How to hide app bar while scrolling up but shows up when scrolling down?

Question

I'm trying to achieve the behavior as we see in android WhatsApp and advised tab behavior in material design, check suggestion here and the video here. When i scroll down, I want the tab bar to be visible but the app bar to hide, this behaviour can be seen on the medium android app as well.

I saw there was an earlier answer here, but it did not work for me.

I've tried several approaches but the nested scroll view doesn't work for me.

 return DefaultTabController(
  length: 2,
  child:Scaffold(
    body: NestedScrollView(
      headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
        return <Widget>[
         SliverAppBar(
            title: Text("Application"),
            floating: true,
            pinned: true,
            snap: true,
            bottom: TabBar(
              tabs: <Tab>[
               Tab(text: "T"),
               Tab(text: "B"),
              ], // <-- total of 2 tabs
            ),
          ),
        ];
      },
      body: TabBarView(
        children: <Widget>[
         RandomWords(),
         RandomWords(),
        ], 
      ),
    ),
  ),
);

and tried this as well,

Scaffold(
   body: NestedScrollView(
     controller: _scrollViewController,
     headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
       return <Widget>[
         SliverAppBar(
           title: Text("N"),
           pinned: true,
           floating: true,
           forceElevated: innerBoxIsScrolled,
           //snap: true,
           bottom: TabBar(
             tabs: <Tab>[
              Tab(text: "T"),
              Tab(text: "B"),
             ],
             controller: _tabController,
           ),
         )
       ];
     },
     body: TabBarView(
       children: <Widget>[
         RandomWords(),
         RandomWords(),
       ],
       controller: _tabController,
     ),
   ),
 ),
);

My code is available here.

Is there any reason the NestedScrollView might not work?

Answer 1

Try This

import 'package:flutter/material.dart';

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

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

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 2,
      child: new Scaffold(
        body: new NestedScrollView(
          headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
            return <Widget>[
              new SliverAppBar(
                title: Text("Application"),
                floating: true,
                pinned: true,
                snap: true,
                bottom: new TabBar(
                  tabs: <Tab>[
                    new Tab(text: "T"),
                    new Tab(text: "B"),
                  ], // <-- total of 2 tabs
                ),
              ),
            ];
          },
          body: new TabBarView(
            children: <Widget>[
              Center(
                  child: Text(
                'T Tab',
                style: TextStyle(fontSize: 30),
              )),
              Center(
                  child: Text(
                'B Tab',
                style: TextStyle(fontSize: 30),
              )),
            ],
          ),
        ),
      ),
    );
  }
}

Output:

Answer 2

You can use SliverList and SliverAppBar