[Bug] FilePicker.PickAsync() returns random results

[formerlymisterhenson]

Description

Whilst I was using FilePicker.PickAsync() in <= 1.7.0 with no problems, our users reported in our current (Xamarin Forms) app release, that the FilePicker is not working anymore (for us). I was able to reproduce that, without Exceptions or permission problems. The problem is, that in about 4 of 5 cases PickAsync returns null instead of the file result.

Well, there are not that many things where you could go wrong, I guess:

try
{
   //Device.BeginInvokeOnMainThread(async () => // did not matter here
   {
       var result = await FilePicker.PickAsync();

       if (result != null) // only 1 in 5 cases
       {
           using var stream = await result.OpenReadAsync();
           ...
       }
   } 
   //);
}
catch (Exception e)
{
   // does not happen
   Log.Error($"blah {e}");
}

I was trying to understand what's the problem here and had a look at: https://github.com/xamarin/Essentials/blob/main/Xamarin.Essentials/FilePicker/FilePicker.ios.cs

I think there is something suspicious about that DismissHandler thing introduced with https://github.com/xamarin/Essentials/pull/1846

documentPicker.PresentationController.Delegate = new Platform.UIPresentationControllerDelegate
{
    DismissHandler = () => GetFileResults(null, tcs)
};

So I reverted Essentials to 1.7.0 and it did work fine again. Upgrading to 1.7.1, 1.7.2, 1.7.3 it does not work (reproducible for me).

Steps to Reproduce (I guess)

1. use FilePicker.PickAsync() on iOS
2. pick a file by tapping one
3. (dialog closes)

Expected Behavior

PickAsync returns a FileResult.

Actual Behavior

PickAsync returns in most cases null.

Basic Information

• Version with issue: 1.7.1, 1.7.2, 1.7.3
• Last known good version: 1.7.0
• IDE: VS 17.3 Pre 1.1
• Platform Target Frameworks:
  • iOS: 15.5 (physical device iPad Pro 12,9, attached to Mac but also in Release as custom app with App Store)
  • Android: (not in active development)
  • UWP: -