class _BTMAppBarState extends State<BTMAppBar> {
  int navigationIndex = 0;
  GlobalKey globalKey = new GlobalKey(debugLabel: 'btm_app_bar');

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      bottomNavigationBar: new BottomNavigationBar(
        key: globalKey,
        items: [
          new BottomNavigationBarItem(
              title: new Text("Tap 1"), icon: new Icon(Icons.people)),
          new BottomNavigationBarItem(
              title: new Text("Tap 2"), icon: new Icon(Icons.build)),
          new BottomNavigationBarItem(
              title: new Text("Tap 3"), icon: new Icon(Icons.favorite)),
        ],
        onTap: (int index) {
          setState(() {
            navigationIndex = index;
            switch (navigationIndex) {
              case 0:
                print("navigate to screen 1");
                break;
              case 1:
                print("navigate to screen 2");
                break;
              case 2:
                print("navigate to screen 3");
                break;
            }
          });
        },
      ),
      body: new Center(
        child: new RaisedButton(onPressed: () {
          final BottomNavigationBar navigationBar = globalKey.currentWidget;
          navigationBar.onTap(2);
        }),
      ),
    );
  }
}