flutter fix tabbar in top of screen when i scroll the view

like with Instagram in profile page of that, i want to fix Tabbar on top of screen when i scroll the view, for example:

i think i should implementing that with SliverAppBar, this is my code, but it doesn't work correctly and in that top of tab elements will be change height

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

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

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  TabController _tabController;
  ScrollController _scrollViewController;

  @override
  void initState() {
    super.initState();
    _tabController = TabController(vsync: this, length: 2);
    _scrollViewController = ScrollController(initialScrollOffset: 0.0);
  }

  @override
  void dispose() {
    _tabController.dispose();
    _scrollViewController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: NestedScrollView(
        controller: _scrollViewController,
        headerSliverBuilder: (BuildContext context, bool boxIsScrolled) {
          return <Widget>[
            SliverAppBar(
              title: Column(
                children: <Widget>[
                  Container(
                    height: 200.0,
                    color: Colors.green,
                  ),
                  Container(
                    height: 200.0,
                    color: Colors.yellow,
                  ),

                ],
              ),
              pinned: true,
              floating: true,
              forceElevated: boxIsScrolled,
              bottom: TabBar(
                tabs: <Widget>[
                  Tab(
                    text: "Home",
                    icon: Icon(Icons.home),
                  ),
                  Tab(
                    text: "Example page",
                    icon: Icon(Icons.help),
                  )
                ],
                controller: _tabController,
              ),
            )
          ];
        },
        body: TabBarView(
          children: <Widget>[
            PageOne(),
            PageTwo(),
          ],
          controller: _tabController,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.control_point),
        onPressed: () {
          _tabController.animateTo(1,
              curve: Curves.bounceInOut, duration: Duration(milliseconds: 10));

          // _scrollViewController.animateTo(
          //     _scrollViewController.position.minScrollExtent,
          //     duration: Duration(milliseconds: 1000),
          //     curve: Curves.decelerate);

          _scrollViewController
              .jumpTo(_scrollViewController.position.maxScrollExtent);
        },
      ),
    );
  }
}

class PageOne extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Image.asset(
            'assets/photos/wallpaper-1.jpg',
            width: 200.0,
          ),
          Image.asset(
            'assets/photos/wallpaper-2.jpg',
            width: 200.0,
          ),
          Image.asset(
            'assets/photos/wallpaper-3.jpg',
            width: 200.0,
          ),
        ],
      ),
    );
  }
}

class PageTwo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemExtent: 250.0,
      itemBuilder: (context, index) => Container(
        padding: EdgeInsets.all(10.0),
        child: Material(
          elevation: 4.0,
          borderRadius: BorderRadius.circular(5.0),
          color: index % 2 == 0 ? Colors.cyan : Colors.deepOrange,
          child: Center(
            child: Text(index.toString()),
          ),
        ),
      ),
    );
  }
}