Consecutive fade in fade out animations - ios

Question

I'm trying to implement this animation where a UIButton fades out when a user saves a file. While the button fades out, a UIImageView of a check mark image fades in place of the button. Once the imageview has fully faded in, then it fades out and the button fades back in.
UIView.animateWithDuration(0.60, delay: 0.0, options: UIViewAnimationOptions.CurveEaseOut, animations: {
self.recButton.alpha = 0.0
}, completion: {
(value: Bool) in
UIView.animateWithDuration(0.60, delay: 0.0, options: UIViewAnimationOptions.CurveEaseIn, animations: {
self.checkView.alpha = 1.0
}, completion: {
(value: Bool) in
UIView.animateWithDuration(0.60, delay: 0.0, options: UIViewAnimationOptions.CurveEaseOut, animations: {
self.checkView.alpha = 0.0
}, completion: {
(value: Bool) in
UIView.animateWithDuration(0.60, delay: 0.0, options: UIViewAnimationOptions.CurveEaseIn, animations: {
self.recButton.alpha = 1.0
self.recButton.enabled = true
}, completion: nil)
})
})
})
While the method above does work, its not as smooth as I would like. Is there a better way to go about this?

Answer 1

You need four keyframes for the animation you want: button fade out, image fade in, image fade out, button fade in.
let button: UIButton
let checkmarkImage: UIImageView
button.alpha = 1.0
checkmarkImage = 0.0
UIView.animateKeyframesWithDuration(2.4, delay: 0, options: .CalculationModeLinear, animations: {
UIView.addKeyframeWithRelativeStartTime(0.0, relativeDuration: 0.25, animations: {
button.alpha = 0.0
})
UIView.addKeyframeWithRelativeStartTime(0.25, relativeDuration: 0.25, animations: {
checkmarkImage.alpha = 1.0
})
UIView.addKeyframeWithRelativeStartTime(0.5, relativeDuration: 0.25, animations: {
checkmarkImage.alpha = 0.0
})
UIView.addKeyframeWithRelativeStartTime(0.75, relativeDuration: 0.25, animations: {
button.alpha = 1.0
})
}, completion: nil)
This question raised my curiosity - this keyframe thing is pretty cool.