- fix up fragment management

src/Compatibility/Core/src/Android/AppCompat/FlyoutPageContainer.cs

@@ -222,7 +222,7 @@ protected override void Dispose(bool disposing)
 
 			if (disposing)
 			{
-				if (_currentFragment != null && !FragmentManager.IsDestroyed())
+				if (_currentFragment != null && !FragmentManager.IsDestroyed(Context))
 				{
 					FragmentTransaction transaction = FragmentManager.BeginTransactionEx();
 					transaction.RemoveEx(_currentFragment);

src/Compatibility/Core/src/Android/AppCompat/FormsFragmentPagerAdapter.cs

@@ -84,7 +84,7 @@ protected override void Dispose(bool disposing)
 
 				_page = null;
 
-				if (!_fragmentManager.IsDestroyed())
+				if (!_fragmentManager.IsDestroyed(_page?.Handler?.MauiContext?.Context))
 				{
 					FragmentTransaction transaction = _fragmentManager.BeginTransactionEx();
 

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellFragmentContainer.cs

@@ -22,9 +22,7 @@ public ShellFragmentContainer(ShellContent shellContent, IMauiContext mauiContex
 		public override AView OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
 		{
 			_page = ((IShellContentController)ShellContentTab).GetOrCreateContent();
-
-			var platformView =
-				_page.ToPlatform(_mauiContext, RequireContext(), inflater, ChildFragmentManager);
+			_page.ToPlatform(_mauiContext, RequireContext(), inflater, ChildFragmentManager);
 
 			return new ShellPageContainer(RequireContext(), (IPlatformViewHandler)_page.Handler, true)
 			{

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

@@ -207,6 +207,10 @@ async Task SendHandlerUpdateAsync(
 				// This task completes once the handler calls INavigationView.Finished
 				await currentNavRequestTaskSource.Task;
 			}
+			catch
+			{
+				throw;
+			}
 			finally
 			{
 				if (Interlocked.Decrement(ref _waitingCount) == 0)

src/Controls/src/Core/Platform/Android/FragmentContainer.cs

@@ -18,12 +18,7 @@ internal class FragmentContainer : Fragment
 		AView _pageContainer;
 		ViewGroup _parent;
 
-		public FragmentContainer(IMauiContext mauiContext)
-		{
-			_mauiContext = mauiContext;
-		}
-
-		public FragmentContainer(Page page, IMauiContext mauiContext) : this(mauiContext)
+		public FragmentContainer(Page page, IMauiContext mauiContext)
 		{
 			_pageRenderer = new WeakReference(page);
 			_mauiContext = mauiContext;
@@ -57,6 +52,13 @@ public override AView OnCreateView(LayoutInflater inflater, ViewGroup container,
 			return null;
 		}
 
+		public override void OnDestroy()
+		{
+			base.OnDestroy();
+			if (Context.IsDestroyed())
+				Page?.Handler?.DisconnectHandler();
+		}
+
 		public override void OnResume()
 		{
 			if (_pageContainer == null)

src/Controls/src/Core/Platform/Android/MultiPageFragmentStateAdapter.cs

@@ -1,13 +1,20 @@
+#nullable enable
+
+using System;
+using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using AndroidX.Fragment.App;
 using AndroidX.ViewPager2.Adapter;
+using AView = Android.Views.View;
 
 namespace Microsoft.Maui.Controls.Platform
 {
 	internal class MultiPageFragmentStateAdapter<[DynamicallyAccessedMembers(BindableProperty.DeclaringTypeMembers)] T> : FragmentStateAdapter where T : Page
 	{
 		MultiPage<T> _page;
 		readonly IMauiContext _context;
+		List<ItemKey> keys = new List<ItemKey>();
 
 		public MultiPageFragmentStateAdapter(
 			MultiPage<T> page, FragmentManager fragmentManager, IMauiContext context)
@@ -29,20 +36,125 @@ public override Fragment CreateFragment(int position)
 
 		public override long GetItemId(int position)
 		{
-			// https://github.com/dotnet/maui/issues/11529
-			// This should be updated to not use `GetHashCode`
-			return _page.Children[position].GetHashCode();
+			return GetItemIdByPosition(position).ItemId;
 		}
 
