @@ public virtual void Disconnect(IStackNavigation navigationView, Frame navigation
 			FirePendingNavigationFinished();
 			_navigationFrame = null;
 			NavigationView = null;
+
+			if (_previousContent is not null)
+			{
+				_previousContent.Content = null;
+				_previousContent = null;
+			}
 		}
 
 		public virtual void NavigateTo(NavigationRequest args)
@@ -166,6 +170,14 @@ void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)
 					VerticalAlignment = UI.Xaml.VerticalAlignment.Stretch
 				};
 
+				// There's some bug in our code, or the lifecycle of ContentControl, that is causing the content to
+				// never be removed from the parent...
+				if (_previousContent is not null)
+				{
+					_previousContent.Content = null;
+					_previousContent = null;
+				}
+
 				page.Content = presenter;
 			}
 			else
@@ -174,13 +186,15 @@ void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)
 			}
 
 			// At this point if the Content isn't a ContentPresenter the user has replaced
-			// the conent so we just let them take control
+			// the content so we just let them take control
 			if (presenter == null || _currentPage == null)
 				return;
 
+			var platformPage = _currentPage.ToPlatform(MauiContext);
+
 			try
 			{
-				presenter.Content = _currentPage.ToPlatform(MauiContext);
+				presenter.Content = platformPage;
 			}
 			catch (Exception)
 			{
@@ -190,6 +204,8 @@ void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)
 
 			_pendingNavigationFinished = () =>
 			{
+				_previousContent = presenter;
+
 				if (presenter?.Content is not FrameworkElement pc)
 				{
 					FireNavigationFinished();