Animation not stoping using UIView.animate - ios

Question

My code is using a simple loop animation that is not stopping after the 5 second duration. All I want to do is have a second button that stops the animation. As you can see in my code, circle.stopAnimating() has no effect.
class VET: UIViewController {
#IBOutlet weak var circle: UIImageView!
var duration = 5
#IBAction func start(_ sender: Any) {
UIView.animate(withDuration: TimeInterval(duration), delay: 0.5, options: [.repeat, .autoreverse, .curveEaseIn, .curveEaseOut], animations: { () -> Void in
let scale = CGAffineTransform(scaleX: 0.25, y: 0.25)
self.circle.transform = scale
print("animation")
}, completion: { _ in
//if finished { or (finished: Bool)
// if isAnimating {
if self.circle.isAnimating {
self.circle.stopAnimating()
print("is animating -- stop animating")
} else {
self.circle.startAnimating()
print("start animating")
}
})
}
#IBAction func stop() {
circle.stopAnimating()
}

Answer 1

startAnimating and stopAnimating for change images of imageview in some interval like GIF. Here you used animation block with repeat and the completion block will only get called when the animation is interrupted. For example it gets called when the app goes in the background and comes back to the foreground again.
To stop animation after some interval you have to call forcefully removeAllAnimations after that interval. Please refer following code:
#IBOutlet weak var circle: UIImageView!
var duration = 10
func start() {
UIView.animate(withDuration: TimeInterval(duration), delay: 0.5, options: [.repeat, .autoreverse, .curveEaseIn, .curveEaseOut], animations: { () -> Void in
let scale = CGAffineTransform(scaleX: 0.25, y: 0.25)
self.circle.transform = scale
DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(self.duration * 1000)) {
// Code
self.circle.layer.removeAllAnimations()
}
print("animation")
}, completion: { _ in
let scale = CGAffineTransform(scaleX: 1.0, y: 1.0)
self.circle.transform = scale
})
}

Answer 2

You are using wrong approach to use animations if you need more control over it.
Instead use UIViewPropertyAnimator
The alternate property animator initializer gives you back an animator object that you need to start:
let animator = UIViewPropertyAnimator(duration: duration, curve: .linear) {
self.redSquare.backgroundColor = .green
}
animator.startAnimation()
Similarly you can use for stopping animations related to the animator
animator.stopAnimation()