import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> with TickerProviderStateMixin {
  static int _noOfTabs = 0;
  static List<Widget> _tabList;
  static List<Widget> _tabViewList;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: DefaultTabController(
            length: _noOfTabs,
            child: Scaffold(
              appBar: new AppBar(
                title: Text('Default TabBar Preview'),
                bottom: (_noOfTabs > 0)
                    ? TabBar(isScrollable: true, tabs: _tabList)
                    : null,
              ),
              body: (_noOfTabs > 0)
                  ? TabBarView(children: _tabViewList)
                  : Center(
                      child: Text('No tabs'),
                    ),
              floatingActionButton: FloatingActionButton(
                  child: Icon(Icons.add), onPressed: buttonPressed),
            )));
  }

  void buttonPressed() {
    setState(() {
      _noOfTabs++;
    });

    _tabList = new List<Widget>();
    _tabViewList = new List<Widget>();

    for (var i = 0; i < _noOfTabs; i++) {
      _tabList.add(Tab(text: 'Tab ' + (i + 1).toString()));
      _tabViewList.add(Center(child: Text('Tab ' + (i + 1).toString())));
    }
  }
}