Flutter 实现自动隐藏AppBar

有时候，当我们滑动列表时，希望AppBar可以自动隐藏，这一效果可以由两种方式实现：

1. SliverAppBar

详细代码：

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: NestedScrollView(
          headerSliverBuilder: _sliverBuilder,
          body: Center(
            child: Text('hahaha'),
          )),
    );
  }
}

List _sliverBuilder(BuildContext context, bool innerBoxIsScrolled) {
  return [
    SliverAppBar(
      centerTitle: true, //标题居中
      expandedHeight: 200.0, //展开高度200
      backgroundColor: Colors.tealAccent,
      floating: false, //不随着滑动隐藏标题
      pinned: false, //不固定在顶部
      flexibleSpace: FlexibleSpaceBar(
        centerTitle: true,
        background: Image.asset(
          "assets/pic.jpg", 
          fit: BoxFit.cover,
        ),
      ),
    )
  ];
}

2.  CustomScrollView

代码：

  _buildBody() {
    return CustomScrollView(
      physics: BouncingScrollPhysics(),
      slivers: [
        SliverAppBar(
          actions: [
            IconButton(
              icon: Icon(Icons.search, color: Color(0xffffffff)),
              onPressed: () {},
            ),
            IconButton(
              icon: Icon(Icons.refresh, color: Colors.white),
              onPressed: () {
                _setPoetryList();
              },
            )
          ],
          leading: _buildAppBarLeading(),
          floating: true,
        ),
        new SliverPadding(
          padding: const EdgeInsets.fromLTRB(0.0, 0.0, 0.0, 10.0),
          sliver: new SliverList(
            delegate: new SliverChildListDelegate(_getMainBody()),
          ),
        ),
      ],
    );
  }