如何使ListView小部件与AppBar的底部永久相邻？

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('ListView with AppBar'),
        ),
        body: CustomScrollView(
          slivers: <Widget>[
            SliverAppBar(
              floating: true,
              bottom: PreferredSize(
                preferredSize: Size.zero,
                child: Container(), // 可以添加一些自定义的底部内容
              ),
            ),
            SliverList(
              delegate: SliverChildBuilderDelegate(
                (BuildContext context, int index) {
                  return ListTile(
                    title: Text('Item $index'),
                  );
                },
                childCount: 20,
              ),
            ),
          ],
        ),
      ),
    );
  }
}