Re: KVO: Observing an aggregate property of a collection?
Re: KVO: Observing an aggregate property of a collection?
- Subject: Re: KVO: Observing an aggregate property of a collection?
- From: Chris Suter <email@hidden>
- Date: Fri, 11 Jul 2008 09:50:57 +1000
On 11/07/2008, at 7:46 AM, Jens Alfke wrote:
How do I set up key-value observing of an aggregate property over an
array, like a sum?
Say I have a Bulb class with a boolean "lit" property. I have an
NSArrayController with an array of Bulbs, being shown in a table
view. To compute the number of lit bulbs I can do:
- (unsigned) litCount {
return [_bulbArrayController valueForKeyPath:
@"email@hidden"];
}
Now if I want to display this count in my UI, I need to get
notifications of when it changes. But what keypath do I observe?
I've tried "email@hidden", and I
don't get any exceptions, but the observer never triggers when I
change the "lit" property of a bulb in the array.
I believe that should work without any problem so long as you're not
adding or removing elements from the array using addObject,
removeObject or any of the other primitives (you have to modify the
array in a different way if you want that to work). If you're simply
modifying the property of an existing element, I believe it should
work. Can you post a test case?
--Chris
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