}];
MAP操作，就是对某信号原来的返回值，做一个函数处理，让该信号返回一个新值。
Map的意思就是映射.
RACSignal *valid = [RACSignal combineLatest:@[_textView.rac_textSignal]
reduce:^(NSString *feedBackString) {
return @(feedBackString.length > 0);
}];
RAC(_feedButton, enabled) = valid;
RAC(_feedButton, alpha) =[valid map:^(NSNumber *b) {
return b.boolValue ? @1: @0.4;
}];
filter操作就是过滤信号。
如果block返回yes，信号有效。否则无效。
self.time = [NSDate date];
//每隔1秒发一个信号
RACSignal *repeatSignal = [[RACSignal interval:1 onScheduler:[RACScheduler mainThreadScheduler]] repeat];
[repeatSignal subscribeNext:^(NSDate *time) {
self.time = time;
}];
RACSignal *timeSignal = [self rac_valuesForKeyPath:@"time" observer:self];
//为信号量添加过滤block
[[timeSignal filter:^BOOL(NSDate* time) {
NSDateComponents *com = [[NSCalendar currentCalendar] components:NSCalendarUnitSecond fromDate:time];
return com.second % 2 == 0;
}] subscribeNext:^(NSDate* time) {
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"HH:mm:ss"];
self.label.text = [formatter stringFromDate:time];
}];
