[BUG] Crash occurs when a page transition occurs while displaying a Snackbar with an anchor specified on iOS

[cat0363]

Is there an existing issue for this?

• I have searched the existing issues

Did you read the "Reporting a bug" section on Contributing file?

• I have read the "Reporting a bug" section on Contributing file: https://github.com/CommunityToolkit/Maui/blob/main/CONTRIBUTING.md#reporting-a-bug

Current Behavior

The app will crash if a page transition occurs while displaying a Snackbar with an anchor specified.
This issue only occurs on iOS and not on Android.

Expected Behavior

Even if a page transition occurs while displaying a Snackbar with an anchor specified, the app will continue to operate without crashing.

Steps To Reproduce

1. Press the Next Page Button.
2. Press the Show Snackbar Button.
3. Press the Back Pag Button.

Step 3 should be performed while the snack bar displayed in step 2 is displayed.
The application crashes at step 3.

Link to public reproduction project repository

https://github.com/cat0363/MauiComm-IssueSnackbarCrash.git

Environment

- .NET MAUI CommunityToolkit: 12.1.0
- OS: iOS 17.0
- .NET MAUI: 9.0.90

Anything else?

Below is the debug log.

ObjCRuntime.ObjCException: 'Objective-C exception thrown. Name: NSGenericException Reason: Unable to activate constraint with anchors <NSLayoutYAxisAnchor:0x600001778d00 "UILayoutGuide:0x600003b3c8c0'UIViewSafeAreaLayoutGuide'.bottom"> and <NSLayoutYAxisAnchor:0x600001755b00 "UILayoutGuide:0x600003b44c40'UIViewSafeAreaLayoutGuide'.top"> because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That's illegal.
Native stack trace:
0 CoreFoundation 0x000000018048d8a8 __exceptionPreprocess + 172
1 libobjc.A.dylib 0x000000018008409c objc_exception_throw + 56
2 CoreAutoLayout 0x00000001ca3c4430 -[NSLayoutConstraint setActive:] + 0
3 libxamarin-dotnet-debug.dylib 0x00000001038f4ef8 xamarin_dyn_objc_msgSend + 160
4 MauiComm-IssueSnackbarCrash 0x0000000102e7189c interp_to_native_trampoline + 172
5 libmonosgen-2.0.dylib 0x0000000103c49c6c ves_pinvoke_method + 584
6 libmonosgen-2.0.dylib 0x0000000103c3e408 mono_interp_exec_method + 2936
7 libmonosgen-2.0.dylib 0x0000000103c3be60 interp_runtime_invoke + 244
8 libmonosgen-2.0.dylib 0x0000000103b57954 mono_jit_runtime_invoke + 1244
9 libmonosgen-2.0.dylib 0x0000000103d15e40 mono_runtime_invoke_checked + 148
10 libmonosgen-2.0.dylib 0x0000000103d19a18 mono_runtime_invoke + 540
11 libxamarin-dotnet-debug.dylib 0x00000001038ec0a0 xamarin_invoke_trampoline + 5424
12 libxamarin-dotnet-debug.dylib 0x00000001038f3bd0 xamarin_arch_trampoline + 148
13 libxamarin-dotnet-debug.dylib 0x00000001038f4dcc xamarin_arm64_common_trampoline + 64
14 UIKitCore 0x00000001857cdb1c -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1492
15 QuartzCore 0x0000000189f6fdd4 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 440
16 QuartzCore 0x0000000189f7ab30 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 124
17 QuartzCore 0x0000000189e963bc _ZN2CA7Context18commit_transactionEPNS_11TransactionEdPd + 460
18 QuartzCore 0x0000000189ec5bf0 _ZN2CA11Transaction6commitEv + 652
19 QuartzCore 0x0000000189ec70a4 _ZN2CA11Transaction25flush_as_runloop_observerEb + 68
20 CoreFoundation 0x00000001803ed648 CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION + 32
21 CoreFoundation 0x00000001803e804c __CFRunLoopDoObservers + 528
22 CoreFoundation 0x00000001803e8504 __CFRunLoopRun + 968
23 CoreFoundation 0x00000001803e7d28 CFRunLoopRunSpecific + 572
24 GraphicsServices 0x000000018e7cdbc0 GSEventRunModal + 160
25 UIKitCore 0x00000001852bafdc -[UIApplication _run] + 868
26 UIKitCore 0x00000001852bec54 UIApplicationMain + 124
27 libxamarin-dotnet-debug.dylib 0x00000001038a5a94 xamarin_UIApplicationMain + 60
28 libmonosgen-2.0.dylib 0x0000000103c4b3b0 do_icall + 316
29 libmonosgen-2.0.dylib 0x0000000103c498d4 do_icall_wrapper + 356
30 libmonosgen-2.0.dylib 0x0000000103c3e228 mono_interp_exec_method + 2456
31 libmonosgen-2.0.dylib 0x0000000103c3be60 interp_runtime_invoke + 244
32 libmonosgen-2.0.dylib 0x0000000103b57954 mono_jit_runtime_invoke + 1244
33 libmonosgen-2.0.dylib 0x0000000103d15e40 mono_runtime_invoke_checked + 148
34 libmonosgen-2.0.dylib 0x0000000103d1d0a0 mono_runtime_exec_main_checked + 116
35 libmonosgen-2.0.dylib 0x0000000103baaa40 mono_jit_exec + 364
36 libxamarin-dotnet-debug.dylib 0x00000001038f3a6c xamarin_main + 2028
37 MauiComm-IssueSnackbarCrash 0x0000000102e890d0 main + 64
38 dyld 0x0000000103109558 start_sim + 20
39 ??? 0x0000000102ed2274 0x0 + 4344062580

[cat0363]

The only workaround is to keep an instance of Snackbar around and call the Dismiss method in the OnNavigatingFrom event.

    private ISnackbar snackbar;

    private void btnShow_Clicked(object sender, EventArgs e)
    {
        snackbar = Snackbar.Make("This is test message.", null, string.Empty, new TimeSpan(0, 0, 0, 0, 3000), new CommunityToolkit.Maui.Core.SnackbarOptions() { BackgroundColor = Colors.Green, TextColor = Colors.White }, gdSnackBarAnchor);
        snackbar.Show();
    }

    private void btnBack_Clicked(object sender, EventArgs e)
    {
        Shell.Current.Navigation.PopAsync(false);
    }

    protected async override void OnNavigatingFrom(NavigatingFromEventArgs args)
    {
        if (snackbar is not null)
        {
            await snackbar.Dismiss();
        }
        base.OnNavigatingFrom(args);
    }

At the very least, any currently displayed Snackbars will be forcibly closed, but this will prevent the app from crashing when switching between screens.