How to identify CAAnimation within the animationDidStop delegate?

Question

I had a problem where I had a series of overlapping CATransition / CAAnimation sequences, all of which I needed to perform custom operations when the animations stopped, but

Answer 1

I can see mostly objc answers I will make one for swift 2.3 based on the best answer above.

For a start it will be good to store all those keys on a private struct so it is type safe and changing it in the future won't bring you annoying bugs just because you forgot to change it everywhere in the code:

private struct AnimationKeys {
    static let animationType = "animationType"
    static let volumeControl = "volumeControl"
    static let throbUp = "throbUp"
}

As you can see I have changed the names of the variables/animations so it is more clear. Now setting these keys when the animation is created.

volumeControlAnimation.setValue(AnimationKeys.volumeControl, forKey: AnimationKeys.animationType)

(...)

throbUpAnimation.setValue(AnimationKeys.throbUp, forKey: AnimationKeys.animationType)

Then finally handling the delegate for when the animation stops

override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
    if let value = anim.valueForKey(AnimationKeys.animationType) as? String {
        if value == AnimationKeys.volumeControl {
            //Do volumeControl handling
        } else if value == AnimationKeys.throbUp {
            //Do throbUp handling
        }
    }
}