I'm a bit confused about KVO in Objective-C. If my property is KVO-compliant, do I have two choices to emit the notification: 1. addObserver:.../observeValueForKeyPath:...and 2.did/willChangeValueForKey..., or should we use the methods did/willChangeValueForKey in a particular context?
I noticed that the second one (did...) can be used to group a number of changes into a single notification; are there other important things to understand about those two ways? Is the first method (addObserver:...) impossible to use in some contexts (although the context would be KVO-compliant)?
edit:
in a subclass of NSManagedObject, only did/willChangeValueForKey... were used, but not addObserver:.../observeValueForKeyPath:... : do you know why?
Those two pairs are used by the two sides to the KVO interaction; they are not at all interchangeable.
addObserver:forKeyPath:options:context: and observeValueForKeyPath:ofObject:change:context: are used by the client, the one who wants to do the observing.
observeValueForKeyPath:ofObject:change:context: is essentially a callback; it will be sent by the internal KVO mechanisms when the observed ("provider") object uses the other set of methods (the various did/will changeValueFor...). The notification is actually made at that time, by the change methods.