I'm using KVO as a generalized recalculation engine, somewhat akin to how a spreadsheet recalcuates values based on what's changed. It's mostly successful once you eliminate cycles, but there is a persistent problem.
On each relevant object, I have a observeValueForKeyPath:ofObject:change:context: method which then triggers willChangeValueForKey: / didChangeValueForKey: for dependent properties. I've noticed that when observeValueForKeyPath:ofObject:change:context gets called more than once in a row for an object, one of the other observed objects dies in didChangeValueForKey: -- here's the stack trace Program received signal: “EXC_BAD_ACCESS”. #0 0x7fff84d31ae1 in NSKVOPendingNotificationRelease #1 0x7fff88aa0bd3 in __CFArrayReleaseValues #2 0x7fff88a815f8 in _CFArrayReplaceValues #3 0x7fff84d31e35 in NSKeyValuePopPendingNotificationPerThread #4 0x7fff84d31dca in NSKeyValueDidChange #5 0x7fff84d1574f in -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] #6 0x1000181c8 in -[CMEdge didChangeValueOnceForKey:] at CMEdge.m:133 #7 0x100019f51 in -[CMNode observeValueForKeyPath:ofObject:change:context:] at CMNode.m:222 The only workaround is to perform the didChangeValueForKey: in the next event cycle i.e. by using performSelectorOnMainThread:withObject:waitUntilDone: Not really ideal especially since I'm worried I'm just covering up the root of the problem, whatever it is. Any ideas on the cause? Side question: I can of course use keyPathsForValuesAffectingValueForKey: and friends to declare the dependencies instead of using a procedure to react to them, but I need to execute code as well e.g. update the observed value. For example, say A = B/C. When either B or C changes, you want A to change too. I can use keyPathsForValuesAffectingA to declare it depends on B or C, but I need to update the cached A value whenever B or C changes -- how would I do that without using observeValueForKeyPath:ofObject:change:context:? Cheers Glen Low Pixelglow Software_______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) 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 arch...@mail-archive.com
