[controls] fix memory leaks in Page & navigation

Fixes: dotnet#13520
Context: https://github.com/danardelean/MauiTestFinalizer

In the above sample, you can see `Page` objects leaking while using
Shell navigation. I was able to reproduce this in a test with both
Shell & `NavigationPage` such as:

    [Fact(DisplayName = "NavigationPage Does Not Leak")]
    public async Task DoesNotLeak()
    {
        SetupBuilder();
        WeakReference pageReference = null;
        var navPage = new NavigationPage(new ContentPage { Title = "Page 1" });

        await CreateHandlerAndAddToWindow<WindowHandlerStub>(new Window(navPage), async (handler) =>
        {
            var page = new ContentPage { Title = "Page 2" };
            pageReference = new WeakReference(page);
            await navPage.Navigation.PushAsync(page);
            await navPage.Navigation.PopAsync();
        });

        await Task.Yield();
        GC.Collect();
        GC.WaitForPendingFinalizers();
        Assert.NotNull(pageReference);
        Assert.False(pageReference.IsAlive, "Page should not be alive!");
    }

To summarize:

* Customer's sample only leaks on iOS/Catalyst

* My Shell/NavigationPage tests leak on Android/iOS/Catalyst

Comparing various GC heap dumps in Visual Studio, I was able to find
the sources of these issues. I'll try to list them.

* Controls.Core
    * `Window.OnPageChanged()` should unset `_menuBarTracker.Target`
* Windows
    * `ContentViewHandler.DisconnectHandler` should unset
      `platformView.CrossPlatformMeasure` and
      `platformView.CrossPlatformArrange`.
* Android
    * `ContentViewHandler.DisconnectHandler` should unset
      `platformView.CrossPlatformMeasure` and
      `platformView.CrossPlatformArrange`.
    * `NavigationViewFragment.OnDestroy()` should unset `_currentView`
      and `_fragmentContainerView`
* iOS/Catalyst
    * `ContentViewHandler.DisconnectHandler` should unset
      `platformView.CrossPlatformMeasure` and
      `platformView.CrossPlatformArrange`.
    * `ContentViewHandler.DisconnectHandler` should call
      `RemoveFromSuperview()`

After these changes, my tests pass! They literally would not pass
without fixing all of the above... Each issue I found while reviewing
GC dumps.

Other test changes:

* `ControlsHandlerTestBase.Windows.cs` needed some `null` checks
* `ShellTests` needed an `&& !MACCATALYST` to build for MacCatalyst

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

@@ -598,6 +598,7 @@ void OnPageChanged(Page? oldPage, Page? newPage)
  {
  if (oldPage != null)
  {
+ _menuBarTracker.Target = null;
  InternalChildren.Remove(oldPage);
  oldPage.HandlerChanged -= OnPageHandlerChanged;
  oldPage.HandlerChanging -= OnPageHandlerChanging;

src/Controls/tests/DeviceTests/ControlsHandlerTestBase.Windows.cs

@@ -40,10 +40,10 @@ Task SetupWindowForTests<THandler>(IWindow window, Func<Task> runTests, IMauiCon
  }
  finally
  {
- window.Handler.DisconnectHandler();
+ window.Handler?.DisconnectHandler();
  await Task.Delay(10);
  newWindow?.Close();
- appStub.Handler.DisconnectHandler();
+ appStub.Handler?.DisconnectHandler();
  }
  });
  }

src/Controls/tests/DeviceTests/Elements/NavigationPage/NavigationPageTests.cs

@@ -287,5 +287,28 @@ await CreateHandlerAndAddToWindow<WindowHandlerStub>(new Window(navPage), async
  };
  });
  }
+
+ [Fact(DisplayName = "NavigationPage Does Not Leak")]
+ public async Task DoesNotLeak()
+ {
+ SetupBuilder();
+ WeakReference pageReference = null;
+ var navPage = new NavigationPage(new ContentPage { Title = "Page 1" });
+
+ await CreateHandlerAndAddToWindow<WindowHandlerStub>(new Window(navPage), async (handler) =>
+ {
+ var page = new ContentPage { Title = "Page 2" };
+ pageReference = new WeakReference(page);
+ await navPage.Navigation.PushAsync(page);
+ await navPage.Navigation.PopAsync();
+ });
+
+ await Task.Yield();
+ GC.Collect();
+ GC.WaitForPendingFinalizers();
+
+ Assert.NotNull(pageReference);
+ Assert.False(pageReference.IsAlive, "Page should not be alive!");
+ }
  }
 }

