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I am trying to create a subclass of CALayer with a custom index property that I can both animate and change directly in order to display a different picture based on the index. In the header, I declared: @property NSUInteger index; In the implementation, I overrode needDisplayForKey : + (BOOL)needsDisplayForKey:(NSString *)key { if ([key isEqualToString:@"index"]) return YES; else return [super needsDisplayForKey:key]; } Now, in the display method, I want to display a picture based on the index. However, during an animation, the value of self.index never changes, so I have to query the value of the presentation layer, contrary to the example on Providing CALayer Content by Subclassing : - (void)display { NSUInteger presentationIndex = [(CustomLayer *)[self presentationLayer] index]; self.contents = (id)[[images objectAtIndex:presentationIndex] CGImage]; } The problem is, if I do that, I cannot set the index value directly outside of an animation, because it will only change the model layer, and the display method explicitly queries the presentation layer. If I add an initialization method that copies the value of index , it works: - (id)initWithLayer:(id)layer { self = [super initWithLayer:layer]; if (self) { if ([layer isKindOfClass:[CustomLayer class]]) self.index = [(CustomLayer *)layer index]; } return self; } However, after or before an animation, there is always a 1 image glitch because the presentation or the model value don't match (depending if I

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