如何在Screen类中使用Widget类

import 'package:flutter/material.dart';

class MyScreen extends StatefulWidget {
  @override
  _MyScreenState createState() => _MyScreenState();
}

class _MyScreenState extends State<MyScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My Screen'),
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            Text('Hello, World!'),
            RaisedButton(
              child: Text('Click Me'),
              onPressed: () {
                // 处理按钮点击事件
              },
            ),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyScreen(),
    );
  }
}