flutter bloc基于InheritedWidget应用

#flutter bloc使用的三种方法#

BLoC：

BLoC表示为业务逻辑组件 (Business Logic Component)，而原理就是对StreamController的封装和延申出PublishSubject（普通广播的streamcontroll,可监听多次（默认异步）），BehaviorSubject（缓存最新一次事件的广播流控制器），ReplaySubject（缓存多个数据的广播流控制器，可以设定上限），做一个笔记，方便日后查看！

我们举一个例子说一下用法：

context.ancestorInheritedElementForWidgetOfExactType(type)?.widget;在flutter新版上方法已经过期。

过期方法：

 static T of<T extends BlocBase>(BuildContext context){
    final type = _typeOf<_BlocProviderInherited<T>>();
    _BlocProviderInherited<T> provider =
        context.ancestorInheritedElementForWidgetOfExactType(type)?.widget;
    return provider?.bloc;
  }

新方法：

  static T of<T extends BlocBase>(BuildContext context){
    // final type = _typeOf<_BlocProviderInherited<T>>();
    _BlocProviderInherited<T> provider =
        context.getElementForInheritedWidgetOfExactType<_BlocProviderInherited<T>>()?.widget;
    return provider?.bloc;
  }

构造BlocProvider

import 'package:flutter/material.dart';
Type _typeOf<T>() => T;

abstract class BlocBase {
  void dispose();
}

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

  final Widget child;
  final T bloc;

  @override
  _BlocProviderState<T> createState() => _BlocProviderState<T>();

  static T of<T extends BlocBase>(BuildContext context){
    final type = _typeOf<_BlocProviderInherited<T>>();
    _BlocProviderInherited<T> provider =
        context.ancestorInheritedElementForWidgetOfExactType(type)?.widget;
    return provider?.bloc;
  }
}

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

  @override
  Widget build(BuildContext context){
    return new _BlocProviderInherited<T>(
      bloc: widget.bloc,
      child: widget.child,
    );
  }
}

class _BlocProviderInherited<T> extends InheritedWidget {
  _BlocProviderInherited({
    Key key,
    @required Widget child,
    @required this.bloc,
  }) : super(key: key, child: child);

  final T bloc;

  @override
  bool updateShouldNotify(_BlocProviderInherited oldWidget) => false;
}

BlocProvider和之前一样正常使用：

T t = BlocProvider.of<T>(context);
LoginBloc loginBloc = BlocProvider.of<LoginBloc>(context);