BLoC 架构

[OPY-bbt]

Business Logic Component

事实上，BLoC模式最初被设想为允许独立于平台重用相同的代码 youtube

设计规范

• 输入，输出必须是Streams/Sinks
• 依赖必须是可注入的
• 平台无关性

UI 设计规范

• 每个复杂的组件都应该有对应的BLoC（具体还要自己判断）
• 组件应该原样发送输入（比如input change事件，组件内不应该处理value，而是发送给BLoC处理）
• 组件应该原样展示数据 （这和上面一点说的有点重复。。）
• BLoC应该有唯一的输出（而不是输出A，B,然后在组件里merge）

[OPY-bbt]

用流重写计数器的例子

import 'dart:async';

import 'package:flutter/material.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  StreamController _ctrl = StreamController<int>();

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    _ctrl.close();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<int>(
              stream: _ctrl.stream,
              initialData: _counter,
              builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                return Text(
                  '${snapshot.data}',
                  style: Theme.of(context).textTheme.display1,
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _ctrl.sink.add(++_counter);
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

[OPY-bbt]

用BLoC重写计数器的例子

import 'dart:async';

import 'package:flutter/material.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    final IncrementBloc bloc = IncrementBloc();
    // TODO: implement build
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<int>(
              stream: bloc.ctrl.stream,
              initialData: bloc.counter,
              builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                return Text(
                  '${snapshot.data}',
                  style: Theme.of(context).textTheme.display1,
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: bloc.add,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class IncrementBloc {
  int counter = 0;
  StreamController ctrl = StreamController<int>();

  @override
  void dispose() {
    ctrl.close();
  }

  add() {
    ctrl.sink.add(++counter);
  }
}

但是虽然组件都变成了statelessWidget。dispose应该放在哪里呢？所以还是需要一个statefulWidget组件来释放资源。

[OPY-bbt]

增加BlocProvider

import 'dart:async';

import 'package:flutter/material.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: BlocProvider(
        bloc: IncrementBloc(),
        child: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    final IncrementBloc bloc = BlocProvider.of<IncrementBloc>(context);
    // TODO: implement build
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<int>(
              stream: bloc.ctrl.stream,
              initialData: bloc.counter,
              builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                return Text(
                  '${snapshot.data}',
                  style: Theme.of(context).textTheme.display1,
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: bloc.add,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

//所有BLoC的通用接口
abstract class BlocBase {
  void dispose();
}

class IncrementBloc implements BlocBase {
  int counter = 0;
  StreamController ctrl = StreamController<int>();

  @override
  void dispose() {
    ctrl.close();
  }

  add() {
    ctrl.sink.add(++counter);
  }
}

//通用BLoC提供商
class BlocProvider<T extends BlocBase> extends StatefulWidget {
  BlocProvider({
    Key key,
    @required this.child,
    @required this.bloc,
  }) : super(key: key);

  final T bloc;
  final Widget child;

  static T of<T extends BlocBase>(BuildContext context) {
    var type = _typeOf<BlocProvider<T>>();
    BlocProvider<T> provider = context.ancestorWidgetOfExactType(type);
    return provider.bloc;
  }

  static Type _typeOf<T>() => T;

  @override
  _BlocProviderState createState() {
    // TODO: implement createState
    return _BlocProviderState();
  }
}

class _BlocProviderState<T> extends State<BlocProvider<BlocBase>> {
  @override
  void dispose() {
    // TODO: implement dispose
    widget.bloc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return widget.child;
  }
}

[OPY-bbt]

引入rxdart

import 'package:flutter/material.dart';
import 'package:rxdart/rxdart.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: BlocProvider(
        bloc: IncrementBloc(),
        child: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    final IncrementBloc bloc = BlocProvider.of<IncrementBloc>(context);
    // TODO: implement build
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<int>(
              stream: bloc.stream,
              initialData: bloc.counter,
              builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                return Text(
                  '${snapshot.data}',
                  style: Theme.of(context).textTheme.display1,
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: bloc.add,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

//所有BLoC的通用接口
abstract class BlocBase {
  void dispose();
}

class IncrementBloc implements BlocBase {
  int counter = 0;
  BehaviorSubject<int> _controller = BehaviorSubject<int>();

  Stream<int> get stream => _controller.stream;

  @override
  void dispose() {
    _controller.close();
  }

  add() {
    _controller.sink.add(++counter);
  }
}

//通用BLoC提供商
class BlocProvider<T extends BlocBase> extends StatefulWidget {
  BlocProvider({
    Key key,
    @required this.child,
    @required this.bloc,
  }) : super(key: key);

  final T bloc;
  final Widget child;

  static T of<T extends BlocBase>(BuildContext context) {
    var type = _typeOf<BlocProvider<T>>();
    BlocProvider<T> provider = context.ancestorWidgetOfExactType(type);
    return provider.bloc;
  }

  static Type _typeOf<T>() => T;

  @override
  _BlocProviderState createState() {
    // TODO: implement createState
    return _BlocProviderState();
  }
}

class _BlocProviderState<T> extends State<BlocProvider<BlocBase>> {
  @override
  void dispose() {
    // TODO: implement dispose
    widget.bloc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return widget.child;
  }
}

[OPY-bbt]

引入 flutter_bloc

import 'package:bloc/bloc.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: BlocProvider(
        create: (BuildContext context) => IncrementBloc(),
        child: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    final IncrementBloc bloc = BlocProvider.of<IncrementBloc>(context);

    // TODO: implement build
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            BlocBuilder<IncrementBloc, int>(
              builder: (BuildContext context, counter) {
                return Text(
                  '$counter',
                  style: Theme.of(context).textTheme.display1,
                );
              },
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          bloc.add(CounterEvent.add);
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

enum CounterEvent { add }

class IncrementBloc extends Bloc<CounterEvent, int> {
  @override
  int get initialState => 0;

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    switch (event) {
      case CounterEvent.add:
        yield state + 1;
        break;
    }
  }
}