On Jul 2, 2008, at 3:16 AM, Ken Thomases wrote:
As a model object, NSMutableDictionary is somewhat problematic. It
is only KVO-compliant if it is modified with setValue:forKey:. Any
change made via setObject:forKey:, the NSMutableDictionary primitive
method, is not broadcast to observers.
There I go again, spreading misinformation. *sigh*
I had thought that most NSMutableDictionary methods were not KVO-
compliant, but I just ran some tests. They all are! (At least, on
Leopard.)
That said, much of what I had said still applies:
*) Exposing an NSMutableDictionary as part of your model violates
encapsulation. Yes, you can get KVO notifications of changes to it,
but you can't act as a gatekeeper for such changes.
*) It's not possible to observe an NSMutableDictionary for the
addition of new keys. You either have to know the keys in advance or
observe the set of keys that the dictionary has at a given point in
time.
*) If you want to observe all of the keys of a dictionary, you either
have to add the observer for each key individually or wrap the
dictionary in a class where you can implement a synthetic property
like the "anyPreferences" that I suggested. Put another way, you
can't set up dependent keys without a custom class. (Hrmm. A
category on NSMutableDictionary could provide a
+keyPathsForValuesAffecting<Key> method, but wow is that a bad idea.)
Cheers,
Ken
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