如何在flutter中返回SliverAppBar和SliverList的组合

import 'package:flutter/material.dart';

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          SliverAppBar(
            title: Text('My App'),
            expandedHeight: 200,
            flexibleSpace: FlexibleSpaceBar(
              background: Image.asset(
                'assets/images/header_image.jpg',
                fit: BoxFit.cover,
              ),
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              (BuildContext context, int index) {
                return ListTile(
                  title: Text('Item $index'),
                );
              },
              childCount: 20,
            ),
          ),
        ],
      ),
    );
  }
}