如何在appbar颤动下滑动页面

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Scrollable Appbar Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: ScrollableAppbarPage(),
    );
  }
}

class ScrollableAppbarPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          SliverAppBar(
            title: Text('Scrollable Appbar Demo'),
            floating: true,
            expandedHeight: 200,
            flexibleSpace: Placeholder(),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              (BuildContext context, int index) {
                return ListTile(
                  title: Text('Item $index'),
                );
              },
              childCount: 100,
            ),
          ),
        ],
      ),
    );
  }
}