Changing tabs with a callback function

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyTabbedPage(),
    );
  }
}

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

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

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

  TabController _tabController;

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

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Tab demo"),
        bottom: TabBar(
          controller: _tabController,
          tabs: myTabs,
        ),
      ),
      body: TabBarView(
        controller: _tabController,
        children: List.generate(
          myTabs.length,
          (i) {
            return MyTabPage(
              onButtonTap: () =>
                  _tabController.animateTo(i + 1 >= myTabs.length ? 0 : i + 1),
              onButtonTapWithIndex: _tabController.animateTo,
            );
          },
        ),
      ),
    );
  }
}

class MyTabPage extends StatelessWidget {
  final Function() onButtonTap;
  final Function(int) onButtonTapWithIndex;

  const MyTabPage({
    Key key,
    @required this.onButtonTap,
    @required this.onButtonTapWithIndex,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        RaisedButton(
          child: Text("Go to next tab"),
          onPressed: onButtonTap,
        ),
        RaisedButton(
          child: Text("Go to tab at index 1"),
          onPressed: () => onButtonTapWithIndex(1),
        )
      ],
    );
  }
}