ReactiveObjC (前身是 ReactiveCocoa 或者 RAC) 是一个 Objective-C 框架，实现了函数响应式编程模式。
最简单的例子：
// When self.username changes, logs the new name to the console.
//
// RACObserve(self, username) creates a new RACSignal that sends the current
// value of self.username, then the new value whenever it changes.
// -subscribeNext: will execute the block whenever the signal sends a value.
[RACObserve(self, username) subscribeNext:^(NSString *newName) {
NSLog(@"%@", newName);
}];
K/V 通知
// Only logs names that starts with "j".
//
// -filter returns a new RACSignal that only sends a new value when its block
// returns YES.
[[RACObserve(self, username)
filter:^(NSString *newName) {
return [newName hasPrefix:@"j"];
}]
subscribeNext:^(NSString *newName) {
NSLog(@"%@", newName);
}];
