Instance Variables for Objective C Categories

Question

I have a situation where it seems like I need to add instance variables to a category, but I know from Apple\'s docs that I can\'t do that. So I\'m wondering what the best a

Answer 1

This is best achieved using the built-in ObjC feature Associated Objects (aka Associated References), in the example below just change to your category and replace associatedObject with your variable name.

NSObject+AssociatedObject.h

@interface NSObject (AssociatedObject)
@property (nonatomic, strong) id associatedObject;
@end

NSObject+AssociatedObject.m

#import 

@implementation NSObject (AssociatedObject)
@dynamic associatedObject;

- (void)setAssociatedObject:(id)object {
     objc_setAssociatedObject(self, @selector(associatedObject), object, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (id)associatedObject {
    return objc_getAssociatedObject(self, @selector(associatedObject));
}

See here for the full tutorial:

http://nshipster.com/associated-objects/