Re: release sent to deallocated instance under ARC .. how?
Re: release sent to deallocated instance under ARC .. how?
- Subject: Re: release sent to deallocated instance under ARC .. how?
- From: Roland King <email@hidden>
- Date: Sun, 25 Dec 2011 07:42:48 +0800
Getter is pretty ordinary
-(id<RKTableViewDelegate>*)delegate
{
return _delegate;
}
So in this case A has a strong reference to B and is B's delegate, fairly common pattern. A is now being deallocated and as part of that the delegate relationship is being broken, one of two ways, either in A's dealloc it calls [ B setDelegate:nil ] or it just waits for B's dealloc which happens as part of its own and B cleans up any delegate. In this case A was actually calling it explicitly because I prefer things which set things up, to clean them up, I like to see the pairing, but either is fine. In the setter, or rather in a factored out method called in the setter, I had the
self.delegate == delegateArg
line. Indeed, as you say, the getter of delegate was causing the current value of delegate (which is still A at that point) to be re-retained (not self). There was no real good reason to have done that, using _delegate == delegateArg is just as good, doesn't call the getter and doesn't retain/autorelease the return value and if I hadn't factored the code out into another method, but left it in the setter, I would have used the iVar directly for that reason.
I'm assuming ARC adds the retain/autorelease to stop the return value of the getter being released before the caller gets it (section 3.2.3 of the ARC spec).
On Dec 25, 2011, at 2:19 AM, Matt Neuburg wrote:
> On Sat, 24 Dec 2011 13:35:07 +0800, Roland King <email@hidden> said:
> object being dealloced. This line of code
>>
>> return self.delegate == delegateArg
>>
>> caused self to get a retain/autorelease, resurrecting the object. The change to use the ivar directly fixed it
>
> Using the ivar directly is also a way of using self (saying "delegate" is just a way of saying "self->delegate), so it isn't the mention of self that's the problem; it's probably that the delegate property has a custom getter doing some weird stuff. If so, that's a thing to beware of; getting sneaky with accessors is a way to trip oneself up later... I'd examine that getter if I were you. m.
>
> --
> matt neuburg, phd = email@hidden, <http://www.apeth.net/matt/>
> A fool + a tool + an autorelease pool = cool!
> Programming iOS 4!
> http://www.apeth.net/matt/default.html#iosbook
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