[iOS] Fix App crash with NullReferenceException in ShellSectionRenderer

src/Controls/src/Core/Page/Page.cs

@@ -852,6 +852,24 @@ internal void SendNavigatedFrom(NavigatedFromEventArgs args, bool disconnectHand
 			if (args.NavigationType == NavigationType.Pop ||
 				args.NavigationType == NavigationType.PopToRoot)
 			{
+#if IOS
+				// Don't dispose Handlers too early on iOS!
+				// iOS aggressively cleans up page Handlers during navigation, but if the page
+				// is still in Shell's navigation stack, users can navigate back to it.
+				// Disposing the Handler makes the page invisible.
+				// So only dispose Handler if page not in current Shell stack
+				if (Shell.Current != null)
+				{
+					// Check if this page is still referenced in Shell's navigation stack
+					var currentStack = Shell.Current.CurrentItem?.CurrentItem?.Stack;
+					if (currentStack?.Contains(this) == true)
+					{
+						// Page is still in navigation stack, don't dispose Handler
+						return;
+					}
+				}
+#endif
+
 				if (!this.IsLoaded)
 				{
 					this.DisconnectHandlers();

src/Controls/tests/TestCases.HostApp/Issues/Issue31961.cs

@@ -0,0 +1,194 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+// Interface for navigation awareness
+public interface INavigationAware
+{
+    void OnShellNavigated(ShellNavigatedEventArgs args);
+}
+
+[Issue(IssueTracker.Github, 31961, "[iOS] App crash with NullReferenceException in ShellSectionRenderer", PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue31961 : Shell
+{
+	public Issue31961()
+	{
+		var mainPage = new ShellContent
+		{
+			Title = "Main",
+			Content = new Issue31961MainPage(),
+			Route = "MainPage"
+		};
+
+		var tabBar = new TabBar();
+		tabBar.Items.Add(mainPage);
+		Items.Add(tabBar);
+
+		// Register routes for navigation
+		Routing.RegisterRoute("Issue31961FirstPage", typeof(Issue31961FirstPage));
+		Routing.RegisterRoute("Issue31961SecondPage", typeof(Issue31961SecondPage));
+		Routing.RegisterRoute("Issue31961ThirdPage", typeof(Issue31961ThirdPage));
+		Routing.RegisterRoute("Issue31961ModalPage", typeof(Issue31961ModalPage));
+	}
+
+	protected override void OnNavigated(ShellNavigatedEventArgs args)
+	{
+		if (Current.CurrentPage?.BindingContext is INavigationAware bindingContext)
+		{
+			bindingContext.OnShellNavigated(args);
+		}
+
+		base.OnNavigated(args);
+	}
+}
+
+public partial class Issue31961MainPage : ContentPage
+{
+	public Command NavigateToPage1Command { get; }
+
+	public Issue31961MainPage()
+	{
+		// Initialize command
+		NavigateToPage1Command = new Command(async () => await NavigateToPage1Async());
+
+		var btnNavigate = new Button
+		{
+			Text = "Go to Page 1",
+			FontSize = 20,
+			AutomationId = "MainPage",
+			HorizontalOptions = LayoutOptions.Center,
+			VerticalOptions = LayoutOptions.Center,
+			Command = NavigateToPage1Command
+		};
+
+		Content = btnNavigate;
+	}
+
+	async Task NavigateToPage1Async()
+	{
+		await Shell.Current.GoToAsync("Issue31961FirstPage");
+	}
+}
+
+public class Issue31961FirstPage : ContentPage, INavigationAware
+{
+	bool _wasModalShown = false;
+
+	public Command OpenModalCommand { get; }
+	public Command NavigateToPage2Command { get; }
+
+	public Issue31961FirstPage()
+	{
+		Title = "Page 1";
+		BindingContext = this; // Set binding context to enable INavigationAware
+
+		// Initialize commands
