问题
Possible Duplicate:
Difference between inheritance and Categories in Objective-c
When should I use subclassing and when should I use categories?
回答1:
Subclass when you want to extend the functionality utilized by the base.
@interface MyObject: NSObject<SomeProtocol>
Add a category when you want to add a convenience method to code you may not control.
@interface UIView (MyViewAdditions)
- (void)recursiveEnumerateSubviewsUsingBlock:(void (^)(UIView *view, BOOL *stop))block;
来源：https://stackoverflow.com/questions/13344075/whats-the-difference-and-use-of-categories-and-inheritance