Memory Management Question in Objective C

Question

I have a tableviewcontroller where I populate some data from a sqlite db and for each row, I download a file from a http server and cache it locally. I cache it only when the "detailsview" is opened. And the detailsview responds back to this table through a delegate after the file download is complete.

But, when this tableview itself is popped out of the navicontroller., the call to delegate fails with a EXEC_BAD_ACCESS

I called [_delegate retain] in the setDelegate of the details view and everything works fine, but I'm not sure whether this will leak memory...

Could anyone advise?

Answer 1

Your delegate is getting released prematurely, and sending a message to an invalid object will call EXEC_BAD_ACCESS. Retaining it will fix the problem, but in general it's good practice to not have an object retain its delegate, as there is the potential for retain cycles, so you might need to rethink your structure. If you're releasing your delegate when the view is dealloc'ed, you need to remove it unless you're also retaining the delegate in setDelegate:.

Answer 2

Generally, delegates are not retained to avoid retain cycles. If the delegate may be released before you, then it is the responsibility of the delegate to clear your reference before it is finished being deallocated (eg in its dealloc).

However, if any property is set to "retain" or "copy", then you would retain/copy it in the setter (or use @synthesized setters which will do it for you), and release it in dealloc to avoid leaking. As said above though, that may lead to a retain cycle so that neither object ever gets deallocated.

I would suggest you turn on some memory debugging with environment variables NSZombieEnabled and NSAutoreleaseFreedObjectCheckEnabled and see if it tells you which object is being over released.