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

@@ -660,7 +660,7 @@ await CreateHandlerAndAddToWindow<ShellHandler>(shell, async (handler) =>
  });
  }
 
-#if !IOS
+#if !IOS && !MACCATALYST
  [Fact]
  public async Task ChangingToNewMauiContextDoesntCrash()
  {
@@ -917,6 +917,40 @@ await CreateHandlerAndAddToWindow<WindowHandlerStub>(new Window(navPage), async
  }
 #endif
 
+ [Fact(DisplayName = "Pages Do Not Leak")]
+ public async Task PagesDoNotLeak()
+ {
+ SetupBuilder();
+ var shell = await CreateShellAsync(shell =>
+ {
+ shell.CurrentItem = new ContentPage() { Title = "Page 1" };
+ });
+
+ WeakReference pageReference = null;
+
+ await CreateHandlerAndAddToWindow<ShellHandler>(shell, async (handler) =>
+ {
+ await OnLoadedAsync(shell.CurrentPage);
+
+ var page = new ContentPage { Title = "Page 2" };
+ pageReference = new WeakReference(page);
+
+ await shell.Navigation.PushAsync(page);
+ await shell.Navigation.PopAsync();
+ });
+
+ // 3 GCs were required in Android API 23, 2 worked otherwise
+ for (int i = 0; i < 3; i++)
+ {
+ await Task.Yield();
+ GC.Collect();
+ GC.WaitForPendingFinalizers();
+ }
+
+ Assert.NotNull(pageReference);
+ Assert.False(pageReference.IsAlive, "Page should not be alive!");
+ }
+
  protected Task<Shell> CreateShellAsync(Action<Shell> action) =>
  InvokeOnMainThreadAsync(() =>
  {

src/Core/src/Handlers/ContentView/ContentViewHandler.Android.cs

@@ -52,6 +52,8 @@ public static void MapContent(IContentViewHandler handler, IContentView page)
  protected override void DisconnectHandler(ContentViewGroup platformView)
  {
  // If we're being disconnected from the xplat element, then we should no longer be managing its children
+ platformView.CrossPlatformMeasure = null;
+ platformView.CrossPlatformArrange = null;
  platformView.RemoveAllViews();
  base.DisconnectHandler(platformView);
  }

src/Core/src/Handlers/ContentView/ContentViewHandler.Windows.cs

@@ -49,5 +49,12 @@ public static void MapContent(IContentViewHandler handler, IContentView page)
  {
  UpdateContent(handler);
  }
+
+ protected override void DisconnectHandler(ContentPanel platformView)
+ {
+ platformView.CrossPlatformMeasure = null;
+ platformView.CrossPlatformArrange = null;
+ base.DisconnectHandler(platformView);
+ }
  }
 }

src/Core/src/Handlers/ContentView/ContentViewHandler.iOS.cs

@@ -53,5 +53,15 @@ public static void MapContent(IContentViewHandler handler, IContentView page)
  {
  UpdateContent(handler);
  }
+
+ protected override void DisconnectHandler(ContentView platformView)
+ {
+ platformView.CrossPlatformMeasure = null;
+ platformView.CrossPlatformArrange = null;
+ // TODO: this specific call fixes leaks in iOS/Catalyst
+ // But it doesn't feel quite right
+ platformView.RemoveFromSuperview();
+ base.DisconnectHandler(platformView);
+ }
  }
 }

src/Core/src/Platform/Android/Navigation/NavigationViewFragment.cs

@@ -78,6 +78,14 @@ public override void OnResume()
  base.OnResume();
  }
 
+ public override void OnDestroy()
+ {
+ _currentView = null;
+ _fragmentContainerView = null;
+
+ base.OnDestroy();
+ }
+
  public override Animation OnCreateAnimation(int transit, bool enter, int nextAnim)
  {
  int id = 0;

