类别和类扩展之间的区别? [英] Difference between Category and Class Extension?
问题描述
类别和类扩展之间有什么区别.我相信两者都用于在现有类中添加自定义方法.有人可以对此进行解释吗?带有代码的示例将不胜感激.
What is the difference between a Category and a Class Extension. I believe both are used to add custom methods in existing classes. Can someone throw light on this? Examplification with code will be really appreciated.
推荐答案
类别是一种向现有类添加方法的方法.它们通常驻留在名为"Class + CategoryName.h"的文件中，例如"NSView + CustomAdditions.h"(当然还有.m).
A category is a way to add methods to existing classes. They usually reside in files called "Class+CategoryName.h", like "NSView+CustomAdditions.h" (and .m, of course).
一个类扩展是一个类别，除了两个主要区别之外:
A class extension is a category, except for 2 main differences:
-
类别没有名称.声明如下:
The category has no name. It is declared like this:
@interface SomeClass ()
- (void) anAdditionalMethod;
@end
扩展名的实现必须在文件的主@implementation块中.
The implementation of the extension must be in the main @implementation block of the file.
在.m文件的顶部看到一个类扩展声明该类上的更多方法是很常见的，然后在该类的主要@implementation部分中实现这些方法.这是一种声明"pseudo-private"方法的方法(pseudo-private方法不是真正的私有方法，只是不对外公开).
It's quite common to see a class extension at the top of a .m file declaring more methods on the class, that are then implemented below in the main @implementation section of the class. This is a way to declare "pseudo-private" methods (pseudo-private in that they're not really private, just not externally exposed).
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