private void _getTeachersByTeacherName_DoWork(object sender, DoWorkEventArgs e) { AvaliableTeachersListView.Dispatcher.InvokeAsync(() => { try { AvaliableTeachersListView.ItemsSource = _server.GetTeachersByName(TeacherNameTextBox.Text); } catch (Exception ex) { ErrorOrSuccessTextBlock.Dispatcher.InvokeAsync(() => { ErrorOrSuccessTextBlock.Text += ex; }); } }); Thread.Sleep(20); _progressBarWorker.CancelAsync(); }