ios NSMutableDictionary 中 setObject:forKey: 和 setValue:forKey: 的区别在哪里？
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Where's the difference between setObject:forKey: and setValue:forKey: in NSMutableDictionary?
提问by Oren Trutner
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?
查看文档时，我几乎看不出有什么大的不同。"value" 和 "object" 都是 id 类型，所以可以是任何对象。Key 曾经是一个字符串，在另一种情况下是一个 id。其中一个似乎保留了对象，而另一个则没有。还有什么？哪个是针对什么情况的？
回答by Oren Trutner
setValue:forKey:is part of the NSKeyValueCodingprotocol, which among other things, lets you access object properties from the likes of Interface Builder. setValue:forKey:is implemented in classes other than NSDictionary.
setValue:forKey:是NSKeyValueCoding协议的一部分，除其他外，它允许您从 Interface Builder 等访问对象属性。setValue:forKey:在NSDictionary.以外的类中实现。
setObject:forKey:is NSMutableDictionary'sreason 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.
setObject:forKey:是NSMutableDictionary's存在的理由。它的签名恰好与 setValue:forKey: 非常相似，但更通用（例如任何键类型）。签名如此相似有点巧合。
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.
更令人困惑的是，在大多数情况下，NSMutableDictionary 的实现setValue:forKey:等效setObject:forKey:于。在其他类中，setValue:forKey:更改成员变量。在 中NSMutableDictionary，它会更改字典条目，除非您在键前添加一个“@”字符——在这种情况下，它会修改成员变量。
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.
因此，简而言之，setObject:forKey:当您需要使用字典键和值时使用，以及setValue:forKey:在需要处理KVP的极少数情况下使用。
EDIT: and oh, it looks like this has been asked and answered before: Difference between objectForKey and valueForKey?
编辑：哦，看起来之前已经问过并回答过：objectForKey 和 valueForKey 之间的区别？
回答by user102008
Another difference is that if you give a nil value to setValue:forKey:, it removes the key from the dictionary if it exists, otherwise does nothing. But if you give a nil value to setObject:forKey:, it raises an exception.
另一个区别是，如果给 一个 nil 值setValue:forKey:，它会从字典中删除键（如果存在），否则什么都不做。但是如果你给 一个 nil 值setObject:forKey:，它会引发一个异常。
回答by Jakub Truhlá?
-setValue:forKey:just send -setObject:forKey:to the receiver, unless the value is nil, in which case send -removeObjectForKey.
-setValue:forKey:只发送-setObject:forKey:给接收者，除非值是nil，在这种情况下发送-removeObjectForKey。
Dead simple.
死的简单。
回答by breakfreehg
anObject— The value for key. The object receives a retain message before being added to the NSDictionary. This value must not be nil.
anObject— 键的值。对象在被添加到NSDictionary. 该值不能为零。
aKey— The key for value. The key is copied (using copyWithZone:; keys must conform to the NSCopyingprotocol). The key must not be nil.
aKey— 值的键。密钥被复制（使用copyWithZone:; 密钥必须符合NSCopying协议）。键不能为零。
value— The value for key.
value— 键的值。
key— The key for value. Note that when using key-value coding, the key must be a string (see “Key-Value Coding Fundamentals”).
key— 值的键。请注意，使用键值编码时，键必须是字符串（参见“键值编码基础”）。
