[windows] fix memory leak in MauiWinUIWindow (#23327)

src/Controls/src/Core/Platform/AlertManager/AlertManager.Windows.cs

@@ -26,10 +26,10 @@ internal void Unsubscribe(Window window)
 		{
 			IMauiContext? mauiContext = window?.Handler?.MauiContext;
 			var platformWindow = mauiContext?.GetPlatformWindow();
-			if (platformWindow == null)
-				return;
 
-			var toRemove = Subscriptions.Where(s => s.PlatformView == platformWindow).ToList();
+			var toRemove = platformWindow is null ?
+				Subscriptions.Where(s => s.VirtualView == window).ToList() :
+				Subscriptions.Where(s => s.PlatformView == platformWindow).ToList();
 
 			foreach (AlertRequestHelper alertRequestHelper in toRemove)
 			{

src/Controls/tests/DeviceTests/Memory/MemoryTests.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Threading.Tasks;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Maui.Controls;
 using Microsoft.Maui.Controls.Handlers;
 using Microsoft.Maui.Controls.Handlers.Compatibility;
@@ -404,6 +405,36 @@ await CreateHandlerAndAddToWindow<WindowHandlerStub>(new Window(page), async _ =
 		await AssertionExtensions.WaitForGC(references[0], references[1], references[2]);
 	}
 
+	[Fact("Window Does Not Leak")]
+	public async Task WindowDoesNotLeak()
+	{
+		SetupBuilder();
+
+		var references = new List<WeakReference>();
+
+		{
+			var page = new ContentPage();
+			var window = new Window(page);
+			await CreateHandlerAndAddToWindow(window, async () =>
+			{
+				await OnLoadedAsync(page);
+				references.Add(new(window));
+				references.Add(new(window.Handler));
+
+				// NOTE: the PlatformView in this case remains alive in the test application:
+				// Activity on Android, Microsoft.UI.Xaml.Window on Windows, etc.
+				//references.Add(new(window.Handler.PlatformView));
+
+				if (MauiContext.Services.GetService<IApplication>() is ApplicationStub app)
+				{
+					app.SetWindow(null);
+				}
+			});
+		}
+
+		await AssertionExtensions.WaitForGC(references.ToArray());
+	}
+
 #if IOS
 	[Fact]
 	public async Task ResignFirstResponderTouchGestureRecognizer()

src/Core/src/Platform/Windows/MauiWinUIWindow.cs

@@ -165,7 +165,7 @@ void OnWindowMessage(object? sender, WindowMessageEventArgs e)
 						var rootManager = Window?.Handler?.MauiContext?.GetNavigationRootManager();
 						if (rootManager != null)
 						{
-							rootManager?.SetTitleBarVisibility(hasTitleBar);
+							rootManager?.SetTitleBarVisibility(this, hasTitleBar);
 						}
 					}
 				}

src/Core/src/Platform/Windows/NavigationRootManager.cs

@@ -7,26 +7,26 @@ namespace Microsoft.Maui.Platform
 {
 	public partial class NavigationRootManager
 	{
-		Window _platformWindow;
+		readonly WeakReference<Window> _platformWindow;
 		WindowRootView _rootView;
 		bool _disconnected = true;
 		internal event EventHandler? OnApplyTemplateFinished;
 
 		public NavigationRootManager(Window platformWindow)
 		{
-			_platformWindow = platformWindow;
+			_platformWindow = new(platformWindow);
 			_rootView = new WindowRootView();
 			_rootView.BackRequested += OnBackRequested;
 			_rootView.OnApplyTemplateFinished += WindowRootViewOnApplyTemplateFinished;
 
-			var titleBar = _platformWindow.GetAppWindow()?.TitleBar;
+			var titleBar = platformWindow.GetAppWindow()?.TitleBar;
 			if (titleBar is not null)
 			{
-				SetTitleBarVisibility(titleBar.ExtendsContentIntoTitleBar);
+				SetTitleBarVisibility(platformWindow, titleBar.ExtendsContentIntoTitleBar);
 			}
 		}
 
-		internal void SetTitleBarVisibility(bool isVisible)
+		internal void SetTitleBarVisibility(Window platformWindow, bool isVisible)
 		{
 			// https://learn.microsoft.com/en-us/windows/apps/design/basics/titlebar-design
 			// Standard title bar height is 32px
@@ -35,10 +35,10 @@ internal void SetTitleBarVisibility(bool isVisible)
 			var appbarHeight = isVisible ? 32 : 0;
 			if (isVisible && UI.Windowing.AppWindowTitleBar.IsCustomizationSupported())
 			{
-				var titleBar = _platformWindow.GetAppWindow()?.TitleBar;
+				var titleBar = platformWindow.GetAppWindow()?.TitleBar;
 				if (titleBar is not null)
 				{
-					var density = _platformWindow.GetDisplayDensity();
+					var density = platformWindow.GetDisplayDensity();
 					appbarHeight = (int)(titleBar.Height / density);
 				}
 			}
@@ -55,7 +55,7 @@ void WindowRootViewOnWindowTitleBarContentSizeChanged(object? sender, EventArgs
 			if (_disconnected)
 				return;
 
-			_platformWindow?
+			_platformWindow.GetTargetOrDefault()?
 				.GetWindow()?
 				.Handler?
 				.UpdateValue(nameof(IWindow.TitleBarDragRectangles));
@@ -66,7 +66,7 @@ void WindowRootViewOnApplyTemplateFinished(object? sender, System.EventArgs e) =
 
 		void OnBackRequested(NavigationView sender, NavigationViewBackRequestedEventArgs args)
 		{
-			_platformWindow
+			_platformWindow.GetTargetOrDefault()?
 				.GetWindow()?
 				.BackButtonClicked();
 		}
@@ -94,9 +94,9 @@ public virtual void Connect(UIElement platformView)
 				Content = platformView
 			};
 
-			if (_disconnected)
+			if (_disconnected && _platformWindow.TryGetTarget(out var platformWindow))
 			{
-				_platformWindow.Activated += OnWindowActivated;
+				platformWindow.Activated += OnWindowActivated;
 				_disconnected = false;
 			}
 
@@ -106,7 +106,10 @@ public virtual void Connect(UIElement platformView)
 		public virtual void Disconnect()
 		{
 			_rootView.OnWindowTitleBarContentSizeChanged -= WindowRootViewOnWindowTitleBarContentSizeChanged;
-			_platformWindow.Activated -= OnWindowActivated;
+			if (_platformWindow.TryGetTarget(out var platformWindow))
+			{
+				platformWindow.Activated -= OnWindowActivated;
+			}
 			SetToolbar(null);
 
 			if (_rootView.Content is RootNavigationView navView)