通过下面一张图理解RACSignal的调用过程：
创建signale
RACSignal通过子类[RACDynamicSignal createSignal:]方法获得Signal，并将disSubscribe这个block保存在Signal中。
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
return [RACDynamicSignal createSignal:didSubscribe];
}
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
RACDynamicSignal *signal = [[self alloc] init];
signal->_didSubscribe = [didSubscribe copy];
return [signal setNameWithFormat:@"+createSignal:"];
}
创建subscriber
signal通过调用subscribeNext方法生成subscriber，并将next、error、completed block保存在subscriber中
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
NSCParameterAssert(nextBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
return [self subscribe:o];
}
+ (instancetype)subscriberWithNext:(void (^)(id x))next error:(void (^)(NSError *error))error completed:(void (^)(void))completed {
RACSubscriber *subscriber = [[self alloc] init];
subscriber->_next = [next copy];
subscriber->_error = [error copy];
subscriber->_completed = [completed copy];
return subscriber;
}
进行subscribe
第二步创建subscriber之后调用signal的subscribe方法，并将创建的subscriber作为参数。
这一步会生成RACCompoundDisposable和RACPassthroughSubscriber对象。
- RACCompoundDisposable：RACDisposable的子类，可以加入多个RACDisposable对象。当RACCompoundDisposable对象被dispose的时候，会dispose容器内的所有RACDisposable对象。
- RACPassthroughSubscriber：分别保存对RACSignal，RACSubscriber，RACCompoundDisposable的引用。通过RACPassthroughSubscriber对象来转发给真正的Subscriber。
- (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;
}
执行disSubscribe block
RACSignal通过RACScheduler.subscriptionScheduler来执行闭包，disSubscribe真正被调用的的位置就是上一步的RACDisposable *innerDisposable = self.didSubscribe(subscriber);
- (RACDisposable *)schedule:(void (^)(void))block {
NSCParameterAssert(block != NULL);
if (RACScheduler.currentScheduler == nil) return [self.backgroundScheduler schedule:block];
block();
return nil;
}
调用sendNext sendError sendCompleted
进入didSubscribe闭包后，调用sendNext:、sendError:、sendCompleted。由于第三步中将subscriber替换为RACPassthroughSubscriber对象，真正的subscriber被存储在RACPassthroughSubscriber对象中，即innerSubscriber，所以这一步的各种send方法其实是一个转发过程。
- (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];
}
- (void)sendError:(NSError *)error {
if (self.disposable.disposed) return;
if (RACSIGNAL_ERROR_ENABLED()) {
RACSIGNAL_ERROR(cleanedSignalDescription(self.signal), cleanedDTraceString(self.innerSubscriber.description), cleanedDTraceString(error.description));
}
[self.innerSubscriber sendError:error];
}
- (void)sendCompleted {
if (self.disposable.disposed) return;
if (RACSIGNAL_COMPLETED_ENABLED()) {
RACSIGNAL_COMPLETED(cleanedSignalDescription(self.signal), cleanedDTraceString(self.innerSubscriber.description));
}
[self.innerSubscriber sendCompleted];
}
执行next error completed闭包
通过调用innerSubscriber的sendNext:、sendError、和sendCompleted方法执行真正的subscriber中的next error completed闭包
- (void)sendNext:(id)value {
@synchronized (self) {
void (^nextBlock)(id) = [self.next copy];
if (nextBlock == nil) return;
nextBlock(value);
}
}
- (void)sendError:(NSError *)e {
@synchronized (self) {
void (^errorBlock)(NSError *) = [self.error copy];
[self.disposable dispose];
if (errorBlock == nil) return;
errorBlock(e);
}
}
- (void)sendCompleted {
@synchronized (self) {
void (^completedBlock)(void) = [self.completed copy];
[self.disposable dispose];
if (completedBlock == nil) return;
completedBlock();
}
}
过程回顾
去掉中间的繁杂细节，大致过程如下：
1.通过createSignal生成信号
2.通过subscribeNext确定信号内容到来时的处理方式
3.didSubscribe block块中异步处理完毕之后，进行sendNext、sendError和sendCompleted自动处理