BLOC

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

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

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

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return CounterProvider(
      bloc: CounterBloc(),
      child: Scaffold(
        body: CounterHome(),
        floatingActionButton: CounterActionButton(),
      ),
    );
  }
}

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

class CounterHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    CounterBloc _counterBloc = CounterProvider.of(context).bloc;
    return Center(
      child: StreamBuilder(
        initialData: 0,
        stream: _counterBloc.count,
        builder: (context,snapshot){
          return ActionChip(
              label:Text('${snapshot.data}'),
              onPressed: (){
                _counterBloc.log('I am ActionChip !');
                _counterBloc.counter.add(2);
              });
          },
      ),
    );
  }
}

class CounterActionButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    CounterBloc _counterBloc = CounterProvider.of(context).bloc;
    return FloatingActionButton(
      child: Icon(Icons.add),
      onPressed:(){
        _counterBloc.log('I love you !');
        _counterBloc.counter.add(1);
        } ,
    );
  }
}

//共享数据类：这个类里面都是共享数据和共享方法；
class CounterBloc{
  int _count = 0;
  final _counterActionController = StreamController<int>();
  final _counterController = StreamController<int>();
  StreamSink<int> get counter => _counterActionController.sink;//不理解这句话的get
  Stream<int> get count=>_counterController.stream;
  CounterBloc(){
    _counterActionController.stream.listen(onData);
  }
  onData(int data){
    print('$data');
    _count=data+_count;
    _counterController.add(_count);
  }
  void dispose(){
    _counterActionController.close();
    _counterController.close();
  }
  void log(data){print(data);}
}

class CounterProvider extends InheritedWidget {
  final Widget child;//要共享的组件；
  final CounterBloc bloc;//要共享的数据；

  CounterProvider({
    this.bloc,
    this.child,
  }) :super(child: child);

   //定义一个便捷方法，方便子树中的widget获取共享数据
  static CounterProvider of(BuildContext context) {
    return context.inheritFromWidgetOfExactType(CounterProvider);
  }

  //该回调决定当data发生变化时，是否通知子树中依赖data的Widget  
  @override
  bool updateShouldNotify(CounterProvider old) {
    //如果返回true，则子树中依赖(build函数中有调用)本widget
    //的子widget的`state.didChangeDependencies`会被调用
    return old.bloc != bloc;
  }
}