Property changed is not being triggered inside a Task

Question

I have a simple app where I show a progress ring when some task is running and hide the progress ring as soon as it completes. Problem with this code is the Progress bar never gets collapsed. I keep a break point in the value converter class and it never receives a value of false even after the value changes. As a result the ProgressRing never collapses. Please help.

This is my ViewModel

public class TestVM : INotifyPropertyChanged
    {
        private bool _isRingVisible;
        public bool IsRingVisible
        {
            get => _isRingVisible;
            set
            {
                _isRingVisible = value;
                OnPropertyChanged(nameof(IsRingVisible));
            }
        }
        public TestVM()
        {
            Task.Run(async () => await DoSomething());
        }

        private async Task DoSomething()
        {
            IsRingVisible = true;
            await Task.Delay(5000);
            IsRingVisible = false; //Value set to false but when I have a break point in the value converter class, it never receives this value.
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

In the xaml I have a simple UI as follows,

<Page.Resources>
        <converter:BoolToVisibilityConverter x:Key="boolToVisibility"/>
    </Page.Resources>
<Grid>
        <Border x:Name="BdrProgressRing" 
                    Grid.Row="0" 
                    Grid.RowSpan="2" 
                    Background="Red"
                    VerticalAlignment="Center"
                    Opacity="0.6" 
                    Visibility="{x:Bind vm.IsRingVisible,Mode=OneWay,Converter={StaticResource boolToVisibility}}">
        </Border>
        <ProgressRing x:Name="PgRing" 
                          Grid.Row="0" 
                          Grid.RowSpan="2"
                          Visibility="{Binding ElementName=BdrProgressRing, Path=Visibility}"
                          IsActive="True"  
                          VerticalAlignment="Center"
                          Width="90"
                          Height="90"/>
    </Grid>

Here is my xaml.cs

public sealed partial class MainPage : Page
    {
        public TestVM vm { get; set; }
        public MainPage()
        {
            this.InitializeComponent();
            vm = new TestVM();
            this.DataContext = this;
        }
    }

Answer 1

Change

Task.Run(async () => await DoSomething()) ;

To

_ = DoSomething();

Probably you allowed to change the property only from Main UI Thread, not from pooled Task. Learn more about Synchronization Context in WPF.

---

However, the above is bad practice. Any async method should be awaited. Simply assigning the Task returned from DoSomething() to a local variable is not sufficient.

Since you can't await in a constructor, the view model should have a public awaitable method that is actually awaited by the caller, e.g.

public TestVM()
{
}

public Task Initialize()
{
    return DoSomething();
}

Then call await vm.Initialize(); in an async Loaded event handler in the view:

public MainPage()
{
    InitializeComponent();
    vm = new TestVM();
    DataContext = this;

    Loaded += async (s, e) => await vm.Initialize();
}