本篇文章主要介绍了"KVO Considered Harmful ---Soroush Khanlou"，主要涉及到corners,require,Dictionary方面的内容，对于移动开发感兴趣的同学可以参考一下：
KVO Considered HarmfulI would normally title this something more clever, but I w...
KVO is the implicit way of updating with state changes. Tiny changes in one corner of your app can have ripple effects into other unexpected corners. You have no way of really keeping track of what’s being observed and by whom, and you have no way of using Xcode’s tools, like Command-click, to follow the path of code changes. The only thing you can hope to do is keep all your observations in your head at all times, which falls apart hopelessly as soon your app gets to any meaningful size or you add even one more person to your team.
A reader commented on Twitter with a great phrase that describes the problem exactly: he called KVO “a non-local implicit control flow change”. You’re essentially injecting code into setters at runtime from another object entirely.
When compared with a delegate pattern, KVO shows how weak it is in this area. For example, in most cases, there is only one delegate at any given time, simplifying which objects you need to check when problems arise. Since you have to implement a method with a custom selector, it is very easy to track down which objects in your app can ever even be the delegate for a particular protocol. It also provides casting and type information to its delegates, which reduces your reliance on guessing the type or checking at runtime with isKindOfClass: the way you have to with KVO.
KVO can cause infinite loops
You also have to make sure that you’re not changing the property that you’re observing when you’re responding to it, because then you’ll get another notification, ad infinitum. You never know if you’re changing another property that will also trigger a separate KVO notification, making debugging all the more difficult.
Of course, if you’re taking a lock when using your setter, your observers will be fired with that lock still held. Every time we think we have a grasp on the nuances of KVO, it hits us with a new problem.
