Wait for root page to load before processing modal (#15037)

* Wait for root page to load before processing modal

* Update ModalTests.iOS.cs

src/Controls/src/Core/Platform/ModalNavigationManager/ModalNavigationManager.cs

@@ -324,7 +324,7 @@ void ClearModalPages(bool xplat = false, bool platform = false)
 
 		// Windows and Android have basically the same requirement that
 		// we need to wait for the current page to finish loading before
-		// satsifying Modal requests.
+		// satisfying Modal requests.
 		// This will most likely change once we switch Android to using dialog fragments		
 #if WINDOWS || ANDROID
 		IDisposable? _platformPageWatchingForLoaded;
@@ -338,22 +338,33 @@ async Task SyncModalStackWhenPlatformIsReadyAsync()
 				await SyncPlatformModalStackAsync().ConfigureAwait(false);
 			}
 			else if (_window.IsActivated &&
-				_window?.Page?.Handler is not null)
+					_window?.Page?.Handler is not null)
 			{
 				if (CurrentPlatformPage.Handler is null)
 				{
 					CurrentPlatformPage.HandlerChanged += OnCurrentPlatformPageHandlerChanged;
-					;
+
 					_platformPageWatchingForLoaded = new ActionDisposable(() =>
 					{
 						CurrentPlatformPage.HandlerChanged -= OnCurrentPlatformPageHandlerChanged;
 					});
 				}
+				// This accounts for cases where we swap the root page out
+				// We want to wait for that to finish loading before processing any modal changes
+#if ANDROID
+				else if (!_window.Page.IsLoadedOnPlatform())
+				{
+					var windowPage = _window.Page;
+					_platformPageWatchingForLoaded =
+						windowPage.OnLoaded(() => OnCurrentPlatformPageLoaded(windowPage, EventArgs.Empty));
+				}
+#endif
 				else if (!CurrentPlatformPage.IsLoadedOnPlatform() &&
-					CurrentPlatformPage.Handler is not null)
+						  CurrentPlatformPage.Handler is not null)
 				{
+					var currentPlatformPage = CurrentPlatformPage;
 					_platformPageWatchingForLoaded =
-						CurrentPlatformPage.OnLoaded(() => OnCurrentPlatformPageLoaded(_platformPageWatchingForLoaded, EventArgs.Empty));
+						currentPlatformPage.OnLoaded(() => OnCurrentPlatformPageLoaded(currentPlatformPage, EventArgs.Empty));
 				}
 			}
 		}
@@ -382,6 +393,7 @@ bool IsModalPlatformReady
 				bool result =
 					_window?.Page?.Handler is not null &&
 					_window.IsActivated
+					&& _window.Page.IsLoadedOnPlatform()
 					&& CurrentPlatformPage?.Handler is not null
 					&& CurrentPlatformPage.IsLoadedOnPlatform();
 

src/Controls/tests/DeviceTests/Elements/Modal/ModalTests.cs

@@ -5,6 +5,7 @@
 using System.Threading.Tasks;
 using Microsoft.Maui.Controls;
 using Microsoft.Maui.Controls.Handlers;
+using Microsoft.Maui.Controls.Platform;
 using Microsoft.Maui.DeviceTests.Stubs;
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Hosting;
@@ -447,6 +448,23 @@ await CreateHandlerAndAddToWindow<IWindowHandler>(window, async (handler) =>
 
 		}
 
+		[Theory]
+		[ClassData(typeof(PageTypes))]
+		public async Task SwappingRootPageWhileModalPageIsOpenDoesntCrash(Page rootPage, Page newRootPage)
+		{
+			SetupBuilder();
+
+			await CreateHandlerAndAddToWindow<IWindowHandler>(rootPage,
+				async (_) =>
+				{
+					var modalPage = new NavigationPage(new ContentPage());
+					await rootPage.Navigation.PushModalAsync(modalPage);
+					await OnLoadedAsync(modalPage);
+					rootPage.Window.Page = newRootPage;
+					await OnLoadedAsync(newRootPage);
+				});
+		}
+
 		[Theory]
 		[ClassData(typeof(PageTypes))]
 		public async Task BasicPushAndPop(Page rootPage, Page modalPage)
@@ -456,7 +474,8 @@ public async Task BasicPushAndPop(Page rootPage, Page modalPage)
 			await CreateHandlerAndAddToWindow<IWindowHandler>(rootPage,
 				async (_) =>
 				{
-					var currentPage = (rootPage as IPageContainer<Page>).CurrentPage;
+					var currentPage = rootPage.GetCurrentPage();
+
 					await currentPage.Navigation.PushModalAsync(modalPage);
 					await OnLoadedAsync(modalPage);
 					Assert.Equal(1, currentPage.Navigation.ModalStack.Count);
@@ -465,21 +484,27 @@ await CreateHandlerAndAddToWindow<IWindowHandler>(rootPage,
 				});
 
 
-			Assert.Equal(0, (rootPage as IPageContainer<Page>).CurrentPage.Navigation.ModalStack.Count);
+			Assert.Equal(0, rootPage.GetCurrentPage().Navigation.ModalStack.Count);
 		}
 
 		class PageTypes : IEnumerable<object[]>
 		{
 			public IEnumerator<object[]> GetEnumerator()
 			{
-				for (int i = 0; i < 2; i++)
+				for (int i = 0; i < 3; i++)
 				{
 					Func<Page> rootPage;
 
 					if (i == 0)
 						rootPage = () => new NavigationPage(new ContentPage());
-					else
+					else if (i == 1)
 						rootPage = () => new Shell() { CurrentItem = new ContentPage() };
+					else
+						rootPage = () => new FlyoutPage()
+						{
+							Flyout = new ContentPage() { Title = "Flyout" },
+							Detail = new NavigationPage(new ContentPage()) { Title = "Detail" },
+						};
 
 					yield return new object[] {
 						rootPage(), new NavigationPage(new ContentPage())

src/Controls/tests/DeviceTests/Elements/Modal/ModalTests.iOS.cs

@@ -1,5 +1,6 @@
 using System.Threading.Tasks;
 using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Platform;
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Handlers;
 using UIKit;
@@ -23,7 +24,7 @@ public async Task PushModalUsingTransparencies(Page rootPage, Page modalPage)
 			await CreateHandlerAndAddToWindow<IWindowHandler>(rootPage,
 				async (handler) =>
 				{
-					var currentPage = (rootPage as IPageContainer<Page>).CurrentPage;
+					var currentPage = rootPage.GetCurrentPage();
 					await currentPage.Navigation.PushModalAsync(modalPage);
 					await OnLoadedAsync(modalPage);
 					Assert.Equal(1, currentPage.Navigation.ModalStack.Count);
@@ -37,4 +38,4 @@ await CreateHandlerAndAddToWindow<IWindowHandler>(rootPage,
 				});
 		}
 	}
-}
+}