RAC的源码阅读（一）

简单介绍

    一个很出名的函数响应编程开源框架,可以帮助我们更简单快捷的处理事件

RAC中最常见的类

• RACSignal 信号类
  
• RACDisposable 它可以帮助我们取消订阅
  
• RACSubscriber 订阅者
  
• RACSubject 信号提供者

RAC 信号订阅发送的两种方式

• RACSignal  冷信号到热信号的转换
  
• RACSubject  能充当信号，又能发送信号

RACSignal 冷热信号转换的源码跟踪

先贴一段示例代码:

//1️⃣ RACSignal的创建
RACSignal *singal = [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber>  _Nonnull subscriber) {
    // 7️⃣
    [subscriber sendNext:@"123"];
    [subscriber sendNext:@"245"];
    return [RACDisposable disposableWithBlock:^{
        //信号取消订阅就会来这里,如有必要需要情况资源
    }];
}];

//3️⃣ RACSignal的订阅
RACDisposable *disponsable = [singal subscribeNext:^(id  _Nullable x) {
    NSLog(@"收到:%@",x);
}];

接下来根据我画的示例流程图来跟下源码

    先进入[RACSignal createSignal] --> [RACDynamicSignal createSignal]

+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
    //创建一个RACDynamicSignal对象
    RACDynamicSignal *signal = [[self alloc] init];
    //2️⃣ 把我们传入的block赋值给_didSubscribe变量
    signal->_didSubscribe = [didSubscribe copy];
    //返回
    return [signal setNameWithFormat:@"+createSignal:"];
}

    进入[RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];

+ (instancetype)subscriberWithNext:(void (^)(id x))next error:(void (^)(NSError *error))error completed:(void (^)(void))completed {
    //4️⃣ 创建订阅者
    RACSubscriber *subscriber = [[self alloc] init];
    //5️⃣ 保存nextBlock
    subscriber->_next = [next copy];
    subscriber->_error = [error copy];
    subscriber->_completed = [completed copy];
    
    return subscriber;
}

    进入[self subscribe:o]

- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
    NSCParameterAssert(subscriber != nil);
    
    RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable];
    subscriber = [[RACPassthroughSubscriber alloc] initWithSubscriber:subscriber signal:self disposable:disposable];
    
    if (self.didSubscribe != NULL) {
        RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
            //6️⃣ 执行RACSingal一开始保存的_didSubscribe，这一刻里面的信号就变成热信号
            RACDisposable *innerDisposable = self.didSubscribe(subscriber);
            [disposable addDisposable:innerDisposable];
        }];
        
        [disposable addDisposable:schedulingDisposable];
    }
    
    return disposable;
}

    进入[subscriber sendNext:]

- (void)sendNext:(id)value {
    @synchronized (self) {
        void (^nextBlock)(id) = [self.next copy];
        if (nextBlock == nil) return;
        // 8️⃣
        nextBlock(value);
    }
}

ps:请跟着流程图对源码进行阅读，关键点本人已加上注释。本人能力有限，有什么错误或者表达不清的还望指正。