 		public override bool ContainsItem(long itemId)
 		{
-			foreach (var item in _page.Children)
+			return GetItemByItemId(itemId) != null;
+		}
+
+		ItemKey GetItemIdByPosition(int position)
+		{
+			CheckItemKeys();
+			var page = _page.Children[position];
+			for (var i = 0; i < keys.Count; i++)
+			{
+				ItemKey item = keys[i];
+				if (item.Page == page)
+				{
+					return item;
+				}
+			}
+
+			ItemKey itemKey = new ItemKey(page, (ik) => keys.Remove(ik));
+			keys.Add(itemKey);
+
+			return itemKey;
+		}
+
+		ItemKey? GetItemByItemId(long itemId)
+		{
+			CheckItemKeys();
+			for (var i = 0; i < keys.Count; i++)
+			{
+				ItemKey item = keys[i];
+				if (item.ItemId == itemId)
+				{
+					return item;
+				}
+			}
+
+			return null;
+		}
+
+		void CheckItemKeys()
+		{
+			for (var i = 0; i < keys.Count; i++)
+			{
+				ItemKey item = keys[i];
+
+				if (!_page.Children.Contains(item.Page))
+				{
+					// Disconnect will remove the ItemKey from the keys list
+					item.Disconnect();
+				}
+			}
+		}
+
+		class ItemKey
+		{
+			Page? _page;
+			Action<ItemKey>? _markInvalid;
+			bool _stableView;
+			object? _platformView;
+
+			public ItemKey(Page page, Action<ItemKey> markInvalid)
+			{
+				_page = page;
+				_markInvalid = markInvalid;
+				_page.HandlerChanging += OnHandlerChanging;
+				_page.HandlerChanged += OnHandlerChanged;
+				ItemId = AView.GenerateViewId();
+			}
+
+			public bool Disconnected => _page != null;
+			public Page? Page => _page;
+			public long ItemId { get; }
+			public void Disconnect()
 			{
-				if (item.GetHashCode() == itemId)
-					return true;
+				if (_page == null)
+					return;
+
+				_markInvalid?.Invoke(this);
+
+				if (_page != null)
+				{
+					_page.HandlerChanging -= OnHandlerChanging;
+					_page.HandlerChanged -= OnHandlerChanged;
+					_page = null;
+				}
+
+				_platformView = null;
+			}
+
+			public void SetToStableView()
+			{
+				_stableView = true;
+			}
+
+			void OnHandlerChanging(object? sender, HandlerChangingEventArgs e)
+			{
+				if (_stableView && _platformView != null)
+					Disconnect();
+			}
+
+			void OnHandlerChanged(object? sender, EventArgs e)
+			{
+				if (_page == null || _platformView != null)
+				{
+					if (sender is Page page)
+						page.HandlerChanged -= OnHandlerChanged;
+
+					return;
+				}
+
+				_platformView = _page.Handler?.PlatformView;
+
+				if (_platformView != null)
+					_page.HandlerChanged -= OnHandlerChanged;
 			}
 
-			return false;
 		}
 	}
 }

src/Controls/src/Core/Platform/Android/TabbedPageManager.cs

@@ -183,7 +183,7 @@ void RemoveTabs()
 						.GetNavigationRootManager()
 						.FragmentManager;
 
-				if (!fragmentManager.IsDestroyed())
+				if (!fragmentManager.IsDestroyed(_context?.Context))
 				{
 					_ = _context
 							.GetNavigationRootManager()

src/Core/src/Handlers/NavigationPage/NavigationViewHandler.Android.cs

@@ -20,6 +20,12 @@ protected override View CreatePlatformView()
 			return view;
 		}
 
+
+		void OnViewChildAdded(object? sender, ViewGroup.ChildViewAddedEventArgs e)
+		{
+			_stackNavigationManager?.CheckForFragmentChange();
+		}
+
 		StackNavigationManager CreateNavigationManager()
 		{
 			_ = MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} should have been set by base class.");
@@ -35,6 +41,9 @@ protected override void ConnectHandler(View platformView)
 
 			platformView.ViewAttachedToWindow += OnViewAttachedToWindow;
 			platformView.ViewDetachedFromWindow += OnViewDetachedFromWindow;
+
+			if (platformView is FragmentContainerView fcw)
+				fcw.ChildViewAdded += OnViewChildAdded;
 		}
 
 		void OnViewDetachedFromWindow(object? sender, View.ViewDetachedFromWindowEventArgs e)
@@ -61,6 +70,9 @@ private protected override void OnDisconnectHandler(View platformView)
 			platformView.ViewDetachedFromWindow -= OnViewDetachedFromWindow;
 			platformView.LayoutChange -= OnLayoutChanged;
 
