import 'package:flutter/material.dart';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(id: 1),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.id}) : super(key: key);

  final int id;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    print('Page ${widget.id} built!');
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.id.toString()),
      ),
      body: new Center(
        child: new RaisedButton(
          child: new Text('Open next page'),
          onPressed: () {
            Navigator.of(context).push(
              new MaterialPageRoute(
                builder: (_) => new MyHomePage(id: widget.id + 1),
                maintainState: true
              )
            );
          }
        )
      ),
    );
  }
}