Objective-C: Property / instance variable in category

Question

As I cannot create a synthesized property in a Category in Objective-C, I do not know how to optimize the following code:

@interface MyClass (Variant)
@prope         


        

Answer 1

.h-file

@interface NSObject (LaserUnicorn)

@property (nonatomic, strong) LaserUnicorn *laserUnicorn;

@end

.m-file

#import 

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