//'this is a placeholderwidget.dart'

class PlaceholderWidget extends StatelessWidget {
  final Color color;

  PlaceholderWidget(this.color);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: color,
    );
  }
}


//'this is home.dart'

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

class Home extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _HomeState();
  }
}

class _HomeState extends State<Home> {
  int _currentIndex = 0;
  final List<Widget> _children = [
    PlaceholderWidget(Colors.white),
    PlaceholderWidget(Colors.deepOrange),
    PlaceholderWidget(Colors.green),
    PlaceholderWidget(Colors.blueAccent)
  ];
  void onTabTapped(int index) {
    setState(() {
      _currentIndex = index;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: _children[_currentIndex],
      bottomNavigationBar: BottomNavigationBar(
          onTap: onTabTapped,
          currentIndex: _currentIndex,
          type: BottomNavigationBarType.fixed,
          selectedItemColor: Colors.black,
          unselectedItemColor: Colors.blue,
          items: [
            BottomNavigationBarItem(
              icon: new Icon(Icons.home),
              title: new Text('Home'),
            ),
            BottomNavigationBarItem(
              icon: new Icon(Icons.map),
              title: new Text('Map',
                ),
            ),
            BottomNavigationBarItem(
              icon: new Icon(Icons.language),
              title: new Text('Useful Links'),
            ),
            BottomNavigationBarItem(
              icon: new Icon(Icons.calendar_today),
              title: new Text('Calendar'),
            ),
          ]
      ),
    );
  }
}