Core Animation - modify animation property - ios

Question

I have animation
func startRotate360() {
let rotation : CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
rotation.fromValue = 0
rotation.toValue = Double.pi * 2
rotation.duration = 1
rotation.isCumulative = true
rotation.repeatCount = Float.greatestFiniteMagnitude
self.layer.add(rotation, forKey: "rotationAnimation")
}
What I want is ability to stop animation by setting its repeat count to 1, so it completes current rotation (simply remove animation is not ok because it looks not good)
I try following
func stopRotate360() {
self.layer.animation(forKey: "rotationAnimation")?.repeatCount = 1
}
But I get crash and in console
attempting to modify read-only animation
How to access writable properties ?

Answer 1

Give this a go. You can in fact change CAAnimations that are in progress. There are so many ways. This is the fastest/simplest. You could even stop the animation completely and resume it without the user even noticing.
You can see the start animation function along with the stop. The start animation looks similar to yours while the stop grabs the current rotation from the presentation layer and creates an animation to rotate until complete. I also smoothed out the duration to be a percentage of the time needed to complete based on current rotation z to full rotation based on the running animation. Then I remove the animation with the repeat count and add the new animation. You can see the view rotate smoothly to the final position and stop. You will get the idea. Drop it in and run it and see what you think. Hit the button to start and hit it again to see it finish rotation and stop.
import UIKit
class ViewController: UIViewController {
var animationView = UIView()
var button = UIButton()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
animationView = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
animationView.backgroundColor = .green
animationView.center = view.center
self.view.addSubview(animationView)
let label = UILabel(frame: animationView.bounds)
label.text = "I Spin"
animationView.addSubview(label)
button = UIButton(frame: CGRect(x: 20, y: animationView.frame.maxY + 60, width: view.bounds.width - 40, height: 40))
button.setTitle("Animate", for: .normal)
button.setTitleColor(.blue, for: .normal)
button.addTarget(self, action: #selector(ViewController.pressed), for: .touchUpInside)
self.view.addSubview(button)
}
func pressed(){
if let title = button.titleLabel?.text{
let trans = CATransition()
trans.type = "rippleEffect"
trans.duration = 0.6
button.layer.add(trans, forKey: nil)
switch title {
case "Animate":
//perform animation
button.setTitle("Stop And Finish", for: .normal)
rotateAnimationRepeat()
break
default:
//stop and finish
button.setTitle("Animate", for: .normal)
stopAnimationAndFinish()
break
}
}
}
func rotateAnimationRepeat(){
//just to be sure because of how i did the project
animationView.layer.removeAllAnimations()
let rotation : CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
rotation.fromValue = 0
rotation.toValue = Double.pi * 2
rotation.duration = 0.5
rotation.repeatCount = Float.greatestFiniteMagnitude
//not doing cumlative
animationView.layer.add(rotation, forKey: "rotationAnimation")
}
func stopAnimationAndFinish(){
if let presentation = animationView.layer.presentation(){
if let currentRotation = presentation.value(forKeyPath: "transform.rotation.z") as? CGFloat{
var duration = 0.5
//smooth out duration for change
duration = Double((CGFloat(Double.pi * 2) - currentRotation))/(Double.pi * 2)
animationView.layer.removeAllAnimations()
let rotation : CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
rotation.fromValue = currentRotation
rotation.toValue = Double.pi * 2
rotation.duration = duration * 0.5
animationView.layer.add(rotation, forKey: "rotationAnimation")
}
}
}
}
Result:

Answer 2

2019 typical modern syntax
Setup the arc and the layer like this:
import Foundation
import UIKit
class RoundChaser: UIView {
private let lineThick: CGFloat = 10.0
private let beginFraction: CGFloat = 0.15
// where does the arc drawing begin?
// 0==top, .25==right, .5==bottom, .75==left
private lazy var arcPath: CGPath = {
let b = beginFraction * .pi * 2.0
return UIBezierPath(
arcCenter: bounds.centerOfCGRect(),
radius: bounds.width / 2.0 - lineThick / 2.0,
startAngle: .pi * -0.5 + b,
// recall that .pi * -0.5 is the "top"
endAngle: .pi * 1.5 + b,
clockwise: true
).cgPath
}()
private lazy var arcLayer: CAShapeLayer = {
let l = CAShapeLayer()
l.path = arcPath
l.fillColor = UIColor.clear.cgColor
l.strokeColor = UIColor.purple.cgColor
l.lineWidth = lineThick
l.lineCap = CAShapeLayerLineCap.round
l.strokeStart = 0
l.strokeEnd = 0
// if both are same, it is hidden. initially hidden
layer.addSublayer(l)
return l
}()
then initialization is this easy
open override func layoutSubviews() {
super.layoutSubviews()
arcLayer.frame = bounds
}
finally animation is easy
public func begin() {
CATransaction.begin()
let e : CABasicAnimation = CABasicAnimation(keyPath: "strokeEnd")
e.duration = 2.0
e.fromValue = 0
e.toValue = 1.0
// recall 0 will be our beginFraction, see above
e.repeatCount = .greatestFiniteMagnitude
self.arcLayer.add(e, forKey: nil)
CATransaction.commit()
}
}

Answer 3

Maybe this is not the best solution but it works, as you say you can not modify properties of the CABasicAnimation once is created, also we need to remove the rotation.repeatCount = Float.greatestFiniteMagnitude, if notCAAnimationDelegatemethodanimationDidStop` is never called, with this approach the animation can be stoped without any problems as you need
step 1: first declare a variable flag to mark as you need stop animation in your custom class
var needStop : Bool = false
step 2: add a method to stopAnimation after ends
func stopAnimation()
{
self.needStop = true
}
step 3: add a method to get your custom animation
func getRotate360Animation() ->CAAnimation{
let rotation : CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
rotation.fromValue = 0
rotation.toValue = Double.pi * 2
rotation.duration = 1
rotation.isCumulative = true
rotation.isRemovedOnCompletion = false
return rotation
}
step 4: Modify your startRotate360 func to use your getRotate360Animation() method
func startRotate360() {
let rotationAnimation = self.getRotate360Animation()
rotationAnimation.delegate = self
self.layer.add(rotationAnimation, forKey: "rotationAnimation")
}
step 5: Implement CAAnimationDelegate in your class
extension YOURCLASS : CAAnimationDelegate
{
func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
if(anim == self.layer?.animation(forKey: "rotationAnimation"))
{
self.layer?.removeAnimation(forKey: "rotationAnimation")
if(!self.needStop){
let animation = self.getRotate360Animation()
animation.delegate = self
self.layer?.add(animation, forKey: "rotationAnimation")
}
}
}
}
This works and was tested
Hope this helps you