符合NSObject的类中-self方法的目的是什么? [英] What is the purpose of the -self method in NSObject-conformant classes?

问题描述

就是这样.为什么有人要(至少作为公共API)这样的方法?有实际用途吗?

That's it. Why would anyone want (at least as a public API) a method such as that? Is there any practical use for it?

推荐答案

self方法对于键值编码(KVC)很有用.

The self method is useful for Key-Value Coding (KVC).

使用KVC，您可以将对象视为字典.您可以使用包含属性名称的字符串访问对象的属性，如下所示:[view valueForKey:@"superview"].您可以使用包含关键路径的字符串沿属性链向下移动，如下所示:[view valueForKeyPath:@"superview.superview.center"].

With KVC, you can treat an object somewhat like a dictionary. You can access a property of the object using a string containing the name of the property, like this: [view valueForKey:@"superview"]. You walk down a chain of properties using a string containing a key path, like this: [view valueForKeyPath:@"superview.superview.center"].

由于NSObject具有self方法，因此可以将self用作键或键路径:[view valueForKey:@"self"].因此，如果您以编程方式构造密钥路径，或者从文件中读取密钥路径，则使用"self"作为密钥可以避免编写特殊情况.

Since NSObject has a self method, you can use self as the key or key path: [view valueForKey:@"self"]. So if you're constructing your key paths programmatically, or reading them from a file, using "self" as a key may allow you to avoid writing a special case.

您还可以在谓词中使用self，如下所示:

You can also use self in predicates, like this:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self beginswith \"foo\""];
NSArray *filteredArray = [arrayOfStrings filteredArrayWithPredicate:predicate];

在这种情况下，我不知道NSPredicate是否实际上使用了self方法(也许通过KVC).当然有可能.

I don't know whether NSPredicate actually uses the self method (perhaps via KVC) in this case. It's certainly possible.

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