Swift 5 CAKeyframeAnimation - Resume layer animation after app moved to bacground - ios

Question

I have view to display small indicator bars (for sound)
and here it is code for this:
class IndicatorView: UIViewController {
enum AudioState {
case stop
case play
case pause
}
var state: AudioState! {
didSet {
switch state {
case .pause:
pauseAnimation()
case .play:
playAnimation()
default:
stopAnimation()
}
}
}
var numberOfBars: Int = 5
var barWidth: CGFloat = 4
var barSpacer: CGFloat = 4
var barColor: UIColor = .systemPink
private var bars: [UIView] = [UIView]()
private func stopAnimation() {
bars.forEach { $0.alpha = 0 }
}
private func pauseAnimation() {
bars.forEach {
$0.layer.speed = 0
$0.transform = CGAffineTransform(scaleX: 1, y: 0.1)
}
}
private func playAnimation() {
bars.forEach {
$0.alpha = 1
$0.layer.speed = 1
}
}
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .clear
DispatchQueue.main.async {
self.setupViews()
}
}
private func setupViews() {
for i in 0...numberOfBars - 1 {
let b = UIView()
b.backgroundColor = barColor
addAnimation(to: b)
view.addSubview(b)
bars.append(b)
b.anchor(top: view.topAnchor, leading: view.leadingAnchor, bottom: view.bottomAnchor, trailing: nil,
padding: .init(top: 0, left: CGFloat(i) * (barWidth + barSpacer), bottom: 0, right: 0),
size: .init(width: barWidth, height: 0))
}
stopAnimation()
}
private func addAnimation(to v: UIView) {
let animation = CAKeyframeAnimation()
animation.keyPath = "transform.scale.y"
animation.values = [0.1, 0.3, 0.2, 0.5, 0.8, 0.3, 0.99, 0.72, 0.3].shuffled()
animation.duration = 1
animation.autoreverses = true
animation.repeatCount = .infinity
v.layer.add(animation, forKey: "baran")
}
}
and work fine. I'm using it from another vc..etc.
Problem
When app moved to background, music player paused, and in IndicatorView state = .pause is assigned, but when app come back, and user tap on play eg. in IndicatorView state = .play
playAnimation() is called, bars layers have speed one... but no animation at all.
Here is a short video to describe my problem
Thanks

Answer 1

When the app goes to background the CALayer animation is paused. You could implement methods to pause and resume animation when going to bg/fg, but for your case if you move the call to "addAnimation(to: b)" from the setupviews to the "playAnimation()" method, you can guarantee the animation will always be there. ex:
bars.forEach {
$0.alpha = 1
addAnimation(to: $0)
$0.layer.speed = 1
}
Hope it helps :)