Objective-C: Property / instance variable in category

by

.h-file

@interface NSObject (LaserUnicorn)

@property (nonatomic, strong) LaserUnicorn *laserUnicorn;

@end

.m-file

#import <objc/runtime.h>

static void * LaserUnicornPropertyKey = &LaserUnicornPropertyKey;

@implementation NSObject (LaserUnicorn)

- (LaserUnicorn *)laserUnicorn {
    return objc_getAssociatedObject(self, LaserUnicornPropertyKey);
}

- (void)setLaserUnicorn:(LaserUnicorn *)unicorn {
    objc_setAssociatedObject(self, LaserUnicornPropertyKey, unicorn, OBJC_ASSOCIATION_RETAIN_NONATOMIC); 
}

@end

Just like a normal property – accessible with dot-notation

NSObject *myObject = [NSObject new];
myObject.laserUnicorn = [LaserUnicorn new];
NSLog(@"Laser unicorn: %@", myObject.laserUnicorn);

Easier syntax

Alternatively you could use @selector(nameOfGetter) instead of creating a static pointer key like so:

- (LaserUnicorn *)laserUnicorn {
    return objc_getAssociatedObject(self, @selector(laserUnicorn));
}

- (void)setLaserUnicorn:(LaserUnicorn *)unicorn {
    objc_setAssociatedObject(self, @selector(laserUnicorn), unicorn, OBJC_ASSOCIATION_RETAIN_NONATOMIC); 
}

For more details see https://stackoverflow.com/a/16020927/202451

More Related Contents:

  1. Overriding methods using categories in Objective-C
  2. How do I use objc_setAssociatedObject/objc_getAssociatedObject inside an object?
  3. What is the difference between inheritance and Categories in Objective-C
  4. Is calling super in a category the same as calling it in a subclass?
  5. What happens if two ObjC categories override the same method?
  6. Defining categories for protocols in Objective-C?
  7. Using Super in an Objective C Category?
  8. How do I call a -(void) method from a -(IBaction) method?
  9. Using NSDateFormatter in objective-C [duplicate]
  10. How do I declare class-level properties in Objective-C?
  11. What is the Swift equivalent of respondsToSelector?
  12. setValue:forUndefinedKey: this class is not key value coding-compliant for the key [duplicate]
  13. UIPopoverPresentationController on iOS 8 iPhone
  14. Rounding numbers in Objective-C
  15. Difference between @interface definition in .h and .m file
  16. Are ints always initialized to 0?
  17. Handling Pointer-to-Pointer Ownership Issues in ARC
  18. Core Data NSPredicate “deleted == NO” does not work as expected
  19. XCode 5 unit testing: starts my app
  20. Tagged pointers in Objective-C
  21. Animated gif not working in MKMapView overlay using MKOverlayRenderer
  22. Replace all NSNull objects in an NSDictionary
  23. Broadcast to Icecast / SHOUTcast with Objective-C, C, or C++
  24. Reason to use ivars vs properties in objective c
  25. Custom nav bar styling – iOS [duplicate]
  26. how to remove subviews from scrollview?
  27. Objective C: How to create a multi-line UITextField? [duplicate]
  28. symbol(s) not found for architecture armv6
  29. What is the difference between a __weak and a __block reference?
  30. Class method equivalent of -respondsToSelector:

Leave a Comment