[windows] Fixed Rapid change of selected tab results in crash. (#33113)

### Root Cause
On Windows, `TabbedPage` uses WinUI `Frame` navigation to display each
tab’s content. Each tab’s platform view (native UI element) is hosted
inside a WinUI `Page` through a `ContentPresenter`.
During rapid tab switching, the platform view is reassigned to a new
WinUI `Page` while still attached to the previous one. WinUI does not
allow a UI element to exist in two visual trees simultaneously, which
causes the crash.
 
### Description of Change
Added a `_displayedPage` tracking field to maintain the correct
displayed MAUI Page during navigation, allowing `NavigateToPage` to skip
early if the requested page is already displayed and avoid redundant
navigation. The method also now clears the previous WinUI Page’s
`ContentPresenter` to explicitly detach the platform view and prevent
the “element already has a parent” WinUI error. In
`UpdateCurrentPageContent`, a skip guard avoids reassigning content that
is already set, while `_displayedPage` is updated only after successful
content assignment. Finally, OnHandlerDisconnected resets
`_displayedPage` to null to ensure proper cleanup and prevent stale
references.

### Issues Fixed
Fixes #32824 
 
Tested the behaviour in the following platforms
- [x] Android
- [x] Windows
- [x] iOS
- [x] Mac

### Output Video
| Before Issue Fix | After Issue Fix |
|------------------|-----------------|
| <img width="350" alt="withoutfix"
src="https://github.com/user-attachments/assets/4ae17a81-a399-4cd6-856d-ca4938cb683b"
/> | <img width="350" alt="withfix"
src="https://github.com/user-attachments/assets/5927a164-22d8-45bc-a910-003bfbc1927a"
/> |

Author: praveenkumarkarunanithi

src/Controls/src/Core/TabbedPage/TabbedPage.Windows.cs

@@ -19,6 +19,7 @@ public partial class TabbedPage
 		NavigationRootManager? _navigationRootManager;
 		WFrame? _navigationFrame;
 		bool _connectedToHandler;
+		Page? _displayedPage;
 		WFrame NavigationFrame => _navigationFrame ?? throw new ArgumentNullException(nameof(NavigationFrame));
 		IMauiContext MauiContext => this.Handler?.MauiContext ?? throw new InvalidOperationException("MauiContext cannot be null here");
 
@@ -177,6 +178,7 @@ void OnHandlerDisconnected(ElementHandler? elementHandler)
 			_navigationView = null;
 			_navigationRootManager = null;
 			_navigationFrame = null;
+			_displayedPage = null;
 		}
 
 		void OnTabbedPageAppearing(object? sender, EventArgs e)
@@ -255,8 +257,15 @@ void OnSelectedMenuItemChanged(NavigationView sender, NavigationViewSelectionCha
 
 		void NavigateToPage(Page page)
 		{
-			FrameNavigationOptions navOptions = new FrameNavigationOptions();
+			if (_displayedPage == page)
+				return;
+
+			// Detach content from old page to prevent "Element is already the child of another element" error
+			if (NavigationFrame.Content is WPage oldPage && oldPage.Content is WContentPresenter oldPresenter)
+				oldPresenter.Content = null;
+
 			CurrentPage = page;
+			FrameNavigationOptions navOptions = new FrameNavigationOptions();
 			navOptions.IsNavigationStackEnabled = false;
 			NavigationFrame.NavigateToType(typeof(WPage), null, navOptions);
 		}
@@ -270,7 +279,7 @@ void UpdateCurrentPageContent()
 
 		void UpdateCurrentPageContent(WPage page)
 		{
-			if (MauiContext == null)
+			if (MauiContext == null || _displayedPage == CurrentPage)
 				return;
 
 			WContentPresenter? presenter;
@@ -297,6 +306,7 @@ void UpdateCurrentPageContent(WPage page)
 				return;
 
 			presenter.Content = _currentPage.ToPlatform(MauiContext);
+			_displayedPage = CurrentPage;
 		}
 
 		void OnNavigated(object sender, UI.Xaml.Navigation.NavigationEventArgs e)

src/Controls/tests/DeviceTests/Elements/TabbedPage/TabbedPageTests.Windows.cs

@@ -2,6 +2,7 @@
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using System.Reflection;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Maui;
 using Microsoft.Maui.Controls;
@@ -12,7 +13,10 @@
 using Microsoft.Maui.Hosting;
 using Microsoft.Maui.Platform;
 using Xunit;
+using WContentPresenter = Microsoft.UI.Xaml.Controls.ContentPresenter;
+using WFrame = Microsoft.UI.Xaml.Controls.Frame;
 using WFrameworkElement = Microsoft.UI.Xaml.FrameworkElement;
+using WPage = Microsoft.UI.Xaml.Controls.Page;
 using WSolidColorBrush = Microsoft.UI.Xaml.Media.SolidColorBrush;
 
 namespace Microsoft.Maui.DeviceTests
@@ -197,5 +201,39 @@ await AssertionExtensions.AssertTabItemTextDoesNotContainColor(
 					tabText, iconColor, tabbedPage.FindMauiContext());
 			}
 		}
+
+		[Fact(DisplayName = "Issue 32824 - Tab Switch Clears Old Content To Prevent Crash")]
+		public async Task TabSwitchClearsOldContentToPreventCrash()
+		{
+			// https://github.com/dotnet/maui/issues/32824
+			// When switching tabs, the old ContentPresenter.Content must be cleared
+			// before navigation to prevent "Element is already the child of another element" crash.
+			SetupBuilder();
+
+			var page1 = new ContentPage { Title = "Tab 1", Content = new Label { Text = "Page 1" } };
+			var page2 = new ContentPage { Title = "Tab 2", Content = new Label { Text = "Page 2" } };
+			var tabbedPage = new TabbedPage { Children = { page1, page2 } };
+
+			await CreateHandlerAndAddToWindow<TabbedViewHandler>(tabbedPage, handler =>
+			{
+				var frame = typeof(TabbedPage)
+					.GetField("_navigationFrame", BindingFlags.NonPublic | BindingFlags.Instance)
+					?.GetValue(tabbedPage) as WFrame;
+
+				Assert.NotNull(frame);
+
+				var oldPresenter = (frame.Content as WPage)?.Content as WContentPresenter;
+				Assert.NotNull(oldPresenter);
+				Assert.NotNull(oldPresenter.Content);
+
+				// Switch tabs - oldPresenter.Content should be cleared before navigation
+				tabbedPage.CurrentPage = page2;
+
+				//old presenter content must be null to prevent crash
+				Assert.Null(oldPresenter.Content);
+
+				return Task.CompletedTask;
+			});
+		}
 	}
 }