private void cboP_SelectionChanged(object sender, SelectionChangedEventArgs e) { if (cboP.SelectedValue != null) { var value = cboP.SelectedValue.ToString(); cboD.ItemsSource = null; try { if (Provinces.Equals("-1")) { cboC.ItemsSource = null; return; } } catch { cboC.ItemsSource = null; return; } LoadCities(value); } }