ReactiveCocoa-响应式编程中的一个开源矿建，相当于KVO
in 知识 on Object-c
https://github.com/ReactiveCocoa/ReactiveObjC
IOS响应式编程框架ReactiveCocoa(RAC)使用示例
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in 知识 on Object-c
https://github.com/ReactiveCocoa/ReactiveObjC
IOS响应式编程框架ReactiveCocoa(RAC)使用示例