stream_providers.dart

import 'dart:async';

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

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

class Counter {
  final int count;
  final String name;

  Counter(this.count, this.name);
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: CounterPage.init(context),
    );
  }
}

class CounterProvider {
  final _counterController = StreamController<Counter>();
  Stream<Counter> get streamCounter => _counterController.stream;

  final _sliderController = StreamController<int>();
  Stream<int> get streamSlider => _sliderController.stream;

  int _count = 0;

  void increment() {
    _count = _count + 1;
    _counterController.add(Counter(_count, 'diego'));
  }

  void decrement() {
    _count = _count - 1;
    _counterController.add(Counter(_count, 'diego'));
  }

  void onChange(double val) {
    _sliderController.add(val.toInt());
  }

  void dispose() {
    _sliderController.close();
    _counterController.close();
  }
}

class CounterPage extends StatefulWidget {
  CounterPage._();

  static Widget init(BuildContext context) {
    final provider = CounterProvider();
    return MultiProvider(
      providers: [
        Provider<CounterProvider>(
          create: (_) => provider,
        ),
        StreamProvider<Counter>(
          create: (_) => provider.streamCounter,
        ),
        StreamProvider<int>(
          create: (_) => provider.streamSlider,
        )
      ],
      child: CounterPage._(),
    );
  }

  @override
  _CounterPageState createState() => _CounterPageState();
}

class _CounterPageState extends State<CounterPage> {
  @override
  void dispose() {
    Provider.of<CounterProvider>(context, listen: false).dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final provider = Provider.of<CounterProvider>(context, listen: false);
    print('rebuild');
    return Scaffold(
      appBar: AppBar(
        title: Text('Counter App'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Consumer<Counter>(builder: (context, value, _) {
              final c = value?.count;
              return Text(
                '${c?.toString() ?? 0}',
                style: TextStyle(fontSize: 80.0),
              );
            }),
            SizedBox(
              height: 20.0,
            ),
            Consumer<int>(builder: (context, value, _) {
              return Slider(
                value: value?.toDouble() ?? 1,
                min: 1,
                max: 100,
                onChanged: provider.onChange,
              );
            }),
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                FloatingActionButton(
                  onPressed: provider.increment,
                  child: Icon(Icons.add),
                  tooltip: 'Increment',
                ),
                SizedBox(width: 20.0),
                FloatingActionButton(
                  onPressed: provider.decrement,
                  child: Icon(Icons.remove),
                  tooltip: 'Decrement',
                ),
              ],
            )
          ],
        ),
      ),
    );
  }
}