@class和#import有什么区别 [英] What is the difference between @class and #import
问题描述
当我使用以下代码进行编译时，没有错误:
When I compile with the following code there are no errors:
@class RootViewController;
//#import "RootViewController.h"
使用以下代码进行编译时，出现错误:
When I compile with the following code I get an error:
//@class RootViewController;
#import "RootViewController.h"
错误:'RootViewController'之前的预期说明符-限定符列表"
"error: expected specifier-qualifier-list before 'RootViewController'"
我不明白两者之间的区别，因为我在类似的类中使用了#import，并且编译时没有错误！
I don't understand what the difference is between the two because I used #import in a similar class and it compiled without errors!
推荐答案
由于我仍然感到困惑，我决定参考该文档:
I decided to refer to the documentation because I was still confused:
#import
此伪指令与#include相同，不同之处在于它确保不会重复包含同一文件.因此，它是首选，并且在整个基于Objective-C的文档中的代码示例中代替#include来使用.
This directive is identical to #include, except that it makes sure that the same file is never included more than once. It’s therefore preferred and is used in place of #include in code examples throughout Objective-C–based documentation.
此约定意味着每个接口文件都间接包括所有继承类的接口文件.当源模块导入类接口时，它会获取该类所基于的整个继承层次结构的接口.
This convention means that every interface file includes, indirectly, the interface files for all inherited classes. When a source module imports a class interface, it gets interfaces for the entire inheritance hierarchy that the class is built upon.
@class
这样的声明只是使用类名作为类型，而不依赖于类接口的任何细节(其方法和实例变量)，@ class指令为编译器充分警告了所期望的内容.但是，在实际使用类接口的地方(创建实例，发送消息)，必须导入类接口.
Declarations like this simply use the class name as a type and don’t depend on any details of the class interface (its methods and instance variables), the @class directive gives the compiler sufficient forewarning of what to expect. However, where the interface to a class is actually used (instances created, messages sent), the class interface must be imported.
这篇关于@class和#import有什么区别的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
