How to show control's visibility with binding fast

Question

This is my ViewModel with bool and string property:

ViewModel : ValidatableBindableBase {
    private bool _isBusy;
    public bool IsBusy {
        get { return _isBusy; }
        set { SetProperty(ref _isBusy, value); }
    }

    private string _busyMessage;
    public string BusyMessage {
        get { return _busyMessage; }
        set { SetProperty(ref _busyMessage, value); }
    }

//Triggered when the button is clicked.
private async void Login() {
        ShowBusyOverlay("Signing in");
        // it will show if task.delay is added
        //await Task.Delay(5000);
        await loginService.SignIn();         
}

private async  void ShowBusyOverlay(string message) {
            IsBusy = true;
            BusyMessage = message;
    }
}

XAML: NOTE: on Windows 10 15063 Visibility can bind bool property without converter

<Grid Grid.RowSpan="3" Grid.ColumnSpan="3" Visibility="{Binding Path=IsBusy, UpdateSourceTrigger=PropertyChanged}">
        <Rectangle Fill="Black" Opacity="0.4" />
        <StackPanel VerticalAlignment="Center" HorizontalAlignment="Center">
            <ProgressRing IsActive="True" Width="40" Height="40"/>
            <TextBlock Text="{Binding BusyMessage}" FontSize="20" FontWeight="Thin"/>
        </StackPanel>
    </Grid>

Target:

It doesn't show the Grid fast enough , so It will navigate to other page without showing it , how can I show that loading/grid as soon as the it goes to my ShowBusyOverlay? and is it advisable?

why is `ShowBusyOverlay` async void? why use the dispatcher at all? — Haukinger, Oct 17 '19 at 06:06
setting properties on the view model does not require using the dispatcher — Haukinger, Oct 17 '19 at 06:57
there is but not called yet, cause I am testing the behavior. — Reaper, Oct 17 '19 at 07:16
where/how do you set the `DataContext`? do you see any binding errors? — Haukinger, Oct 17 '19 at 07:20
Im sorry ,I added a task.delay, and it is actually showing, BUT it is not showing fast , is there a way or it is advisable to show it fast? if yes, I will edit the question — Reaper, Oct 17 '19 at 08:10

score 1 · Answer 1 · answered Oct 18 '19 at 10:09

how can I show that loading/grid as soon as the it goes to my ShowBusyOverlay?

By activating it synchronously and then giving the UI thread time to update the screen.

Example:

private async void Login() 
{
    BusyMessage = message;
    IsBusy = true;
    await Task.Delay( TimeSpan.FromSeconds( 10 ) );
    IsBusy = false;
}

If, however, whatever task you're doing asynchronously is over rather quickly (or executing synchronously), the busy overlay will just flash or not appear at all. I'd make it fade in and out instead of immediately appearing/disappearing to reduce the visibility/annoyingness of the flashing.

How to show control's visibility with binding fast

1 Answers1