import 'package:flutter/material.dart';

void main() {
  runApp(A());
}

class A extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _AState();
  }

}

class _AState extends State<A> {
  double size = 100.0;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: DefaultTabController(
        length: 3,
        child: Scaffold(
          floatingActionButton: FloatingActionButton(
            onPressed: () {
              setState(() {
                if (size == 100) {
                  size = 0;
                } else {
                  size = 100;
                }
              });
            },
          ),
          appBar: AppBar(
            bottom: TabBar(
              tabs: [
                Tab(icon: Icon(Icons.directions_car)),
                Tab(icon: Icon(Icons.directions_transit)),
                Tab(icon: Icon(Icons.directions_bike)),
              ],
            ),
            title: Text('Tabs Demo'),
          ),
          body: SizedBox(
            width: size,
            height: size,
            child: TabBarView(
              children: [
                Icon(Icons.directions_car),
                Icon(Icons.directions_transit),
                Icon(Icons.directions_bike),
              ],
            ),
          ),
        ),
      ),
    );
  }
}