Maui Shell ios crashes on navigation

[PureWeen]

Description

https://developercommunity.visualstudio.com/t/Maui-Shell-ios-crashes-on-navigation/10441135

I am intermittantly getting a null reference exception in Main when navigating in a Maui Shell iOS app. To be honest, I have not tried to reproduce this in Android, so I don’t know if it happens there.

Anyways, this seems to happen when you have multiple pages in a chain. Page A => Tab Page => Page B => Page C => Page D => Back to Page A.

I’ve seen it blow up on pages D and A. In my production app, there is only one page it’s blowing up on, but it does it pretty consistently.

This issue has been reported a few times before, but has always been closed because it can’t be reproduced. I’m adding a link to a sample project, screenshots, and logs. The sample project has produced the error, but you may have to go through the sequence (just click the buttons) many times. I’ve had it happen on the first try and I’ve not had it happen until the 20th try.

When it happens, it will dump you to Program.cs in UIApplication.Main with a null reference exception. You can’t catch it anywhere except for Program.cs, because it happens inside the inner workings. The screenshots are in the shared files.

This is a very critical bug. It is unpredicatable and it completely crashes the app. At this point, I have a page that crashes 3 out of every 4 times.

You can get to the sample project and supporting files at this link.

https://1drv.ms/f/s!AhJ6I4T65XJfgu4_8FhpL26cUoNQhA?e=QO6DBy

EDIT:

This may be my issue. I noticed on one of my web searches that there was a permanent issue with navigation after trying to call navigation off the main thread (#13538). That had me go look at my code, and I realized I’m not actually calling it on the main thread. I made the change in my sample project (uploaded the modified ViewModel.cs, but didn’t change the uploaded project) and tried to get it to happen. It didn’t.

I can’t try it in my main project right this second, but I will later to see if that resolves the issue. Even if it does, a better error message - like the one you normally get when you execute on the wrong thread - would be amazing. It’s also very odd that I’ve spent hundreds of hours working in this app and have never had a null reference crash happen on navigation.

At any rate, I’ll give it a try in my main app and report back.

EDIT #2

That wasn’t the problem. I did make that change, but I’m still getting the same error on my main application. I stepped through the code and verified that I am on the main thread. I included another screenshot that shows in the logic that I’m in the main thread.

I was also able to reproduce it again in the sample application. It took me about 20 times of doing it, but it does still happen.

[samhouts]

Same as #16862?

Edit: yes, yes it is. 🤦‍♀️I meant #16860.

[DDHSchmidt]

Sounds eerily familiar

EDIT:
After following the link to the project in OneDrive it turns out that it is actually a .Net 7 project while my problem pertains to the latest preview of .Net 8

We've added this issue to our backlog, and we will work to address it as time and resources allow. If you have any additional information or questions about this issue, please leave a comment. For additional info about issue management, please read our Triage Process.

[Juansero29]

Hhmm.. My issue was pointed here. But seems like there's still no resolution. Is there any updates on where is this going or when will it be solved?

[PureWeen]

Hhmm.. My issue was pointed here. But seems like there's still no resolution. Is there any updates on where is this going or when will it be solved?

can you attach a repro and a stack trace?

[Juansero29]

@PureWeen a stack trace can be found at #17034

No repro yet however, haven't got the time to produce a separate project for this as of now. I'll give it a try this weekend. Seems to me that it's only ocurring when calling Shell.Current.GoToAsync from the code. So a mild-complex app needs to be created, not just with tabbar navigation like the current MAUI sample. I'll try to produce a repro repository as soon as I can.

[PureWeen]

@PureWeen a stack trace can be found at #17034

No repro yet however, haven't got the time to produce a separate project for this as of now. I'll give it a try this weekend. Seems to me that it's only ocurring when calling Shell.Current.GoToAsync from the code. So a mild-complex app needs to be created, not just with tabbar navigation like the current MAUI sample. I'll try to produce a repro repository as soon as I can.

If you call this code from the UIThread you get a crash?

at Nou.ViewModels.ShellPageViewModel.Load(Object parameter) in /Users/juansero29/Projects/Nou/Nou/ViewModels/ShellPageViewModel.cs:line 124\n

[Juansero29]

@PureWeen I could repro in a a project that you can fully access. In this state, the app will crash in iOS but not on Android.

Take special care to look at the method Load inside AppShellVM. You can put a breakpoint in line 50, to check that app goes to there, and then crashes when executing line 53.

Also note that I am opening and executing this project from a M1 Macbook Pro in Visual Studio for Mac. Haven't tried it on a windows machine to check if behavior is different, but I guess it shouldn't be different.

[seemeest]

Hello, I had a similar problem with Maui.Net 8, I was able to solve it by adding builder.Services.AddTransient<[error page]>();

[seemeest]

hello, I was able to solve this problem by adding

    private async  void Chat_Tapped(object sender, TappedEventArgs e)
    {
        var stack = Shell.Current.Navigation.NavigationStack.ToArray();
        for (int i = stack.Length - 1; i > 0; i--)
        {
            Shell.Current.Navigation.RemovePage(stack[i]);
        }
        //Singleton Page
        await Shell.Current.GoToAsync(nameof(AllChats), false);
    }