bloc_example.dart

import 'dart:async';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final CounterBloc _counterBloc = CounterBloc();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("BLoC"),
      ),
      body: Center(
        child: StreamBuilder<int>(
          initialData: 0,
          stream: _counterBloc.outCounter,
          builder: (context, snapshot) {
            return Text(snapshot.data.toString(),
                style: Theme.of(context).textTheme.display1);
          },
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _counterBloc.incrementCount();
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

class CounterBloc {
  int _counter = 0;

  StreamController<int> _counterController = StreamController<int>();

  Stream<int> get outCounter => _counterController.stream;

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

  void incrementCount() {
    _counter++;
    _counterController.sink.add(_counter);
  }
}