#import和@class之间有什么区别，我应该什么时候使用一个呢？ [英] What's the difference between #import and @class, and when should I use one over the other?

问题描述

在过去的一个月里我一直在教自我Objective-C（我是一个Java头），我现在已经把大脑包裹了。有一件事，我现在困惑我：通过@class导入类和做一个#import有什么区别？

I've been teaching myself Objective-C over the past month or so (I'm a Java head) and I've got my brain wrapped around most of it now. One thing that's confusing me at the moment: What's the difference between importing a class via @class vs doing a #import?

一个比另一个更好，还是在某些情况下我需要使用一个而不是另一个？我目前只使用#import。

Is one better than another one, or do I need to use one instead of the other in certain cases? I've been using just #import so far.

推荐答案

#import 将整个头文件放入当前文件;还包括任何文件THAT文件 #import 。 @class，另一方面（当在一行上用一些类名称来使用时），只是告诉编译器嘿，你会很快看到一个新的令牌;它是一个类，所以这样对待它）。

#import brings the entire header file in question into the current file; any files that THAT file #imports are also included. @class, on the other hand (when used on a line by itself with some class names), just tells the compiler "Hey, you're going to see a new token soon; it's a class, so treat it that way).

当你有循环包含的潜力时，这是非常有用的;即Object1.h引用Object2，Object2.h引用Object1 。如果你 #import 两个文件到另一个，编译器可能会感到困惑，因为它试图 #import Object1。 h，查看并查看Object2.h;它尝试 #import Object2.h，并查看Object1.h等。

This is very useful when you've got the potential for 'circular includes'; ie, Object1.h makes reference to Object2, and Object2.h makes reference to Object1. If you #importboth files into the other, the compiler can get confused as it tries to #import Object1.h, looks in it and sees Object2.h; it tries to #import Object2.h, and sees Object1.h, etc.

另一方面，如果每个文件都有 @class Object1; 或 @class Object2; ，那么没有循环引用，只要确保实现<。c> c> #import 所需的头文件到您的实现（.m）文件。

If, on the other hand, each of those files has @class Object1; or @class Object2;, then there's no circular reference. Just be sure to actually #import the required headers into your implementation (.m) files.

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