import 'package:flutter/material.dart';

void main() {
  runApp(
    new MaterialApp(
      home: new TestPage2(),
    ),
  );
}

class TestPage2 extends StatefulWidget {
  @override
  _TestPageState2 createState() => new _TestPageState2();
}

class _TestPageState2 extends State<TestPage2> {
  Widget _buildItem(BuildContext context, int index) {
    return new ListTile(
      title: new Text('Title $index'),
      subtitle: new Text('Subtitle $index'),
    );
  }

  Widget _buildTab(int listSize) {
    return new Builder(
      builder: (BuildContext context) {
        return new CustomScrollView(
          slivers: <Widget>[
            new SliverOverlapInjector(
              handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
            ),
            new SliverPersistentHeader(
              pinned: true,
              delegate: new FixedHeader(
                height: 48.0,
                child: new Material(
                  elevation: 4.0,
                  color: Colors.white,
                  child: new Container(
                    child: new Center(
                      child: const Text('Here my fixed header 1'),
                    ),
                  ),
                ),
              ),
            ),
            new SliverList(
              delegate: new SliverChildBuilderDelegate(
                _buildItem,
                childCount: listSize,
              ),
            ),
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return new RefreshIndicator(
      onRefresh: () {},
      child: new DefaultTabController(
        length: 2,
        child: new Scaffold(
          body: new NestedScrollView(
            headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
              return <Widget>[
                new SliverOverlapAbsorber(
                  handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                  child: new SliverAppBar(
                    backgroundColor: Colors.black26,
                    title: new Text('Here title'),
                    pinned: true,
                    floating: true,
                    bottom: new TabBar(
                      tabs: [
                        new Tab(text: 'Tab1'),
                        new Tab(text: 'Tab2'),
                      ],
                    ),
                  ),
                ),
              ];
            },
            body: new TabBarView(
              children: [
                _buildTab(30),
                _buildTab(5),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

class FixedHeader extends SliverPersistentHeaderDelegate {
  const FixedHeader({ this.height, this.child });

  final double height;

  final Widget child;

  @override
  double get minExtent => height;

  @override
  double get maxExtent => height;

  @override
  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
    return child;
  }

  @override
  bool shouldRebuild(FixedHeader oldDelegate) {
    return height != oldDelegate.height
        || child != oldDelegate.child;
  }
}