Need to release a CGImage contained in a CALayer's contents property - ios

Question

I have a CALayer object called sublayer. I use it as self.sublayer throughout my view controller because I have made it a property in my view controller's header file.
I set the sublayer's contents property equal to a UIImage object that is created using a CGImageRef object called imageRef:
self.subLayer.contents = (id)[UIImage imageWithCGImage:imageRef].CGImage;
I then release the imageRef object right away now that it has been used to create the sublayer contents and it is no longer needed:
CGImageRelease(imageRef);
However, here is what is bothering me. Later on in the code I will no longer need self.sublayer.contents and I want to make sure I release the CGImage it contains properly.
If I NSLog self.sublayer.contents it will print this to the console: <CGImage 0x146537c0>
So I need to be able to release this CGImage as well.
I tried using this to release the CGImage, but the NSLog still prints the same to the console:
CGImageRelease((__bridge CGImageRef)(self.subLayer.contents));
If I use this, the NSLog will print to the console as (null), but I am worried that this is technically not releasing the CGImage:
self.subLayer.contents = nil;
Does setting the sublayer's contents property to nil properly release the CGImage, or am I correct in thinking that it is not technically releasing the CGImage?
I am experiencing memory problems right now in my app so I need to make sure that I am releasing this CGImage properly.

Answer 1

The contents property on CALayer is a retaining property, meaning that it's setter implementation more or less does this:
- (void)setContents:(id)contents
{
if (contents == _contents) return; // Same as existing value
[_contents release];
_contents = [contents retain];
}
So, when you set nil as the new contents, the old contents is released.