UWP Change loading state using binding and async functions

Question

I am coming from an Angular 2 and a C# back end background, so for the Angular side of things I am used to working with async functions and code, as well the C# background I understand the base libraries.

I am trying to create a simple page that has a a button, and a loading gif. You click the button the loading gif appears, 10 seconds later it disappears.

I can make the loading start no problem, but the nature of the async code jumps the execution and instantly makes the gif disappear.

How do I go about starting the spinner / making a gif visible, waiting 10 seconds in a non ui-blocking manner, and then finish with a thread-safe way of ending the animation / gif visibility?

View-Model code:

public class LoadingViewModel: INotifyPropertyChanged
    {
        private Visibility _loadingState;

        public event PropertyChangedEventHandler PropertyChanged = delegate { };

        public LoadingViewModel()
        {
            this._loadingState = Visibility.Collapsed;
        }

        public Visibility LoadingState
        {
            get {
                return this._loadingState;
            }
            set {
                this._loadingState = value;
                this.OnPropertyChanged();
            }
        }

        public void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            // Raise the PropertyChanged event, passing the name of the property whose value has changed.
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

MainView.xaml.cs:

public LoadingViewModel LoadingViewModel { get; set; }

        public MainPage()
        {
            this.InitializeComponent();
            this.LoadingViewModel = new LoadingViewModel();
        }


        private async Task BeginLoading()
        {
            LoadingViewModel.LoadingState = Visibility.Visible;
            await Task.Factory.StartNew(() =>
            {
                Task.Delay(TimeSpan.FromSeconds(10));

            }).ContinueWith(EndLoadingState);


        }

        //Updated and works but is there a better way?
        private async Task BeginLoading()
        {
            LoadingViewModel.LoadingState = Visibility.Visible;
            await Task.Factory.StartNew(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(10));
                await EndLoadingState(); //<-- New EndLoadingState doesn't accept parms
            });


        }

        private async void EndLoadingState(object state)
        {
            await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => {
                LoadingViewModel.LoadingState = Visibility.Collapsed;
            });
        }

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            await BeginLoading();
        }

And lastly a basic stack panel with my button and image:

<StackPanel Margin="10,144,0,144">
            <Button Content="Begin Loading for 10 seconds" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="0" Height="157" Width="366" FontSize="22" Background="{x:Null}" BorderThickness="5" BorderBrush="#FF58FF00" Click="Button_Click"/>
            <Image HorizontalAlignment="Center" Height="250" VerticalAlignment="Center" Width="250" Margin="0,25,0,0" Stretch="UniformToFill" Source="Assets/LoadingBubbles.gif" Visibility="{x:Bind Path=LoadingViewModel.LoadingState, Mode=TwoWay}"/>
        </StackPanel>

Yes sorry I am reading right now I am at work and had to move on from this problem for a short time. — Bailey Miller
– Bailey Miller, Commented Aug 4, 2017 at 14:05

Justin XL · Accepted Answer · 2017-08-02 21:41:20Z

First, try using a bool property in your LoadingViewModel instead of Visibility as the latter is a UI attribute. You generally don't want that in your ViewModel. If your target version of Windows 10 is 14393 or higher, you can bind it directly without a BoolToVisibilityConverter. And the binding doesn't need to be TwoWay also.

 Visibility="{x:Bind Path=LoadingViewModel.IsLoading, Mode=OneWay}"

Second, XAML binding will actually take care of dispatching the updated value onto the UI thread. So you can also get rid of Dispatcher.RunAsync and have a normal void method

private void EndLoadingState(object state)
{
    LoadingViewModel.IsLoading = false;
}

Finally, your BeginLoading method(best to rename it to BeginLoadingAsync) can be simplified to

private async Task BeginLoadingAsync()
{
    LoadingViewModel.IsLoading = true;

    await Task.Delay(TimeSpan.FromSeconds(10));

    EndLoadingState();
}

Hope this helps!

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