31 Flutter: BottomNavigationBar

main.dart

import 'package:flutter/material.dart';

void main(){
  runApp(new MaterialApp(
    home: new MyApp(),
  ));
}

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

//State is information of the application that can change over time or when some actions are taken.
class _State extends State<MyApp>{

  List<BottomNavigationBarItem> _items;
  String _value = '';
  int _index = 0;

  @override
  //initState() is the default state or something which runs before the actual state or before the setState
  void initState() {
    _items = new List();
    _items.add(new BottomNavigationBarItem(icon: new Icon(Icons.people), title: new Text('People')));
    _items.add(new BottomNavigationBarItem(icon: new Icon(Icons.weekend), title: new Text('Weekend')));
    _items.add(new BottomNavigationBarItem(icon: new Icon(Icons.message), title: new Text('Message')));
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Name here'),
        backgroundColor: Colors.red,
      ),
      //hit Ctrl+space in intellij to know what are the options you can use in flutter widgets
      body: new Container(
        padding: new EdgeInsets.all(32.0),
        child: new Center(
          child: new Column(
            children: <Widget>[
              new Text(_value)
            ],
          ),
        ),
      ),
      bottomNavigationBar: new BottomNavigationBar(
          items: _items,
          fixedColor: Colors.blue,
          currentIndex: _index,
          onTap: (int item){
            _index = item;
            _value = "Current value is: ${_index.toString()}";
          },
      ),
    );
  }
}