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

@@ -10,6 +10,7 @@ override Microsoft.Maui.Handlers.EditorHandler.PlatformArrange(Microsoft.Maui.Gr
 override Microsoft.Maui.Handlers.RadioButtonHandler.PlatformArrange(Microsoft.Maui.Graphics.Rect frame) -> void
 override Microsoft.Maui.Layouts.FlexBasis.Equals(object? obj) -> bool
 override Microsoft.Maui.Layouts.FlexBasis.GetHashCode() -> int
+override Microsoft.Maui.Platform.NavigationViewFragment.OnDestroy() -> void
 override Microsoft.Maui.SizeRequest.Equals(object? obj) -> bool
 override Microsoft.Maui.SizeRequest.GetHashCode() -> int
 static Microsoft.Maui.FontSize.operator !=(Microsoft.Maui.FontSize left, Microsoft.Maui.FontSize right) -> bool

src/Core/src/PublicAPI/net-ios/PublicAPI.Unshipped.txt

@@ -7,6 +7,7 @@ Microsoft.Maui.Hosting.MauiApp.DisposeAsync() -> System.Threading.Tasks.ValueTas
 Microsoft.Maui.Layouts.FlexBasis.Equals(Microsoft.Maui.Layouts.FlexBasis other) -> bool
 Microsoft.Maui.LifecycleEvents.iOSLifecycle.PerformFetch
 Microsoft.Maui.SizeRequest.Equals(Microsoft.Maui.SizeRequest other) -> bool
+override Microsoft.Maui.Handlers.ContentViewHandler.DisconnectHandler(Microsoft.Maui.Platform.ContentView! platformView) -> void
 override Microsoft.Maui.Handlers.SwipeItemButton.Frame.get -> CoreGraphics.CGRect
 override Microsoft.Maui.Handlers.SwipeItemButton.Frame.set -> void
 override Microsoft.Maui.Handlers.SwipeItemMenuItemHandler.ConnectHandler(UIKit.UIButton! platformView) -> void

src/Core/src/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt

@@ -6,6 +6,7 @@ Microsoft.Maui.IApplication.UserAppTheme.get -> Microsoft.Maui.ApplicationModel.
 Microsoft.Maui.Hosting.MauiApp.DisposeAsync() -> System.Threading.Tasks.ValueTask
 Microsoft.Maui.Layouts.FlexBasis.Equals(Microsoft.Maui.Layouts.FlexBasis other) -> bool
 Microsoft.Maui.SizeRequest.Equals(Microsoft.Maui.SizeRequest other) -> bool
+override Microsoft.Maui.Handlers.ContentViewHandler.DisconnectHandler(Microsoft.Maui.Platform.ContentView! platformView) -> void
 override Microsoft.Maui.Handlers.SwipeItemButton.Frame.get -> CoreGraphics.CGRect
 override Microsoft.Maui.Handlers.SwipeItemButton.Frame.set -> void
 override Microsoft.Maui.Handlers.SwipeItemMenuItemHandler.ConnectHandler(UIKit.UIButton! platformView) -> void

src/Core/src/PublicAPI/net-windows/PublicAPI.Unshipped.txt

@@ -4,6 +4,7 @@ Microsoft.Maui.Hosting.MauiApp.DisposeAsync() -> System.Threading.Tasks.ValueTas
 Microsoft.Maui.Layouts.FlexBasis.Equals(Microsoft.Maui.Layouts.FlexBasis other) -> bool
 Microsoft.Maui.Platform.MauiWebView.MauiWebView(Microsoft.Maui.Handlers.WebViewHandler! handler) -> void
 Microsoft.Maui.SizeRequest.Equals(Microsoft.Maui.SizeRequest other) -> bool
+override Microsoft.Maui.Handlers.ContentViewHandler.DisconnectHandler(Microsoft.Maui.Platform.ContentPanel! platformView) -> void
 override Microsoft.Maui.Layouts.FlexBasis.Equals(object? obj) -> bool
 override Microsoft.Maui.Layouts.FlexBasis.GetHashCode() -> int
 override Microsoft.Maui.SizeRequest.Equals(object? obj) -> bool