Update UI async?

Question

Consider this example:

Private Sub Button_Click(
    sender As Button, e As RoutedEventArgs) Handles btn.Click

  sender.IsEnabled = False

  Thread.Sleep(50         


        

Answer 1

The button click event is handled by the UI thread, hence when you invoke thread.sleep you make the UI thread sleep, and you see no changes until the method ends.

Therefore you need to run the process on a new thread, and when the process ends, make the UI changes using the dispatcher.

For example:

Private event TaskEnded()
Private Sub Button_Click(sender As Button, e As RoutedEventArgs) Handles btn.Click
  btn.IsEnabled = False
  dim l as new Thread(sub()
                       Thread.Sleep(5000)
                       RaiseEvent TaskEnded
                       End Sub)
  l.start()
End Sub

Private Sub bla() Handles Me.TaskEnded
  dispatcher.BeginInvoke(sub()
                           btn.IsEnabled = True
                         end sub)
End Sub

The MVVM way you'll bind your button IsEnabled property to a boolean property in your viewModel, and update the VM propety instead on the button directly.