Workaround WinUI bug with adding/removing flyouts

src/Controls/samples/Controls.Sample/Pages/Core/ContextFlyoutPage.xaml

@@ -30,9 +30,11 @@
                 <FlyoutBase.ContextFlyout>
                     <MenuFlyout>
                         <MenuFlyoutItem Text="Add top-level menu items" Clicked="OnAddMenuClicked"></MenuFlyoutItem>
-                        <MenuFlyoutSubItem Text="Sub menu items go in here">
+                        <MenuFlyoutSubItem Text="Sub menu items go in here" x:Name="subMenu">
                             <MenuFlyoutItem Text="Add sub menu items below here" Clicked="OnAddSubMenuClicked"></MenuFlyoutItem>
                             <MenuFlyoutSeparator />
+                            <MenuFlyoutSeparator />
+                            <MenuFlyoutItem Text="Remove sub menu item above here" Clicked="OnRemoveSubMenuClicked" x:Name="removeSubMenuItems" IsEnabled="False"></MenuFlyoutItem>
                         </MenuFlyoutSubItem>
                     </MenuFlyout>
                 </FlyoutBase.ContextFlyout>

src/Controls/samples/Controls.Sample/Pages/Core/ContextFlyoutPage.xaml.cs

@@ -150,18 +150,48 @@ void OnAddMenuClicked(object sender, EventArgs e)
 		void OnAddSubMenuClicked(object sender, EventArgs e)
 		{
 			var subMenu = (MenuFlyoutSubItem)((MenuFlyoutItem)sender).Parent;
-			AddNewMenu(subMenu, "sub-menu");
+			AddNewMenu(subMenu, "sub-menu", subMenu.Count - 2, subMenu.Count % 2 == 0);
+			CheckSubMenu();
+		}
+		void OnRemoveSubMenuClicked(object sender, EventArgs e)
+		{
+			var subMenu = (MenuFlyoutSubItem)((MenuFlyoutItem)sender).Parent;
+			subMenu.RemoveAt(subMenu.Count - 3);
+			CheckSubMenu();
 		}
 
-		private void AddNewMenu(IList<IMenuElement> parent, string newItemType)
+		void CheckSubMenu()
+		{
+			removeSubMenuItems.IsEnabled = subMenu.Count > 4;
+		}
+
+		private void AddNewMenu(IList<IMenuElement> parent, string newItemType, int index = -1, bool subMenuItem = false)
 		{
 			var newItemLocalValue = newMenuItemCount;
-			var newMenuItem = new MenuFlyoutItem() { Text = $"New {newItemType} menu item #{newItemLocalValue}" };
-			newMenuItem.Clicked += (s, e) => DisplayAlert(
+			IMenuElement newMenuItem;
+			MenuFlyoutItem mfi = new MenuFlyoutItem() { Text = $"New {newItemType} menu item #{newItemLocalValue}" };
+
+			mfi.Clicked += (s, e) => DisplayAlert(
 				title: "New Menu Item Click",
 				message: $"The new menu item {newItemLocalValue} was clicked",
 				cancel: "OK");
-			parent.Add(newMenuItem);
+
+			if (!subMenuItem)
+			{
+				newMenuItem = mfi;
+			}
+			else
+			{
+				var subItem = new MenuFlyoutSubItem() { Text = $"New {newItemType} menu item #{newItemLocalValue}" };
+				newMenuItem = subItem;
+				subItem.Add(mfi);
+			}
+
+			if (index == -1)
+				parent.Add(newMenuItem);
+			else
+				parent.Insert(index, newMenuItem);
+
 			newMenuItemCount++;
 		}
 	}

src/Core/src/Handlers/MenuFlyoutHandler/MenuFlyoutHandler.Windows.cs

@@ -9,6 +9,19 @@ protected override MenuFlyout CreatePlatformElement()
 			return new MenuFlyout();
 		}
 
