Flutter: Changing the current tab in tab bar view using a button

I am super late, but hopefully someone benefits from this. just add this line to your onPressed of your button and make sure to change the index number to your preferred index:

DefaultTabController.of(context).animateTo(1);

You can use TabController:

TabController _controller = TabController(
  vsync: this,
  length: 3,
  initialIndex: 0,
);

_controller.animateTo(_currentTabIndex);

return Scaffold(
  appBar: AppBar(
    bottom: TabBar(
      controller: _controller,
      tabs: [
        ...
      ],
    ),
  ),
  body: TabBarView(
    controller: _controller,
    children: [
      ...
    ],
  ),
);

And than, setState to update screen:

int _currentTabIndex = 0;

setState(() {
  _currentTabIndex = 1;
});

You need to get the TabBar controller and call its animateTo() method from the button onPressed() handle.

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',
      home: new MyTabbedPage(),
    );
  }
}

class MyTabbedPage extends StatefulWidget {
  const MyTabbedPage({Key key}) : super(key: key);

  @override
  _MyTabbedPageState createState() => new _MyTabbedPageState();
}

class _MyTabbedPageState extends State<MyTabbedPage> with SingleTickerProviderStateMixin {
  final List<Tab> myTabs = <Tab>[
    new Tab(text: 'LEFT'),
    new Tab(text: 'RIGHT'),
  ];

  TabController _tabController;

  @override
  void initState() {
    super.initState();
    _tabController = new TabController(vsync: this, length: myTabs.length);
  }

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

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Tab demo"),
        bottom: new TabBar(
          controller: _tabController,
          tabs: myTabs,
        ),
      ),
      body: new TabBarView(
        controller: _tabController,
        children: myTabs.map((Tab tab) {
          return new Center(child: new Text(tab.text));
        }).toList(),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: () => _tabController.animateTo((_tabController.index + 1) % 2), // Switch tabs
        child: new Icon(Icons.swap_horiz),
      ),
    );
  }
}

If you use a GlobalKey for the MyTabbedPageState you can get the controller from any place, so you can call the animateTo() from any button.

class MyApp extends StatelessWidget {
  static final _myTabbedPageKey = new GlobalKey<_MyTabbedPageState>();

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      home: new MyTabbedPage(
        key: _myTabbedPageKey,
      ),
    );
  }
}

You could call it from anywhere doing:

MyApp._myTabbedPageKey.currentState._tabController.animateTo(...);