WPF绑定未更新

Question

On my View model, I have the following property:

public Visibility IsModelBusy { get; set; }

I have a long processing task that does:

private void DoSomething(object obj)
{
    IsModelBusy = Visibility.Visible;
    OnPropertyChanged("IsModelBusy"); 
    DoHeavyWork();
    IsModelBusy = Visibility.Collapsed;
    OnPropertyChanged("IsModelBusy");
}

I have a UI element that is bound to IsModelBusy :

<Border Visibility="{Binding IsModelBusy, UpdateSourceTrigger=PropertyChanged}">
...
</Border>

PROBLEM My Border never gets visible and the main window hangs while the heavy task is ongoing (I can't run this in a background thread) I tried wrapping the property changed call in an action passed to a Dispatcher with no luck, the problem still persists.

Now if I do this:

private void DoSomething(object obj)
{
    IsModelBusy = Visibility.Visible;
    OnPropertyChanged("IsModelBusy"); 
    MessageBox.Show("What the...");  <=========
    DoHeavyWork();
    IsModelBusy = Visibility.Collapsed;
    OnPropertyChanged("IsModelBusy");
}

With the introduction of the MessageBox , the UI seems to process the property changed events and update correctly.

QUESTION Without using background tasks, how can I force the UI to process the PropertyChanged events?

Answer 1

You're blocking the UI thread with your DoHeavyWork() .

The Dispatcher cannot process any other operations (such as refreshing the UI) because it's busy executing your code.

Put that in a background thread.

Answer 2

After playing around with this a lot, I finally found the answers to my questions:

With the introduction of the MessageBox, the UI seems to process the property changed events and update correctly.

The message box forces the application to process its message queue, hence processing the property changed events and updating the UI.

Without using background tasks, how can I force the UI to process the PropertyChanged events?

There is no way around this - I kept the message box solution to force the UI to process all events