UIKIT_EXTERN_CLASS 和 UIKIT_EXTERN，这两个常量是什么? [英] UIKIT_EXTERN_CLASS and UIKIT_EXTERN, for what these 2 constants are?

问题描述

当我在文档中定义类时，我总是在@interface 之前看到这两个东西(UIKIT_EXTERN_CLASS 和 UIKIT_EXTERN)，这些常量代表什么以及为什么 Apple 把它放在它们的类之前?

When i go to definition of classes in documentation, i always see these 2 things (UIKIT_EXTERN_CLASS and UIKIT_EXTERN) before the @interface, what these constants stand for and why Apple put it before their classes?

还有一件事，有文件 UIKitDefines.h，它包含所有这些定义/常量.

And one more thing, there is file UIKitDefines.h and it has all these definitions/constants.

#ifdef __cplusplus
#define UIKIT_EXTERN        extern "C" __attribute__((visibility ("default")))
#else
#define UIKIT_EXTERN            extern __attribute__((visibility ("default")))
#endif

#define UIKIT_STATIC_INLINE static inline
#define UIKIT_EXTERN_CLASS  __attribute__((visibility("default")))

推荐答案

看一看 此页面 来自 Apple 的开发人员文档.本质上，这些宏似乎允许您控制某些符号对应用程序其余部分的可见性.

Take a look at this page from Apple's developer documentation. In essence, it appears those macros allow you to control the visibility of certain symbols to the rest of your application.

这篇关于UIKIT_EXTERN_CLASS 和 UIKIT_EXTERN，这两个常量是什么?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！