main.dart

import 'package:flutter/material.dart';
import 'package:my_app/BlocProvider.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'test',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  int _count = 0;

  void _onButtonTapped() {
    setState(() {
      _count++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("test"),
      ),
      body: BlocProvider<MyBloc>(
        createBloc: () => MyBloc(_count),
        child: Center(
          child: Column(
            children: <Widget>[
              RaisedButton(
                onPressed: _onButtonTapped,
                child: Text("button"),
              ),
              MyBlocText()
            ],
          )
        ),
      ),
    );
  }
}

class MyBloc implements Bloc {
  final int num;

  MyBloc(this.num);

  dispose() {}
}

class MyBlocText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    MyBloc bloc = BlocProvider.of(context);
    return Text("${bloc.num}");
  }
}