+		OpenModalCommand = new Command(async () => await OpenModalAsync());
+		NavigateToPage2Command = new Command(async () => await NavigateToPage2Async());
+
+		var btnOpenModal = new Button { Text = "Open Modal Page", AutomationId = "OpenModalButton", Command = OpenModalCommand };
+		var btnGoToPage2 = new Button { Text = "Go to Page 2", Command = NavigateToPage2Command };
+
+		Content = new VerticalStackLayout
+		{
+			Padding = 20,
+			Spacing = 20,
+			Children = { btnOpenModal, btnGoToPage2 }
+		};
+	}
+
+	async Task OpenModalAsync()
+	{
+		_wasModalShown = true;
+		await Shell.Current.GoToAsync("Issue31961ModalPage");
+	}
+
+	async Task NavigateToPage2Async()
+	{
+		await Shell.Current.GoToAsync("Issue31961SecondPage");
+	}
+
+	public void OnShellNavigated(ShellNavigatedEventArgs args)
+	{
+		// This will be called when Shell navigation occurs
+		if (_wasModalShown)
+		{
+			_wasModalShown = false; // Reset the flag
+			// Navigate to Page2 only after modal action is completed
+			NavigateToPage2Command.Execute(null);
+		}
+	}
+}
+
+public class Issue31961ModalPage : ContentPage
+{
+	public Command CloseModalCommand { get; }
+
+	public Issue31961ModalPage()
+	{
+		Title = "Modal Page";
+		BackgroundColor = Colors.LightGray;
+
+		// Initialize command
+		CloseModalCommand = new Command(async () => await CloseModalAsync());
+
+		var btnClose = new Button { Text = "Close Modal Page", AutomationId = "CloseModalButton", Command = CloseModalCommand };
+
+		Content = new VerticalStackLayout
+		{
+			Padding = 20,
+			Spacing = 20,
+			Children = { new Label { Text = "This is a Modal Page" }, btnClose }
+		};
+	}
+
+	async Task CloseModalAsync()
+	{
+		await Shell.Current.GoToAsync("..");
+	}
+}
+
+public class Issue31961SecondPage : ContentPage
+{
+	public Command NavigateToPage3Command { get; }
+
+	public Issue31961SecondPage()
+	{
+		Title = "Page 2";
+
+		// Initialize command
+		NavigateToPage3Command = new Command(async () => await NavigateToPage3Async());
+
+		var btnGoToPage3 = new Button { Text = "Go to Page 3", AutomationId = "Page2" , Command = NavigateToPage3Command };
+
+		Content = new VerticalStackLayout
+		{
+			Padding = 20,
+			Spacing = 20,
+			Children = { btnGoToPage3 }
+		};
+	}
+
+	async Task NavigateToPage3Async()
+	{
+		await Shell.Current.GoToAsync("Issue31961ThirdPage");
+	}
+}
+
+public class Issue31961ThirdPage : ContentPage
+{
+	public Issue31961ThirdPage()
+	{
+		Title = "Page 3";
+
+		var label = new Label
+		{
+			Text = "Welcome to Page 3",
+			AutomationId = "Page3",
+			HorizontalOptions = LayoutOptions.Center,
+			VerticalOptions = LayoutOptions.Center
+		};
+
+		Content = label;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31961.cs

@@ -0,0 +1,27 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue31961 : _IssuesUITest
+	{
+		public Issue31961(TestDevice device) : base(device) { }
+
+		public override string Issue => "[iOS] App crash with NullReferenceException in ShellSectionRenderer";
+		[Test]
+		[Category(UITestCategories.Shell)]
+		public void VerifyShellNavigationWithModalNavigation()
+		{
+			App.WaitForElement("MainPage");
+			App.Tap("MainPage");
+			App.WaitForElement("OpenModalButton"); 
+			App.Tap("OpenModalButton");
+			App.WaitForElement("CloseModalButton"); 
+			App.Tap("CloseModalButton");
+			App.WaitForElement("Page2");
+			App.Tap("Page2");
+			App.WaitForElement("Page3");
+		}
+	}
+}