+			if (platformView is FragmentContainerView fcw)
+				fcw.ChildViewAdded -= OnViewChildAdded;
+
 			_stackNavigationManager?.Disconnect();
 			base.OnDisconnectHandler(platformView);
 		}

src/Core/src/Platform/Android/ContextExtensions.cs

@@ -419,5 +419,36 @@ public static Rect ToCrossPlatformRectInReferenceFrame(this Context context, int
 			return Rect.FromLTRB(0, 0,
 				deviceIndependentRight - deviceIndependentLeft, deviceIndependentBottom - deviceIndependentTop);
 		}
+
+		internal static bool IsDestroyed(this Context? context)
+		{
+			if (context == null)
+				return true;
+
+			if (context.GetActivity() is FragmentActivity fa)
+			{
+				if (fa.IsDisposed())
+					return true;
+
+				var stateCheck = AndroidX.Lifecycle.Lifecycle.State.Destroyed;
+
+				if (stateCheck != null &&
+					fa.Lifecycle.CurrentState == stateCheck)
+				{
+					return true;
+				}
+
+				if (fa.IsDestroyed)
+					return true;
+			}
+
+			return context.IsDisposed();
+		}
+
+		internal static bool IsPlatformContextDestroyed(this IElementHandler? handler)
+		{
+			var context = handler?.MauiContext?.Context;
+			return context.IsDestroyed();
+		}
 	}
 }

src/Core/src/Platform/Android/FragmentManagerExtensions.cs

@@ -1,5 +1,6 @@
 
 using System;
+using Android.Content;
 using AndroidX.Fragment.App;
 
 namespace Microsoft.Maui.Platform
@@ -57,14 +58,20 @@ public static FragmentTransaction BeginTransactionEx(this FragmentManager fragme
 			return fragmentManager.BeginTransaction();
 		}
 
-		public static bool IsDestroyed(this FragmentManager? obj)
+		public static bool IsDestroyed(this FragmentManager? obj, Context? context)
 		{
 			if (obj == null)
 				return true;
 
+			if (context == null)
+				return true;
+
 			if (obj.IsDestroyed)
 				return true;
 
+			if (context.IsDestroyed())
+				return true;
+
 			return obj.IsDisposed();
 		}
 

src/Core/src/Platform/Android/MauiContextExtensions.cs

@@ -79,14 +79,16 @@ internal static View ToPlatform(
 		{
 			if (view.Handler?.MauiContext is MauiContext scopedMauiContext)
 			{
-				// If the incoming mauiContext has the same activity and fragment manager
-				// then we just update the layourInflater for any children that will want to participate
-				// with this inflation flow
+				// If this handler becomes to a different activity then we need to 
+				// recreate the view.
+				// If it's the same activity we just update the layout inflater
+				// and the fragment manager so that the platform view doesn't recreate
+				// underneath the users feet
 				if (scopedMauiContext.GetActivity() == context.GetActivity() &&
-					scopedMauiContext.GetFragmentManager() == childFragmentManager &&
 					view.Handler.PlatformView is View platformView)
 				{
 					scopedMauiContext.AddWeakSpecific(layoutInflater);
+					scopedMauiContext.AddWeakSpecific(childFragmentManager);
 					return platformView;
 				}
 			}

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

@@ -0,0 +1,22 @@
+using Android.OS;
+using Android.Runtime;
+using Android.Views;
+using AndroidX.Navigation;
+using AndroidX.Navigation.Fragment;
+
+namespace Microsoft.Maui.Platform
+{
+	[Register("microsoft.maui.platform.MauiNavHostFragment")]
+	class MauiNavHostFragment : NavHostFragment
+	{
+		public StackNavigationManager? StackNavigationManager { get; set; }
+
+		public MauiNavHostFragment()
+		{
+		}
+
+		protected MauiNavHostFragment(nint javaReference, JniHandleOwnership transfer) : base(javaReference, transfer)
+		{
+		}
+	}
+}

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

@@ -125,7 +125,7 @@ void SetContentView(IView? view)
 		{
 			if (view == null)
 			{
-				if (_viewFragment != null && !FragmentManager.IsDestroyed())
+				if (_viewFragment != null && !FragmentManager.IsDestroyed(_mauiContext.Context))
 				{
 					FragmentManager
 						.BeginTransaction()