I would like to know the correct way to implement a non-stored value
that is dependent on members of a collection.
I am setting up the object that holds the dependent value as an
observer of the individual members of the collection like this:
[theFrameModule addObserver:self forKeyPath:kOverallWidth
options:NSKeyValueObservingOptionNew context:NULL];
And I use the following to see when one of the items in the collection
has changed:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context
{
if ([keyPath isEqualToString:kOverallWidth]) {
NSLog(@"got notification that overallwidth changed: %@",
object);
}
}
This works just fine. I get notified of the changes to the members of
the collection.
But my question is this:
I want my dependent value to exist very simply as a method. I don't
need or want it to be an ivar of its object. So something like this:
-(NSInteger)overallWidth;
{
NSInteger overallWidthSubtotal = 0;
for ( SLFrameModule * theModule in [self frameModules] )
{
overallWidthSubtotal += [theModule overallWidth];
}
return overallWidthSubtotal;
}
My problem is that when I use overallWidth in a binding, the value
does not get updated. There is some "tickle" that is not occurring.
I have replaced my -overallWidth method above with an iVar, and that
does work, but I would rather have it exist solely as the method
above. Is there any way to put something in my -
observeValueForKeyPath: method that will tell the KVO system that
overallWidth would be a different value if checked?
Thank you
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