private void btnBuscar_Click(object sender, RoutedEventArgs e) { string patente = txtPatente.Text; //Check whether a TextBox is empty or not //Trim(): remove blank spaces from left and right if (patente.Trim() == "") { MessageBox.Show("Se debe ingresar una patente"); return; } //if not empty then: Automovil auto = _coleccion.BuscarAutomovil(patente); //if car doesn't exist in the collection, then: if (auto == null) { MessageBox.Show("No se ha encontrado la patente"); return; } //if car exists in the collection, then we pass car's attributes //to the form fields (MainWindows) cboMarca.SelectedIndex = (int)auto.Marca; txtModelo.Text = auto.Modelo; txtAnio.Text = auto.Anio.ToString(); chkNuevo.IsChecked = auto.Nuevo; if (auto.Transmision == Transmisiones.Automatica) { rbtAutomatica.IsChecked = true; } else { rbtMecanica.IsChecked = true; } }