Re: Bindings: is there a better way to observe when an object changes?
Re: Bindings: is there a better way to observe when an object changes?
- Subject: Re: Bindings: is there a better way to observe when an object changes?
- From: mmalc crawford <email@hidden>
- Date: Mon, 10 Sep 2007 10:53:23 -0700
On Sep 10, 2007, at 10:34 AM, Simone Tellini wrote:
I've added an "hasChanged" attribute to the entity and made it
dependent on all the other keys, using -
setKeys:triggerChangeNotificationsForDependentKey:
Then I've bound the view instance to the entity object using the
"hasChanged" key path.
I don't like this solution very much, though (for instance, I need
to remember to update the hasChanged dependancies if I add/remove an
attribute). I tried searching all over the documentation/google for
a better way to solve this problem, but I couldn't find anything
useful.
Well, ultimately you'll have to propagate changes, so you'll have to
remember to update dependencies somewhere... Keeping them encapsulated
by a single property means that you only have to remember to update
them in one place (rather than, for example, updating the view code
each time you update the entity). This is in essence the strategy
illustrated in GraphicsBindings (<http://homepage.mac.com/mmalc/CocoaExamples/GraphicsBindings.zip
>) although it also makes explicit:
+ (NSSet *)keysForValuesAffectingDrawingBounds;
+ (NSSet *)keysForValuesAffectingDrawingContents;
mmalc
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