main.dart

import 'package:flutter/material.dart';
import 'bottom_navi_bar.dart';

void main() => runApp(const App());

class App extends StatelessWidget {
  const App({Key key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: const _HomePage(),
    );
  }
}

class _HomePage extends StatefulWidget {
  const _HomePage({Key key}) : super(key: key);
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<_HomePage> {
  var _currentIndex = 1;
  void callback(int index) {
    setState(() {
      this._currentIndex = index;
      debugPrint("this._currentIndex:" + this._currentIndex.toString());
    });
  }

  @override
  Widget build(BuildContext context) {
    BottomNavigationDemo b = new BottomNavigationDemo(callback: callback);
    return Scaffold(
      body: Center(
        child: Text(this._currentIndex.toString()),
      ),
      bottomNavigationBar: b,
    );
  }
}