什么是@selector？ [英] What actually is a @selector?

问题描述

有一些函数作为参数@selector（methodName）。我使用NSLog找出@selector是什么，它返回一个整数。它看起来像一个PID，但是当我运行ps ax无法找到PID。这个整数代表什么，为什么我们必须一直使用@selector，而不是只传递方法名？

There are some functions which take as an argument @selector(methodName). I used NSLog to find out what @selector is, and it returns an integer. It looks like a PID, but when I ran ps ax that PID could not be found. What does that integer represent and why do we have to use @selector all the time instead of just passing the method name?

推荐答案

@selector（）是一个编译器指令，将圆括号内的任何内容转换为 SEL 。 A SEL 是表示方法名称的类型，但不是方法实现。 （为了你需要一个不同的类型，可能是一个 IMP 或方法 SEL 被实现为 char * ，但是依赖于这种行为不是一个好主意。如果你想检查你有没有 SEL ，最好的方法是把它变成一个 NSString * 像这样：

@selector() is a compiler directive to turn whatever's inside the parenthesis into a SEL. A SEL is a type to indicate a method name, but not the method implementation. (For that you'd need a different type, probably an IMP or a Method) Under-the-hood, a SEL is implemented as a char*, although relying on that behavior is not a good idea. If you want to inspect what SEL you have, the best way to do it is to turn it into an NSString* like this:

NSLog(@"the current method is: %@", NSStringFromSelector(_cmd));

（假设你知道 _cmd 的每个方法调用的隐藏参数，并且是对应于当前方法的 SEL

(Assuming you know that _cmd is one of the hidden parameters of every method call, and is the SEL that corresponds to the current method)

a href =http://developer.apple.com/library/mac/#documentation/General/Conceptual/DevPedia-CocoaCore/Selector.html =nofollow noreferrer> Objective-C语言指南有更多关于这个主题的信息。

The Objective-C Programming Language Guide has much more information on the subject.

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