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Re: ARC and NSObjectController bindings through file's owner
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Re: ARC and NSObjectController bindings through file's owner


  • Subject: Re: ARC and NSObjectController bindings through file's owner
  • From: Ken Thomases <email@hidden>
  • Date: Wed, 30 Jul 2014 15:45:04 -0500

On Jul 30, 2014, at 3:33 PM, Sean McBride <email@hidden> wrote:

> I'm slowing moving my GC app to ARC.  One runtime error I'm stuck at is:
>
> --------
> An instance 0x10f587510 of class MyDocument was deallocated while key value observers were still registered with it.
>
> <NSKeyValueObservance 0x107985ad0: Observer: 0x107985810, Key path: document.managedObjectContext, Options: <New: NO, Old: NO, Prior: NO> Context: 0x0, Property: 0x10ee1ac10>
> --------
>
> I have:
> - a nib who's File's Owner is an NSViewController subclass
> - an NSObjectController at the top-level of my nib
> - a strong IOOutlet from my NSViewController to the NSObjectController
> - the NSObjectController binds its 'managedObjectContext' binding to:
>   File's Owner.windowController.document.managedObjectContext
>
> It's something about that binding that's causing the trouble.  If I remove it, the error goes away.
>
> File's Owner (my NSViewController subclass) responds to 'windowController' because I have a vanilla synthesized weak property relating my NSViewController to its containing window's controller.
>
> It works under GC.  I just don't see how this is a problem under ARC... any one have any thoughts?

A zeroing weak property changes without emitting KVO change notifications.  Therefore, it's not KVO-compliant.  Basically, weak properties are incompatible with KVO and bindings.

Likewise, if any other property along that key path is changed in a non-KVO-compliant manner, that would lead to the same sort of error.

Regards,
Ken


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