private void cmbUniversity_SelectionChanged(object sender, SelectionChangedEventArgs e) { cmbDepartment.IsEnabled = false; ComboBoxLogic comboboxLogic = new ComboBoxLogic(); ComboBoxModel sel = (ComboBoxModel)cmbUniversity.SelectedItem; cmbFaculty.IsEnabled = true; if (sel != null) cmbFaculty.ItemsSource = comboboxLogic.Faculties(sel.id); cmbFaculty.DataContext = EditData; cmbDepartment.ItemsSource = null; cmbDepartment.IsEnabled = false; }