问题描述
在查看文档时，我几乎看不到任何重大差异。 value和object都是id 类型，因此可以是任何对象。 Key一次是字符串，另一种情况是id。其中一个似乎保留了对象，而另一个则没有。还有什么？哪一个适用于哪种情况？
When looking at the documentation, I hardly see any big difference. Both "value" and "object" are of type id, so can be any object. Key is once a string, and in the other case an id. One of them seems to retain the object, and the other don't. What else? Which one is for what case?
推荐答案
setValue：forKey： is 协议的一部分，除此之外，还允许您从Interface Builder等访问对象属性。 setValue：forKey：在 NSDictionary 以外的类中实现。
setValue:forKey: is part of the NSKeyValueCoding protocol, which among other things, lets you access object properties from the likes of Interface Builder. setValue:forKey: is implemented in classes other than NSDictionary.
setObject：forKey：是 NSMutableDictionary的存在的原因。它的签名恰好与setValue：forKey：非常相似，但更通用（例如任何键类型）。签名非常相似，这有点巧合。
setObject:forKey: is NSMutableDictionary's reason to exist. Its signature happens to be quite similar to setValue:forKey:, but is more generic (e.g. any key type). It's somewhat of a coincidence that the signatures are so similar.
令人困惑的是，NSMutableDictionary的 setValue：forKey：相当于 setObject：forKey：。在其他类中， setValue：forKey：更改成员变量。在 NSMutableDictionary 中，它会更改字典条目，除非您在键前加上@字符 - 在这种情况下它会修改成员变量。
What adds to the confusion is that NSMutableDictionary's implementation of setValue:forKey: is equivalent to setObject:forKey: in most cases. In other classes, setValue:forKey: changes member variables. In NSMutableDictionary, it changes dictionary entries, unless you prefix the key with a '@' character -- in which case it modifies member variables.
因此，简而言之，当您需要使用字典键和值时，使用 setObject：forKey：，并且 setValue：forKey：在极少数情况下你需要解决。
So, in a nutshell, use setObject:forKey: when you need to work with dictionary keys and values, and setValue:forKey: in the rarer cases where you need to tackle KVP.
编辑：哦，看起来这个问题已被问及之前回答：
and oh, it looks like this has been asked and answered before: Difference between objectForKey and valueForKey?
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