[Bug] NullReferenceException when displaying Toast or SnackBar

[maxkoshevoi]

Description

It's a bit tricky to reproduce, but I think it happens when you display toast and change page at the same time.

Here's how ViewModel displays the toast:

await Shell.Current?.CurrentPage?.DisplayToastAsync(LN.AutoupdateFailed);

And here's exception stack:

Xamarin.CommunityToolkit.UI.Views SnackBar.Show (Xamarin.Forms.Page sender, Xamarin.CommunityToolkit.UI.Views.Options.SnackBarOptions arguments)
Xamarin.CommunityToolkit.Extensions PageExtension.DisplayToastAsync (Xamarin.Forms.Page page, System.String message, System.Int32 durationMilliseconds)

Shell.Current.CurrentPage is not null before (since method gets called) and after (checked in catch block) DisplayToastAsync execution.

Update: It crashes on this line:

Steps to Reproduce

1. Create Shell app with TabbBar and two tabs
2. Create button on one of the tabs that executes this code:

await Shell.Current.GoToAsync("RouteToOtherTab");
try
{
    await Shell.Current.CurrentPage.DisplayToastAsync("");
}
catch (Exception ex)
{
    await Shell.Current.CurrentPage.DisplayAlert("Error", ex.ToString(), "Ok");
}

3. Press the button

Expected Behavior

Displaying toast or snackbar doesn't throw exception

Actual Behavior

Displaying toast or snackbar throws exception

Basic Information

• Version with issue: 1.0.3
• Last known good version: -
• IDE:
• Platform Target Frameworks:
  • iOS:
  • Android: 11
  • UWP:
• Android Support Library Version:
• Nuget Packages:
• Affected Devices:

Workaround

Wrap every DisplayToastAsync and DisplaySnackBarAsync in try-catch

Reproduction imagery

Reproduction Link

App7.zip

[maxkoshevoi]

@pictos

• Created app that reproduces the error (zip is in the issue description)
• This appears to be shell only and when switching between tabs. Tested it with Navigation.PopAsync, issue didn't happen.

[pictos]

Looks like that's a Shell issue because the GoToAsync returns but the Page Renderer isn't created yet. So the issue isn't with our code and with Shell navigation, I suppose.
When I add that Task.Delay everything works as expected. I saw that before in some Shell Navigation areas. I'm very tempted to close this issue, but first I would like to have a @PureWeen input here.

 private async Task Button_Clicked()
        {
            await Shell.Current.GoToAsync("//tabbar/About");
			try
			{
				await Task.Delay(10);
				await Shell.Current.CurrentPage.DisplayToastAsync(string.Empty);
			}
			catch (Exception ex)
			{
				await Shell.Current.CurrentPage.DisplayAlert("Error", ex.ToString(), "Ok");
			}
		}