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

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 :)