main.dart

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

class AppModel extends Model {
  int _count = 0;

  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }

  void decrement() {
    _count--;
    notifyListeners();
  }
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Counter Example',
      theme: ThemeData.dark(),
      home: new ScopedModel<AppModel>(
        model: new AppModel(),
        child: new FirstScreen(),
      ),
    );
  }
}

class FirstScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('First Screen'),
      ),
      body: new Center(
        child: new RaisedButton(
            child: new Text('Launch new screen'),
            onPressed: () {
              Navigator.push(
                context,
                new MaterialPageRoute(builder: (context) => new Home()),
              );
            }),
      ),
    );
  }
}

class Home extends StatelessWidget {
  final AppModel appModelOne = new AppModel();
  final AppModel appModelTwo = new AppModel();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: new AppBar(
          title: new Text('Basic Counter'),
        ),
        body: Center(
          child: Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: <Widget>[
              ScopedModel<AppModel>(
                model: appModelOne,
                child: new Counter(
                  counterName: 'App Model One',
                ),
              ),
              ScopedModel<AppModel>(
                model: appModelTwo,
                child: Counter(
                  counterName: 'App Model Two',
                ),
              ),
            ],
          ),
        ));
  }
}

class Counter extends StatelessWidget {
  final String counterName;

  Counter({Key key, this.counterName});

  @override
  Widget build(BuildContext context) {
    return ScopedModelDescendant<AppModel>(
      builder: (context, child, model) => Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              new Text("$counterName:"),
              new Text(
                model.count.toString(),
                style: Theme.of(context).textTheme.display1,
              ),
              new ButtonBar(
                children: <Widget>[
                  new IconButton(
                    icon: new Icon(Icons.add),
                    onPressed: model.increment,
                  ),
                  new IconButton(
                    icon: new Icon(Icons.minimize),
                    onPressed: model.decrement,
                  )
                ],
              )
            ],
          ),
    );
  }
}