import 'dart:async';

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    title: 'Navigation Basics',
    home: FirstScreen(),
  ));
}

class FirstScreen extends StatefulWidget {

  @override
  State createState() => _FirstScreenState();
}


class _FirstScreenState extends State<FirstScreen> {

  Timer timer;
  int timerVal = 0;

  getData() {
    print('getData: ' + DateTime.now().toString());
    this.setState(() {
      timerVal++;
    });
  }

  @override
  void initState() {
    print('initState FirstScreen');
    super.initState();
    this.getData();
    timer = Timer.periodic(Duration(seconds: 2), (Timer t) => this.getData());
  }

  @override
  void dispose() {
    print('dispose FirstScreen');
    timer?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            Text('$timerVal', style: TextStyle(fontSize: 40.0),),
            RaisedButton(
              child: Text('Go to Second screen'),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => SecondScreen()),
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}



class SecondScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: RaisedButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => FirstScreen()),
            );
          },
          child: Text('Go to First screen!'),
        ),
      ),
    );
  }
}