Description

When navigating back from a page to the previous page (A) and this page is then navigating forward to another page inside the Shell OnNavigated event, the Handler for the page A will be null. This leads to the next navigation crashing the app under iOS with the following exception:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.ElementForViewController(UIViewController viewController)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.NavDelegate.WillShowViewController(UINavigationController navigationController, UIViewController viewController, Boolean animated)
--- End of stack trace from previous location ---
   at ObjCRuntime.Runtime.ThrowException(IntPtr gchandle)
   at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName)
   at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass)
   at MauiIosNavigationCrashes.Program.Main(String[] args)

This happened after upgrading to .NET 9 with MAUI 9.x.x.
Using .NET 8 and MAUI 8.0.100 this crash does not happen.

There are similar issues already present but they were closed due to inactivity and did not provide a way of reproduction:

• MAUI IOS System.NullReferenceException: Arg_NullReferenceException #30563
• Maui IOS System.NullReferenceException - Arg_NullReferenceException #29294

Steps to Reproduce

1. Clone the reproduction repository
2. Start the application on iOS
3. Click on "Open Page1"
4. Click on "OpenModalPage"
5. Click on "Close Modal"
6. (On Page2) Click on "Navigate to next page"

Actual result:
The app crashes with the exception mentioned above.

Expected result:
The app does not crash.

Link to public reproduction project repository

https://github.com/FinnKr/MauiIosNavigationCrashes

Version with bug

9.0.110 SR11

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

.NET 8 (MAUI 8.0.100)

Affected platforms

iOS

Affected platform versions

Tested with iOS 18.5 & iOS 26.0

Did you find any workaround?

Edit: The second workaround below is cleaner in my opinion

In our actual use case we could remove the page with a Handler=null from the NavigationStack before navigating. This is only possible because the user is not able to navigate back again after this page.

So under those circumstances a workaround is this:

var pageToRemove = Shell.Current.Navigation.NavigationStack.FirstOrDefault(page => page is { Handler: null });
if (pageToRemove != null)
{
    Shell.Current.Navigation.RemovePage(pageToRemove);
}

// Navigate here

Another workaround I found was to move the navigation to the MainThread/Dispatcher:

Application.Current!.Dispatcher.Dispatch(() =>
{
    // Navigate here
});

Relevant log output

See exception above