If you want complete demonstration about this code please go to slcoderlk.blogspot.com to get full understanding. This code example show you how to change the content of the page without going to a new page(new route) like fragment in android SDK. This snippet used a drawer to change context but you can also use anything rather than a drawer.

fragment_flutter.dart

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Demo',
      theme: new ThemeData(
        primarySwatch: Colors.green,
      ),
      home: new HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return new HomePageState();
  }
}
class HomePageState extends State<HomePage> {
  int _index = 0;

  List<Text> _texts = [
    new Text('card 1'),
    new Text('card 2')
  ];

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: _texts[_index],
      ),
      drawer: new Drawer(
        child: new SafeArea(
          child: Column(
            children: <Widget>[
              new Column(
                children: [
                  new ListTile(
                    title: _texts[0],
                    selected: _index == 0,
                    onTap: () {
                      setState(() => _index = 0);
                      Navigator.of(context).pop();
                    },
                  ),
                  new ListTile(
                    title: _texts[1],
                    selected: _index == 1,
                    onTap: () {
                      setState(() => _index = 1);
                      Navigator.of(context).pop();
                    },
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
      body: new Center(
        child: _texts[_index],
      ),
    );
  }
}