Categories in Objective-c

The primary role of a category is to extend functionality, which means adding new methods and not encapsulating attributes.

If you want to add an attribute, you can use the associated object helper to implement

#import "Test.h" @interface Test (Other) @property (Nonatomic,strong) nsstring *mystr; @end

#import "Test+other.h"#import<objc/runtime.h>@implementationTest (Other)Static Const Char*omystr ="Omystr";-(void) Setmystr: (NSString *) mystr{objc_setassociatedobject (self, omystr, mystr, objc_association_retain_nonatomic);}-(nsstring*) mystr{returnObjc_getassociatedobject (self, omystr);;}@end

It is important to note the memory management semantics in the Setup method:

Association type	The equivalent @property property
Objc_association_assign	Assign
Objc_association_retain_nonatomic	Nonatomic, retain
Objc_association_copy_nonatomic	nonatomic, copy
Objc_association_retain	Retain
Objc_association_copy	Copy

Categories in Objective-c