Re: Setting NSObjectController's to file's owner

FROM : Michael Babin
DATE : Thu May 15 17:59:15 2008

On May 15, 2008, at 9:53 AM, André Pang wrote:

> Hmm, I just created a small test application to try to reproduce 
> this problem and couldn't get the retain cycle to happen.  It's a 
> dead-simple document-based Cocoa application with a single 
> NSObjectController in the nib file, with a single text field binding 
> that was bound through the object controller to an ivar in the 
> file's owner.
>
> However, now the weird thing is that I call -[objectController 
> release] in the file's owner -dealloc (which I guess should be the 
> correct behaviour, since the object controller is declared as an 
> IBOutlet and is a top-level nib file object), I get into an infinite 
> "release cycle" loop.  Test program here, for those willing to lend 
> a hand:
>
>  http://algorithm.com.au/tmp/NSObjectControllerRetainCycleTest.zip
>
> Am I completely misunderstanding memory management of bindings/nib 
> files objects?


In the small test application, you added the NSObjectController to the 
document's nib file (MyDocument.xib). As MyDocument is a descendant of 
NSDocument and you did not override -[NSDocument 
makeWindowControllers], the default implementation creates an 
NSWindowController with the windowNibName and MyDocument as the file's 
owner.

<http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Classes/NSDocument_Class/Reference/Reference.html#//apple_ref/occ/instm/NSDocument/makeWindowControllers
>

Since the created NSWindowController actually loads the nib, it is 
responsible for (and performs) freeing all top-level objects in the 
nib file. Doing so yourself in MyDocument's dealloc method is 
unnecessary and leads to an over-release problem, as you have 
discovered.

See: <http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Classes/NSWindowController_Class/Reference/Reference.html#//apple_ref/doc/c_ref/NSWindowController
>, Overview.