How to show a WinForms Modal Dialog from a WPF App Thread

I have a WPF application. The main window of this application has a button. I am opening a WinForms modal dialog in a separate thread when this button is clicked. The trouble I am having is that the dialog does not beha开发者_Python百科ve like a modal i.e it is still possible to switch focus to the main window, whereas, I require to allow focus on the newly opened dialog and it should not be possible to select the main window.

Note: I cannot move the modalDialog.ShowDialog(); outside of the delegate because the dialog form creates controls dynamically and this means that these controls must remain on the thread that it was created. To be more clear, if I move the modalDialog.ShowDialog(); outside I will get an exception like so:

Cross-thread operation not vaild: Control 'DynamicList' accessed from a thread other than the one it was created on.

Any ideas as to how I might make the form behave as a modal?

Here is the code:

private void button1_Click(object sender, RoutedEventArgs e)
{
   DoSomeAsyncWork();
}

private void DoSomeAsyncWork()
{ 
  var modalDialog = new TestForm();
  var backgroundThread = new Thread((
     delegate()
     {
          // Call intensive method that creates dynamic controls
          modalDialog.DoSomeLongWaitingCall();
          modalDialog.ShowDialog();
     }
   ));
  backgroundThread.Start();
}

You should always create controls on the UI thread. If you do that, calling ShowDialog() through Dispatcher should work.