如何在颤动中用全局键制作StatefulWidget？

import 'package:flutter/material.dart';

final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

@override
Widget build(BuildContext context) {
  return Scaffold(
    key: _scaffoldKey,
    appBar: AppBar(
      title: Text('Flutter App'),
    ),
    body: Center(
      child: RaisedButton(
        onPressed: () {
          // 按钮点击事件
        },
        child: Text('按钮'),
      ),
    ),
  );
}

void _buttonClick() {
  _scaffoldKey.currentState.showSnackBar(
    SnackBar(
      content: Text('按钮被点击了'),
    ),
  );
}