[Windows] Fix crash when navigating pages

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;
+		ContentControl? _previousContent;
 		bool _connected;
 
 		protected NavigationRootManager WindowManager => _mauiContext.GetNavigationRootManager();
@@ -156,31 +154,41 @@ void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)
 				return;
 
 			var nv = NavigationView;
-			ContentPresenter? presenter;
+			ContentControl? presenter;
 
 			if (page.Content == null)
 			{
-				presenter = new ContentPresenter()
+				presenter = new ContentControl()
 				{
 					HorizontalAlignment = UI.Xaml.HorizontalAlignment.Stretch,
 					VerticalAlignment = UI.Xaml.VerticalAlignment.Stretch
 				};
 
+				// It's possible that the unloaded event didn't happen yet, so force clear the content
+				if (_previousContent is not null)
+				{
+					_previousContent.Content = null;
+					_previousContent = null;
+				}
+
+				presenter.Unloaded += Presenter_Unloaded;
 				page.Content = presenter;
 			}
 			else
 			{
-				presenter = page.Content as ContentPresenter;
+				presenter = page.Content as ContentControl;
 			}
 
 			// 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 +198,8 @@ void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)
 
 			_pendingNavigationFinished = () =>
 			{
+				_previousContent = presenter;
+
 				if (presenter?.Content is not FrameworkElement pc)
 				{
 					FireNavigationFinished();
@@ -208,6 +218,21 @@ void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)
 			fe.OnLoaded(FirePendingNavigationFinished);
 		}
 
+		/// <summary>
+		/// There's some bug in our code, or the lifecycle of ContentControl, that is causing the content to
+		/// never be removed from the parent...
+		/// </summary>
+		/// <param name="sender"></param>
+		/// <param name="e"></param>
+		private void Presenter_Unloaded(object sender, RoutedEventArgs e)
+		{
+			if (sender is ContentControl control)
+			{
+				control.Content = null;
+				control.Unloaded -= Presenter_Unloaded;
+			}
+		}
+
 		void FireNavigationFinished()
 		{
 			_pendingNavigationFinished = null;