Re: KVO - Observing self from self

FROM : Joakim Danielson
DATE : Sun Jul 02 11:25:26 2006

Why don't you use setKeys:triggerChangeNotificationsForDependentKey: ?

http://developer.apple.com/documentation/Cocoa/Conceptual/
KeyValueObserving/index.html#//apple_ref/doc/uid/10000177i


Joakim

1 jul 2006 kl. 17.43 skrev Daniel Jalkut:

>
> I'm using KVO to observe a keypath relative to "self." For example, 
> I'm observing "myTree.apples" from an object with a keyed object 
> "myTree."
>
> This is very convenient because it means I don't have to carefully 
> manage the addObserver/removeObserver status as "myTree" changes. 
> But I've noticed that KVO, in an attempt to protect me from "bad 
> stuff" actually limits my ability to use this technique.
>
> In the object's "dealloc" method, it removes observation of itself. 
> This should have the effect of cleaning everything up, right? But 
> apparently KVO interferes much earlier - detecting my impending 
> dealloc and warning me about the fact that there is still an observer:
>

>> An instance 0x38f6a0 of class CueSpecifier is being deallocated 
>> while key value observers are still registered with it.  Break on 
>> _NSKVODeallocateLog to start debugging.

>
> What's worse, is it apparently then removes the observer for me, so 
> that when my responsible "self cleanup" occurs moments later, I see 
> this in the console:
>

>> Exception ignored while releasing an object in an autorelease 
>> pool: [<CueSpecifier 0x38f6a0> removeObserver:<CueSpecifier 
>> 0x38f6a0> forKeyPath:@"cueHandler.parameterMenuItems"] was sent to 
>> an object that has no observers.

>
> I guess this is tricky because KVO's watch-dogging is happening at 
> the sneaky isa-swizzling level.
>
> What are my options? Does anybody have a clean solution for 
> observing self keypaths from self? I could figure out some way to 
> manually remove observation before being dealloc'd, but at that 
> point the convenience factor pretty much disappears.
>
> Daniel
>
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