Update ViewModel property from task - wpf

Question

I am building an app with WPF and Caliburn.Micro. I want to update a ProgressBar from an Task/Thread and I am wondering what I need to correctly update the UI:
public class DemoViewModel : PropertyChangedBase
{
private int m_Progress;
public int Progress
{
get { return m_Progress; }
set
{
if (value == m_Progress) return;
m_Progress = value;
NotifyOfPropertyChange();
NotifyOfPropertyChange(nameof(CanStart));
}
}
public bool CanStart => Progress == 0 || Progress == 100;
public void Start()
{
Task.Factory.StartNew(example);
}
private void example()
{
for (int i = 0; i < 100; i++)
{
Progress = i + 1; // this triggers PropertChanged-Event and leads to the update of the UI
Thread.Sleep(20);
}
}
}
From other programming languages I know that I need to synchronize with the UI thread to update the UI but my code just works. Is there something I missed and which could cause sporadic errors or is there some magic behind the scenes which care of the synchronization?

Answer 1

It will depend on how you've implemented INotifyPropertyChanged. The implementation should delgate all UI updates to the appropriate dispatcher.
Sample Implementation:
public void RaisePropertyChanged([CallerMemberName]string name) {
Application.Current.Dispatcher.Invoke(() => {
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}, System.Windows.Threading.DispatcherPriority.Background);
}
Also to clean up the task start a bit:
Edit:
Removed unnecessary bool return value, and set ConfigureAwait to stay off UI thread when task completes.
public async void Start()
{
await Task.Run(() => example()).ConfigureAwait(false);
}
private async Task example()
{
for (int i = 0; i < 100; i++)
{
Progress = i + 1; // this triggers PropertChanged-Event and leads to the update of the UI
await Task.Delay(20);
}
}