-(void)_test8{

    /// RACSubject继承自RACSignal 但是RACSubject和RACSignal的区别？

    //1能接收1，2

    //但是2只能接收2

    RACSubject *subject = [RACSubject subject];

    [subject subscribeNext:^(id x) {

        NSLog(@"订阅者1%@", x);

    }];

    [subject sendNext:@"subject1"];

    [subject subscribeNext:^(id x) {

        NSLog(@"订阅者2%@", x);

    }];

    [subject sendNext:@"subject2"];

}