Demo for problem of animation sublayer with explicit animations

SublayerAnimationProblem.swift

import UIKit

class SublayerDelegate: NSObject, CALayerDelegate {
    
    func animationFromSuperlayer(of layer: CALayer, forKey event: String) -> CAAnimation? {
        guard let superlayer = layer.superlayer else { return nil }
        guard let firstAnimationKey = superlayer.animationKeys()?.first else { return nil }
        
        return superlayer.animation(forKey: event) ?? superlayer.animation(forKey: firstAnimationKey)
    }
    
    func action(for layer: CALayer, forKey event: String) -> (any CAAction)? {
        
        print("------- \(event)")
        layer.superlayer?.animationKeys()?.forEach({ print($0) })
        print("-------")
        
        if ["bounds", "position"].contains(event) {
            guard let superAnimation = animationFromSuperlayer(of: layer, forKey: event) else {
                return NSNull()
            }
            
            if let springAnimation = superAnimation as? CASpringAnimation {
                let animation = CASpringAnimation(perceptualDuration: springAnimation.perceptualDuration, bounce: springAnimation.bounce)
                // это не работает для относительных анимаций с isAdditive=true!
                animation.fromValue = layer.presentation()?.value(forKeyPath: event)
                return animation
            }
            let animation = CABasicAnimation(keyPath: event)
            // это не работает для относительных анимаций с isAdditive=true!
//            animation.fromValue = layer.presentation()?.value(forKeyPath: event)
            animation.duration = superAnimation.duration
            animation.timingFunction = superAnimation.timingFunction
            return animation
        }
        
        return NSNull()
    }
}

class MySublayer: CALayer {
    
    override init() {
        super.init()
        
        backgroundColor = UIColor.green.withAlphaComponent(0.5).cgColor
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override init(layer: Any) {
        super.init(layer: layer)
    }

    open override func add(_ anim: CAAnimation, forKey key: String?) {
        guard let key else { return }
        let mark: String.Element = "-"
        let fixedKey = if let endIndex = key.firstIndex(of: mark) {
            String(key[..<endIndex])
        } else {
            key
        }
        print("\(type(of: self)) | add animation: \(String(describing: key)), fixed: \(fixedKey)")
        super.add(anim, forKey: key)
    }
}

class MyLayer : CALayer {
    
    let sublayer = MySublayer()
    
    let sublayerDelegate = SublayerDelegate()
    
    override init() {
        super.init()
        
        backgroundColor = UIColor.blue.cgColor
            
        self.sublayer.delegate = sublayerDelegate
        self.addSublayer(self.sublayer)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override init(layer: Any) {
        super.init(layer: layer)
    }
    
    open override func add(_ anim: CAAnimation, forKey key: String?) {
        guard let key else { return }
        let mark: String.Element = "-"
        let fixedKey = if let endIndex = key.firstIndex(of: mark) {
            String(key[..<endIndex])
        } else {
            key
        }
        print("\(type(of: self)) | add animation: \(String(describing: key)), fixed: \(fixedKey)")
        if let basicAnimation = anim as? CABasicAnimation {
            let currentValue = self.presentation()?.value(forKeyPath: fixedKey)
            print("current state: \(String(describing: currentValue)), animation.fromValue: \(String(describing: basicAnimation.fromValue))")
        }
        super.add(anim, forKey: key)
//        super.add(anim, forKey: fixedKey)
    }
    
    override func layoutSublayers() {
        super.layoutSublayers()
        
        self.sublayer.bounds = .init(origin: .zero, size: bounds.size)
        self.sublayer.position = .init(x: bounds.midX, y: bounds.midY)
    }
}

class MyView : UIView {
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        self.backgroundColor = .red
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override class var layerClass: AnyClass {
        return MyLayer.self
    }
    
    func toggleSublayerHiddenState() {
        (self.layer as? MyLayer)?.sublayer.isHidden.toggle()
    }
}

class ViewController: UIViewController {
    
    var isBigButton: Bool = false {
        didSet {
            self.view.setNeedsLayout()
        }
    }
    
    let myView = MyView(frame: .init(origin: .zero, size: .init(width: 100, height: 100)))
    
    let myViewAnimateButton = UIButton(type: .system)
    
    let hideSublayerButton = UIButton(type: .system)
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.addSubview(myView)
        
        myViewAnimateButton.setTitle("Animate", for: .normal)
        myViewAnimateButton.addTarget(self, action: #selector(animate), for: .touchUpInside)
        myViewAnimateButton.sizeToFit()
        view.addSubview(myViewAnimateButton)
        
        hideSublayerButton.setTitle("Hide sublayer (green)", for: .normal)
        hideSublayerButton.addTarget(self, action: #selector(hideSublayer), for: .touchUpInside)
        hideSublayerButton.sizeToFit()
        view.addSubview(hideSublayerButton)
    }
    
    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        
        myView.bounds.size = isBigButton ? .init(width: 300, height: 300) : .init(width: 100, height: 100)
        myView.center = view.center
        
        myViewAnimateButton.center = .init(x: view.bounds.midX, y: view.bounds.maxY - 50)
        
        hideSublayerButton.center = .init(x: view.bounds.midX, y: view.bounds.maxY - 100)
    }
    
    @objc func animate() {
        UIView.animate(
            withDuration: 1,
            delay: 0,
//            usingSpringWithDamping: 1.0,
//            initialSpringVelocity: 0.0,
            options: [
//                .curveEaseInOut,
//                .beginFromCurrentState,
//                .layoutSubviews
            ],
        ) {
            self.isBigButton.toggle()
            self.view.layoutIfNeeded()
        }
    }
    
    @objc func hideSublayer() {
        myView.toggleSublayerHiddenState()
        UIView.animate(withDuration: 0.2) { [weak self] in
            guard let self else { return }
            self.hideSublayerButton.setTitle(self.myView.layer.sublayers?.first?.isHidden == false ? "Show sublayer (green)" : "Hide sublayer (green)", for: .normal)
            self.hideSublayerButton.sizeToFit()
            self.view.setNeedsLayout()
            self.view.layoutIfNeeded()
        }
    }
}