ReactiveCocoa之RACSignal核心类的使用(三)
RACSignal使用步骤: 1.创建信号 + (RACSignal *)createSignal:(RACDisposable * (^)(id subscriber))didSubscribe 2.订阅信号,才会激活信号. - (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock 3.发送信号 - (vo