RAC的源码阅读（二）

上篇已经介绍了RACSignal 冷热信号转换的源码跟踪，本篇主要介绍RACSubject 信号订阅及信号发送的源码跟踪

先贴一段示例代码，待会就对这段代码进行源码跟踪

//1️⃣RACSubject 创建
RACSubject * subject = [RACSubject subject];

//3️⃣ 订阅信号
[subject subscribeNext:^(id x) {
    NSLog(@"收到到:%@",x);
}];

//7️⃣ 发送数据
[subject sendNext:@"123"];

贴上我自绘的流程图

这个就是源码的执行步骤，接下来跟着这些步骤，就能弄懂整个源码流程

进入[[RACSubject alloc] init]

- (instancetype)init {
    self = [super init];
    if (self == nil) return nil;
    
    _disposable = [RACCompoundDisposable compoundDisposable];
    //2️⃣ 初始化订阅者列表
    _subscribers = [[NSMutableArray alloc] initWithCapacity:1];
    
    return self;
}

进入[subject subscribeNext] -> [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL]

+ (instancetype)subscriberWithNext:(void (^)(id x))next error:(void (^)(NSError *error))error completed:(void (^)(void))completed {
    //4️⃣ 初始化订阅者
    RACSubscriber *subscriber = [[self alloc] init];
    //5️⃣保存next,error,completed(Block)
    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];
    
    NSMutableArray *subscribers = self.subscribers;
    @synchronized (subscribers) {
        //6️⃣ 将新的订阅者添加到订阅者列表里面
        [subscribers addObject:subscriber];
    }
    
    [disposable addDisposable:[RACDisposable disposableWithBlock:^{
        @synchronized (subscribers) {
            // Since newer subscribers are generally shorter-lived, search
            // starting from the end of the list.
            NSUInteger index = [subscribers indexOfObjectWithOptions:NSEnumerationReverse passingTest:^ BOOL (id<RACSubscriber> obj, NSUInteger index, BOOL *stop) {
                return obj == subscriber;
            }];
            
            if (index != NSNotFound) [subscribers removeObjectAtIndex:index];
        }
    }]];
    
    return disposable;
}

进入[subject sendNext]

- (void)sendNext:(id)value {
    //8️⃣ 获取所有的订阅者 -- 通过这个block传回所有的订阅者
    [self enumerateSubscribersUsingBlock:^(id<RACSubscriber> subscriber) {
        //9️⃣ 获取到每个订阅者后执行每个sendNext方法,-->b
        [subscriber sendNext:value];
    }];
}

- (void)enumerateSubscribersUsingBlock:(void (^)(id<RACSubscriber> subscriber))block {
    NSArray *subscribers;
    @synchronized (self.subscribers) {
        subscribers = [self.subscribers copy];
    }
    //遍历所有的订阅者，将订阅者返回
    for (id<RACSubscriber> subscriber in subscribers) {
        block(subscriber);
    }
}

进入 [subscriber sendNext:value]

- (void)sendNext:(id)value {
    @synchronized (self) {
        void (^nextBlock)(id) = [self.next copy];
        if (nextBlock == nil) return;
        //1️⃣0️⃣ 执行订阅者保存下来的nextblock
        nextBlock(value);
    }
}

ps:本篇subject sendNext举例，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。

RAC的源码阅读（二）

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