CABaseAnimation Delegate - ios

Question

I used CABaseAnimation to create layer's animation,and set CABaseAnimation's delegate to viewController, here is code:
let flyRight = CABasicAnimation(keyPath: "position.x")
flyRight.delegate = self
flyRight.toValue = view.bounds.size.width/2
flyRight.fromValue = -view.bounds.size.width/2
flyRight.fillMode = kCAFillModeBoth
flyRight.duration = 0.5
flyRight.setValue(heading.layer, forKey: "heading")
heading.layer.addAnimation(flyRight, forKey: nil)
flyRight.beginTime = CACurrentMediaTime() + 0.3
flyRight.setValue(username.layer, forKey: "username")
username.layer.addAnimation(flyRight, forKey: nil)
username.layer.position.x = view.bounds.size.width/2
flyRight.beginTime = CACurrentMediaTime() + 0.4
flyRight.setValue(password.layer, forKey: "password")
password.layer.addAnimation(flyRight, forKey: nil)
password.layer.position.x = view.bounds.size.width/2
the delegate animationDidStop method code is as follows:
override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
print(anim)
if let layer = anim.valueForKey("heading") as? CALayer {
anim.setValue(nil, forKey: "heading")
let animation = CABasicAnimation(keyPath: "transform.scale")
animation.fromValue = 1.0
animation.toValue = 1.5
animation.duration = 1.0
layer.addAnimation(animation, forKey: nil)
print("heading layer animation did stop")
}
}
but in the delegate method I found that the console prints three times "heading layer animation did stop", here is the print line in console:
<CABasicAnimation: 0x7fbe13096b10>
heading layer animation did stop
<CABasicAnimation: 0x7fbe13020bf0>
heading layer animation did stop
<CABasicAnimation: 0x7fbe13096c80>
heading layer animation did stop
I'm very confused as to why the print method executed three times.

Answer 1

Your code says (in essence):
flyRight.delegate = self
flyRight.setValue(heading.layer, forKey: "heading")
heading.layer.addAnimation(flyRight, forKey: nil)
username.layer.addAnimation(flyRight, forKey: nil)
password.layer.addAnimation(flyRight, forKey: nil)
So you are adding this animation to three different layers. Before you did that, you set its "heading" key to heading.layer, and you set the animation's delegate to self. Thus, we have three layers running an animation where delegate is self and where the "heading" key is heading.layer.
So now we come to your animationDidStop handler:
override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
if let layer = anim.valueForKey("heading") as? CALayer {
print(/*...*/)
}
}
So all three animations end up calling the animationDidStop handler, and in all three animations the if let layer test passes; all three of them do indeed have a key "heading" which is a CALayer. Hence, all three times you see the printout. It's obvious.
(Indeed, the only thing that is not obvious is why you are surprised. The only explanation I can think of is that you don't realize that addAnimation:forKey: adds a copy of the animation. That is something that some people do not realize. But it is hard to see why not realizing that would cause your surprise in this particular situation.)