`DialogHost.WaitFor*` methods not waiting for animation to finish

[corvinsz]

Bug explanation

related PR #4083

The DialogHost.WaitForClosed() and DialogHost.WaitForOpened() methods don't wait until the closing/opening animation is actually finished.

Here is an example where the background is set to red after closing the dialog and using the new WaitForClosed() method:

mdixWaitFor.mp4

Repro:

private async void Button_Click(object sender, RoutedEventArgs e)
{
    var dialogContent = new Button()
    {
        Content = "Close",
        Margin = new Thickness(400)            
    };
    dialogContent.Click += (_, _) => DialogHost.Close("RootDialog");

    await DialogHost.Show(dialogContent, "RootDialog");
    var sw = Stopwatch.StartNew();
    await DialogHost.WaitForClosed("RootDialog");
    sw.Stop();
    Debug.WriteLine($"WaitForClosed: {sw.ElapsedMilliseconds}ms");

    // Do some UI work
    if (App.Current.MainWindow.Background == System.Windows.Media.Brushes.Red)
    {
        App.Current.MainWindow.Background = System.Windows.Media.Brushes.Green;
    }
    else
    {
        App.Current.MainWindow.Background = System.Windows.Media.Brushes.Red;
    }
}

The output shows the call to await DialogHost.WaitForClosed("RootDialog"); is not waiting for anything:
WaitForClosed: 0ms

Version

latest main