参数类型“Widget”不能分配给参数类型“PreferredSizeWidget？”

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My App'),
        ),
        body: Center(
          child: MyPreferredSizeWidget(), // 使用PreferredSizeWidget类型的参数
        ),
      ),
    );
  }
}

class MyPreferredSizeWidget extends StatelessWidget implements PreferredSizeWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: 200,
      height: 100,
      color: Colors.blue,
      child: Text('My PreferredSizeWidget'),
    );
  }

  @override
  Size get preferredSize => Size.fromHeight(100); // 设置固定的大小
}