On 30/08/2009, at 12:35 PM, Roland King wrote:
Now this I don't understand. If you enter your dealloc method with observers registered on yourself and do have a *safe* mechanism of ensuring they are completely removed before ending the dealloc routine (or calling [ super dealloc ] ) I don't see where the issue should lie. Can you point me to the note on that please too. I suppose if you did permit this you're sending a message to an object whilst it's being deallocated however the KVO registration methods are supplied by the NSObject superclass, who's dealloc method has not yet been called.
I believe the issue lies in the fact that an object that has KVO observers registered on it is not the object you think it is. It's in fact a sort of proxy for the "real" object that has been swizzled (you can see this in the debugger as the class will be KVONotifying_Whatever). When the last observer is removed it's swizzled back to the original class. The question would be just how possible/safe this would be to do in -dealloc.
Nevertheless, I think it's a moot point. Apple have decreed that removing observers in dealloc is too late; it flags a fairly stern warning about doing it - a warning that got much more strongly worded between 10.4 and 10.5. So whether or not there could be a way to do it in theory, in practice you have to find a way to do it some other way. Personally I found that once I grokked this (and it did take a while) it started to inform the design of other parts of my data model, in that knowing I planned to use KVO meant that I would build-in proper mechanisms for observing and de-observing at the right places in a legal fashion. As a result I went from finding KVO a pain in the butt to being one of the best things about Cocoa.
One way or another, I think Andreas has to re-jig his design. --Graham _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
