RACSubject 与 RACReplaySubject
RACReplaySubject *replaySubject = [RACReplaySubject subject];
[replaySubject sendNext:@"RACReplaySubject可以先发送消息再订阅"];
[replaySubject subscribeNext:^(id x) {
NSLog(@"%@", x);
}];
RACSubject *subject = [RACSubject subject];
[subject subscribeNext:^(id x) {
NSLog(@"%@", x);
}];
[subject sendNext:@"subject只能先订阅再发送消息"];
