问题：
It is to my understanding that one should use a forward-class declaration in the event ClassA needs to include a ClassB header, and ClassB needs to include a ClassA header to avoid any circular inclusions. 据我了解，若是ClassA须要包括ClassB标头，而ClassB须要包括ClassA标头，以免任何循环包含，则应使用前向类声明。 I also understand that an #import is a simple ifndef so that an include only happens once. 我也理解#import是一个简单的ifndef所以一个include仅发生一次。 app
My inquiry is this: When does one use #import and when does one use @class ? 个人查询是：何时使用#import和什么时候使用@class ？ Sometimes if I use a @class declaration, I see a common compiler warning such as the following: 有时，若是我使用@class声明， @class看到常见的编译器警告，例如： ui
warning: receiver 'FooController' is a forward class and corresponding @interface may not exist.this
Would really love to understand this, versus just removing the @class forward-declaration and throwing an #import in to silence the warnings the compiler is giving me. 真的很想了解这一点，而不是仅仅删除@class前向声明，而后抛出#import来使编译器向我发出的警告静音。 url
解决方案：
参考一： https://stackoom.com/question/1LvB/class与-import参考二： https://oldbug.net/q/1LvB/class-vs-import