如何在向下滚动时隐藏AppBar

import 'package:flutter/material.dart';

class ScrollHideAppBar extends StatefulWidget {
  @override
  _ScrollHideAppBarState createState() => _ScrollHideAppBarState();
}

class _ScrollHideAppBarState extends State<ScrollHideAppBar> {
  ScrollController _scrollController;
  bool _isVisible;

  @override
  void initState() {
    super.initState();
    _scrollController = ScrollController();
    _isVisible = true;

    _scrollController.addListener(() {
      setState(() {
        _isVisible = _scrollController.position.userScrollDirection == ScrollDirection.forward;
      });
    });
  }

  @override
  void dispose() {
    _scrollController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: PreferredSize(
        preferredSize: Size.fromHeight(kToolbarHeight),
        child: AnimatedContainer(
          duration: Duration(milliseconds: 200),
          height: _isVisible ? kToolbarHeight : 0,
          child: AppBar(
            title: Text('Scroll Hide AppBar'),
          ),
        ),
      ),
      body: ListView.builder(
        controller: _scrollController,
        itemCount: 100,
        itemBuilder: (context, index) {
          return ListTile(
            title: Text('Item $index'),
          );
        },
      ),
    );
  }
}