Re: Problem implementing keyPathsForvaluesAffecting<Key>
Re: Problem implementing keyPathsForvaluesAffecting<Key>
- Subject: Re: Problem implementing keyPathsForvaluesAffecting<Key>
- From: Jim Correia <email@hidden>
- Date: Thu, 23 Apr 2009 18:21:40 -0400
On Apr 22, 2009, at 10:45 AM, email@hidden wrote:
The property canDelete is dependent on three other properties as
shown below.
Is there a problem with my implementation of +
keyPathsForValuesAffectingCanDelete with regard to the key path
@"arrayController.canRemove"?
Is is a relatively well known issue that NSKeyValueObservingOptionNew
and NSKeyValueObservingOptionOld do not work with controller
properties. See:
http://homepage.mac.com/mmalc/CocoaExamples/controllers.html
What is perhaps less well known is that controller keys which don't
support the New/Old KVO observing options also don't support
NSKeyValueObservingOptionPrior.
The +keyPathsForValuesAffecting<Key> mechanism relies on
NSKeyValueObservingOptionPrior in order to do its magic.
Until such time as controller keys correctly support the KVO observing
options, you can't
a) rely on Old/New/Prior in your own observers
b) use a controller property as part of a key path in
+keyPathsForValuesAffecting<Key>
- Jim
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