CALayer addSublayer increasing retain count?

Question

I think that when I add a view as a subview like such:

UIView* view = [[UIView alloc] init];
[self addSubview:view];
[view release];

that it's safe to release the view afterwards...is it the same for a CALayer object? If I create a CALayer using alloc/init, and do:

[self.layer addSublayer:layer];

is it safe to do a release of the layer afterwards?

Answer 1

Yes. In general if object A needs object B it is object A's responsibility to retain it. So if "self.layer" needs "layer, it will bump the retainCount during addSublayer: , and release layer when it is no longer needed. While there are some exceptions to this, those exceptions tend to be very well documented.

Answer 2

I agree with Louis. And although it's not really necessary in this case, note that you can always use the retainCount: method to double-check these things in the future. For example:

NSLog(@"Retain count before: %d", [layer retainCount]);
[self.layer addSublayer:layer];
NSLog(@"Retain count after: %d", [layer retainCount]);

Answer 3

First of all, you make a new CALayer object using the layer class method rather than alloc/init. Like so:-

CALayer *l = [CALayer layer];
l.frame = CGRectMake(...);
l.position = CGPointMake(...);
l.anchorpoint = CGPointMake(0,0);
l.contents = (id)someCGImageRef;
[self.layer addSublayer:l];

Secondly, this is where you can come unstuck because if you release the CALayer after adding it as a sublayer to your view's main layer, you'll get a crash. Or at least I did and I think it's because the layer class method adds the layer to the autorelease pool, so if you release it yourself you get a double-release and so it gets deallocated even thought he view's main layer is still using it.