Implicit animation on CALayer “contents” property

Question

According to the core animation documentation, setting the layer contents should trigger an implicit 0.25 animation that will transition between the new and old images. I also see many places where people are asking how to remove this implicit animation but for some reason when I try this on my project, I get an instant swap of images. Reading some more into the documention I saw this code snipped:

- (id<CAAction>)actionForLayer:(CALayer *)theLayer
                        forKey:(NSString *)theKey {
    CATransition *theAnimation=nil;

    if ([theKey isEqualToString:@"contents"]) {

        theAnimation = [[CATransition alloc] init];
        theAnimation.duration = 1.0;
        theAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
        theAnimation.type = kCATransitionPush;
        theAnimation.subtype = kCATransitionFromRight;
    }
    return theAnimation;
}

Which implies that "contents" is not implicitly animated.

I would be very interested to understand this better.

Answer 1

OK, I'm copying some code from an app of mine. First I usually get CATransition not with alloc..init.. but using +animation. Second I'm not seeing that you are adding the transition to a layer. Third I'm not sure that CATransition are implicitly animated, CALayer properties yes.

CATransition *transition = [CATransition animation];
    transition.duration = 1;
    transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    transition.type = kCATransitionPush;
    transition.subtype = slideCATransitionCompareTable[ arc4random() % 4]; //to get a random subtype 
    [self.slideShowReceiptImageView.layer addAnimation:transition forKey:nil];