iOS: Edit object inside a method - c++

Question

I am trying to edit an object inside a method like this:
-(void) createSprite:(CatSprite*) sprite{
UIImage *image = [UIImage imageNamed:BASE_SPRITE_IMAGE];
CGImageRef imageRef = image.CGImage;
sprite =[CatSprite spriteWithCGImage:imageRef key:nil];
}
and the call of the method like this:
[self createSprite:mySprite];
When debugging the method the object sprite is allocated, but after executing the method the object mySprite is null. Thank you.
PS: mySprite is an instance variable of type CatSprite (Extention from CCSprite).

Answer 1

First, I'm assuming you're using ARC. Second, you have two ways of doing this, though I'd recommend the first option...
Option 1
Return a new sprite, instead of trying to modify the caller's pointer:
- (CatSprite *)createSprite{
UIImage *image = [UIImage imageNamed:BASE_SPRITE_IMAGE];
CGImageRef imageRef = image.CGImage;
return [CatSprite spriteWithCGImage:imageRef key:nil];
}
You'd call this method using:
mySprite = [self createSprite];
Option 2
Pass a pointer to a pointer, and dereference:
- (void)createSpriteUsingSpritePointer:(CatSprite **)spritePointer{
UIImage *image = [UIImage imageNamed:BASE_SPRITE_IMAGE];
CGImageRef imageRef = image.CGImage;
*spritePointer = [CatSprite spriteWithCGImage:imageRef key:nil];
}
You'd call this method using:
[self createSprite:&mySprite];