private void DeleteQuestion_Click(object sender, RoutedEventArgs e)
 {
     if (listBox.SelectedItem != null)
     {
         _contentManager.DeleteQuestion((listBox.SelectedItem as Question).ID, _selectedQuiz);
         questions.Remove(listBox.SelectedItem as Question);
         EditQuestion.IsEnabled   = false;
         DeleteQuestion.IsEnabled = false;
         _saved         = false;
         Save.IsEnabled = true;
     }
 }