RACSignal解读

Posted 2021-10-07 王飞飞不会飞

• 使用

    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        NSLog(@"this is create block");
        [subscriber sendNext:@"发送Next"];
        return nil;
    }];
    
    [signal subscribeNext:^(id x) {
        NSLog(@"this is subscribe block %@",x);
    }];

• 源码

• + (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
  	return [RACDynamicSignal createSignal:didSubscribe];
  }
  

  继续看RACDynamicSignal createSignal的源码

  + (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
  	RACDynamicSignal *signal = [[self alloc] init];
  	signal->_didSubscribe = [didSubscribe copy];
  	return [signal setNameWithFormat:@"+createSignal:"];
  }

  上面源码干了2件事，初始化了RACDynamicSignal类型的信号，把didSubscribe Block 赋值给该信号作为其成员变量。

• 再来看订阅消息的源码

• - (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
  	NSCParameterAssert(nextBlock != NULL);
  	
  	RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
  	return [self subscribe:o];
  }

  新建一个RACSubscriber对象，把nextBlock作为o的一个成员变量。并作为subscribe 方法的参数，继续看subscribe方法的源码。注意这里的RACSignal的类型是RACDynamicSignal。所以要看RACDynamicSignal 的subscribe方法。

• - (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:^{
  			RACDisposable *innerDisposable = self.didSubscribe(subscriber);
  			[disposable addDisposable:innerDisposable];
  		}];
  
  		[disposable addDisposable:schedulingDisposable];
  	}
  	
  	return disposable;
  }

  这里是比较关键的代码，主要是如果有self.didSubscribe 就去执行，并且执行的参数为subscriber

        再继续看看这里的subscriber的初始化方法。

- (instancetype)initWithSubscriber:(id<RACSubscriber>)subscriber signal:(RACSignal *)signal disposable:(RACCompoundDisposable *)disposable {
	NSCParameterAssert(subscriber != nil);

	self = [super init];
	if (self == nil) return nil;

	_innerSubscriber = subscriber;
	_signal = signal;
	_disposable = disposable;

	[self.innerSubscriber didSubscribeWithDisposable:self.disposable];
	return self;
}

最后再看看sendNext的源码，注意这里didSubscribe block里面的subscribe类型应该是RACPassthroughSubscriber。所以要看 RACPassthroughSubscriber 的sendNext方法。

- (void)sendNext:(id)value {
	if (self.disposable.disposed) return;

	if (RACSIGNAL_NEXT_ENABLED()) {
		RACSIGNAL_NEXT(cleanedSignalDescription(self.signal), cleanedDTraceString(self.innerSubscriber.description), cleanedDTraceString([value description]));
	}

	[self.innerSubscriber sendNext:value];
}

这里其实就是把subscribeNext中传入的block执行了。

• 图解