Solving the problem of CALayer animations being removed when application goes to background

CALayer+Pause.swift

//
//  CALayer+Pause.swift
//
//  Created by Grzegorz Krukowski on 11/05/2017.
//  Copyright © 2017. All rights reserved.
//

import Foundation

extension CALayer {
    func pause() {
        if self.isPaused() == false {
            let pausedTime: CFTimeInterval = self.convertTime(CACurrentMediaTime(), from: nil)
            self.speed = 0.0
            self.timeOffset = pausedTime
        }
    }

    func isPaused() -> Bool {
        return self.speed == 0.0
    }

    func resume() {
        let pausedTime: CFTimeInterval = self.timeOffset
        self.speed = 1.0
        self.timeOffset = 0.0
        self.beginTime = 0.0
        let timeSincePause: CFTimeInterval = self.convertTime(CACurrentMediaTime(), from: nil) - pausedTime
        self.beginTime = timeSincePause
    }
}

ViewWithPersistentAnimations.swift

//
//  ViewWithPersistentAnimations.swift
//
//  Created by Grzegorz Krukowski on 12/05/2017.
//  Copyright © 2017. All rights reserved.
//

/* Solving the problem of CALayers animations being lost when application is going to background */

import Foundation

class ViewWithPersistentAnimations : UIView {
    private var persistentAnimations: [String: CAAnimation] = [:]
    private var persistentSpeed: Float = 0.0

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.commonInit()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.commonInit()
    }

    func commonInit() {
        NotificationCenter.default.addObserver(self, selector: #selector(didBecomeActive), name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(willResignActive), name: NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
    }

    deinit {
        NotificationCenter.default.removeObserver(self)
    }

    func didBecomeActive() {
        self.restoreAnimations(withKeys: Array(self.persistentAnimations.keys))
        self.persistentAnimations.removeAll()
        if self.persistentSpeed == 1.0 { //if layer was plaiyng before backgorund, resume it
            self.layer.resume()
        }
    }

    func willResignActive() {
        self.persistentSpeed = self.layer.speed

        self.layer.speed = 1.0 //in case layer was paused from outside, set speed to 1.0 to get all animations
        self.persistAnimations(withKeys: self.layer.animationKeys())
        self.layer.speed = self.persistentSpeed //restore original speed

        self.layer.pause()
    }

    func persistAnimations(withKeys: [String]?) {
        withKeys?.forEach({ (key) in
            if let animation = self.layer.animation(forKey: key) {
                self.persistentAnimations[key] = animation
            }
        })
    }

    func restoreAnimations(withKeys: [String]?) {
        withKeys?.forEach { key in
            if let persistentAnimation = self.persistentAnimations[key] {
                self.layer.add(persistentAnimation, forKey: key)
            }
        }
    }
}

can u update it to swift 4