+		protected override void DisconnectHandler(MenuFlyout platformView)
+		{
+			if (VirtualView is not null)
+			{
+				foreach (var item in VirtualView)
+				{
+					item.Handler?.DisconnectHandler();
+				}
+			}
+
+			base.DisconnectHandler(platformView);
+		}
+
 		public override void SetVirtualView(IElement view)
 		{
 			base.SetVirtualView(view);

src/Core/src/Handlers/MenuFlyoutSubItem/MenuFlyoutSubItemHandler.Windows.cs

@@ -15,6 +15,14 @@ protected override MenuFlyoutSubItem CreatePlatformElement()
 
 		protected override void DisconnectHandler(MenuFlyoutSubItem PlatformView)
 		{
+			if (VirtualView is not null)
+			{
+				foreach (var item in VirtualView)
+				{
+					item.Handler?.DisconnectHandler();
+				}
+			}
+
 			base.DisconnectHandler(PlatformView);
 			PlatformView.Tapped -= OnTapped;
 		}
@@ -47,33 +55,66 @@ public static void MapSource(IMenuFlyoutSubItemHandler handler, IMenuFlyoutSubIt
 		public override void SetVirtualView(IElement view)
 		{
 			base.SetVirtualView(view);
-			Clear();
+			PlatformView.Items.Clear();
 
 			foreach (var item in ((IMenuFlyoutSubItem)view))
 			{
-				Add(item);
+				PlatformView.Items.Add((MenuFlyoutItemBase)item.ToPlatform(MauiContext!));
 			}
 		}
 
-		public void Add(IMenuElement view)
+		// workaround WinUI bug https://github.com/microsoft/microsoft-ui-xaml/issues/7797
+		void Reset()
 		{
-			PlatformView.Items.Add((MenuFlyoutItemBase)view.ToPlatform(MauiContext!));
-		}
+			if (VirtualView.Parent?.Handler is IElementHandler pvh)
+			{
+				var vv = VirtualView;
+				IList<MenuFlyoutItemBase>? items = null;
+				if (pvh.PlatformView is MenuFlyout mf)
+				{
+					items = mf.Items;
 
-		public void Remove(IMenuElement view)
-		{
-			if (view.Handler != null)
-				PlatformView.Items.Remove((MenuFlyoutItemBase)view.ToPlatform());
-		}
+				}
+				else if (pvh.PlatformView is MenuFlyoutSubItem mfsi)
+				{
+					items = mfsi.Items;
+				}
 
-		public void Clear()
-		{
-			PlatformView.Items.Clear();
-		}
+				if (items is not null)
+				{
+					var index = items.IndexOf(PlatformView);
 
-		public void Insert(int index, IMenuElement view)
-		{
-			PlatformView.Items.Insert(index, (MenuFlyoutItemBase)view.ToPlatform(MauiContext!));
+					if (index < 0)
+						return;
+
+					items.RemoveAt(index);
+
+					// You have to create the entire menu whenever adding/removing items.
+					// I tried to just remove and re-add this one item from the parent but that doesn't work.
+					// Also, if you try to reuse any MenuFlyoutItems on the new control it crashes.
+					//
+					// The following code crashes with a catastrophic failure.
+					//
+					// oldMenu.Items.Remove(item);					
+					// newMenu.Items.Add(item); 
+					// You have to create a new MenuFlyoutSubMenuItem and all of the children
+
+					vv.Handler?.DisconnectHandler();
+					items.Insert(index, (MenuFlyoutItemBase)vv.ToPlatform(MauiContext!));
+				}
+			}
 		}
+
+		public void Add(IMenuElement view) =>
+			Reset();
+
+		public void Remove(IMenuElement view) =>
+			Reset();
+
+		public void Clear() =>
+			Reset();
+
+		public void Insert(int index, IMenuElement view) =>
+			Reset();
 	}
 }

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

@@ -14,6 +14,7 @@ Microsoft.Maui.Layouts.FlexBasis.Equals(Microsoft.Maui.Layouts.FlexBasis other)
 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.Handlers.MenuFlyoutHandler.DisconnectHandler(Microsoft.UI.Xaml.Controls.MenuFlyout! 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