ios中@class和 #import,两种方式的讨论


这是因为h文件在修改后,所有import该h文件的所有文件必须重 新build,因此,如果把#import写在h文件中,import该h文件的文件也就会产生不必要的编译,增加编译时间,特别是在项目文件多的情况 下。想象一下,如果只是修改一个h文件而导致上百个文件不必要的编译,那是一件多么让人纠结的事情。。。




Randy Marsh:

When I develop, I have only three things in mind that never cause me any problems.

  1. Import super classes
  2. Import parent classes (when you have children and parents)
  3. Import classes outside your project (like in frameworks and libraries)

For all other classes (subclasses and child classes in my project self), I declare them via forward-class.



Simple answer: You #import or #include when there is a physical dependency. Otherwise, you use forward declarations (@class MONClass ,struct MONStruct , @protocol MONProtocol ).

Here are some common examples of physical dependence:

  • Any C or C++ value (a pointer or reference is not a physical dependency). If you have aCGPoint as an ivar or property, the compiler will need to see the declaration ofCGPoint .
  • Your superclass.
  • A method you use.