LKTextDidChangeAction.swift

class LKTextDidChangeAction : CAAnimationGroup {
    /// Here interpolation context gets stored
    @objc var interpolatedAttributeStates : NSMutableDictionary!
    
    var fromAttributedText : NSAttributedString?
    var toAttributedText : NSAttributedString?
    
     required override init() {
        super.init()
    }
    
    required init(from text: NSAttributedString?) {
        super.init()
        fromAttributedText = text
        interpolatedAttributeStates = type(of: self).stringAttributesDictionary
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func run(forKey event: String, 
                   object anObject: Any, 
                    arguments dict: [AnyHashable : Any]?) {
        guard let textLayer = anObject as? LKLabelLayer, 
                  event == keyPath(\LKLabelLayer.attributedText) else { return }

        self.toAttributedText = textLayer.attributedText
    }
}