Re: KVO and the observeValueForKeyPath bottleneck

FROM : George Orthwein
DATE : Sat Jul 15 07:36:10 2006

Hi Matt,
Yeah I'm actually doing something similar though I wasn't aware of 
NSSelectorFromString.

For a custom view that responds to a few dozen attributes of the 
controller's current selection....

- (void)observeValueForKeyPath:(NSString *)keyPath
                     ofObject:(id)object
                        change:(NSDictionary *)change
                        context:(void *)context
{    
   NSString *keyPathName;
   if ([keyPath isEqualToString:@"selection.bgImage.color"] == YES){
       // handle special case of this attribute of a relationship
       keyPathName = @"bgImageColor";    
   } else {
       // convert "selection.attribute" keypath to appropriate accessor 
name -- by abusing pathExtension method :)
       keyPathName = [keyPath pathExtension];    
   }
   [self setValue:[object valueForKeyPath:keyPath] forKey:keyPathName];
}

So observing "selection.attribute" will call my setAttribute accessor 
with the new value via KVC.

Possibly not the most proper setup, but it seems to work well enough 
for this view's situation.

George