private void CbxDepartments_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e) { var selectedDepartmentId = DepartmentId; ObservableCollection <StudyProgram> SP = new ObservableCollection <StudyProgram>(ServiceDataProvider.GetAllSPForDepartmentId(selectedDepartmentId)); if (SP.Count == 0) { e.Handled = true; } view.cbxStudyPrograms.ItemsSource = SP; }