drawer_dialog.dart

class _MyHomePageState extends State<MyHomePage> {
  AlertDialog _dialog(String title) {
    return AlertDialog(
      title: Text(title),
      actions: <Widget>[
        FlatButton(
          child: Text('back'),
          onPressed: () {
            Navigator.pop(context);
          },
        ),
      ],
    );
  }
// ...   
}