方法一

import 'package:flutter/material.dart';

class MessageScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    //因为本路由没有使用Scaffold，为了让子级Widget(如Text)使用
    //Material Design 默认的样式风格,我们使用Material作为本路由的根。
    return Material(
      child: CustomScrollView(
        slivers: <Widget>[
          //AppBar，包含一个导航栏
          SliverAppBar(
            pinned: true,
            expandedHeight: 250.0,
            flexibleSpace: FlexibleSpaceBar(
              titlePadding: EdgeInsets.fromLTRB(20, 40, 110, 10),
              centerTitle: false,
              title: const Text('Demo'),
              background: Image.asset(
                "./images/sliverAppBar_bg.png", fit: BoxFit.cover,),
            ),
          ),

          SliverPadding(
            padding: const EdgeInsets.all(8.0),
            sliver: new SliverGrid( //Grid
              gridDelegate: new SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: 2, //Grid按两列显示
                mainAxisSpacing: 10.0,
                crossAxisSpacing: 10.0,
                childAspectRatio: 4.0,
              ),
              delegate: new SliverChildBuilderDelegate(
                    (BuildContext context, int index) {
                  //创建子widget      
                  return new Container(
                    alignment: Alignment.center,
                    color: Colors.cyan[100 * (index % 9)],
                    child: new Text('grid item $index'),
                  );
                },
                childCount: 20,
              ),
            ),
          ),
          //List
          new SliverFixedExtentList(
            itemExtent: 50.0,
            delegate: new SliverChildBuilderDelegate(
                    (BuildContext context, int index) {
                  //创建列表项      
                  return new Container(
                    alignment: Alignment.center,
                    color: Colors.lightBlue[100 * (index % 9)],
                    child: new Text('list item $index'),
                  );
                },
                childCount: 50 //50个列表项
            ),
          ),
        ],
      ),
    );
  }
}

方法二

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

关于sliverAppBar中pinned、floating、snap三个属性搭配使用产生的效果，请移步到这里