What is the difference between object(forKey:) and value(forKey:) in UserDefaults?

问题

I've set some user defaults using let userDefaults = UserDefaults.standard, and when I'm retrieving them, I can use any of these:

jobTextField.text = userDefaults.object(forKey: "job") as? String

OR I can use

jobTextField.text = userDefaults.value(forKey: "job") as? String

in what case this will has a difference? It'd be great to know when I can NOT use one of them.

Thanks a lot :)

回答1:

value(forKey:) is from key-value coding, and not a direct method of UserDefaults.

Never use value(forKey:) on UserDefaults or Dictionary or any other class unless you have a clearly understood need to use key-value coding to get the desired result.

When you don't have such a need, use the standard access methods provided by the class in question (such as UserDefaults object(forKey:).

回答2:

1. value(forKey:)

The two are completely different. The value(forKey:) is not a UserDefaults-only method. It is enabled by the NSKeyValueCoding, which, According to Apple's Documentation:

NSKeyValueCoding is an informal protocol that objects adopt to provide indirect access to their properties. When an object is key-value coding compliant, its properties are addressable via string parameters through a concise, uniform messaging interface.

It happens that UserDefaults is NSKeyValueCoding compliant, so people have started (not necessarily in the correct way) using it for accessing UserDefaults.

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2. object(forKey:)

This is the correct way to access UserDefaults's properties. Unless you do not have a very good reason to use value(forKey:), always use object(forKey:), or the other valid methods of UserDefaults (i.e. string(forKey:)).

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Hope this clears things up!

来源：https://stackoverflow.com/questions/42472327/what-is-the-difference-between-objectforkey-and-valueforkey-in-userdefault