Classic slide to unlock animation swift implemntation

ViewController.swift

//
//  ViewController.swift
//  GradientAnimation
//
//  Created by Henry Lee on 2019/11/19.
//  Copyright © 2019 Henry Lee. All rights reserved.
//

import UIKit

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let height:CGFloat = 30.0
        
        let someView:UIView = UIView(frame: CGRect(x: 0, y: (view.frame.height-height)/2.0,
                                                   width: view.frame.width, height: height))
        
        let gradientLayer:CAGradientLayer = CAGradientLayer()
        gradientLayer.colors = [UIColor.black.cgColor,UIColor.white.cgColor,UIColor.black.cgColor]
        gradientLayer.locations = [0.0,0.5,1.0]
        gradientLayer.type = .axial
        gradientLayer.startPoint = CGPoint(x:0.0,y:0.5)
        gradientLayer.endPoint = CGPoint(x:1.0,y:0.5)
        gradientLayer.frame = CGRect(x: -someView.bounds.width, y: someView.bounds.minY,
                                     width: someView.bounds.width*3, height: someView.bounds.height)
        someView.layer.addSublayer(gradientLayer)
        someView.layer.masksToBounds = true
        
        let gradientAnimation = CABasicAnimation(keyPath: "locations")
        gradientAnimation.fromValue = [0.0,0.0,0.25]
        gradientAnimation.toValue = [0.75,1.0,1.0]
        gradientAnimation.duration = 3.0
        gradientAnimation.repeatCount = Float.infinity
        gradientLayer.add(gradientAnimation, forKey: nil)
        
        let textAttributes: [NSAttributedString.Key: Any] = {
          let style = NSMutableParagraphStyle()
          style.alignment = .center
          return [
            NSAttributedString.Key.font: UIFont(
              name: "HelveticaNeue-Thin",
              size: 28.0)!,
            NSAttributedString.Key.paragraphStyle: style
          ]
        }()
        
        let image = UIGraphicsImageRenderer(size: someView.bounds.size)
          .image { _ in
            "Slide to unlock".draw(in: someView.bounds, withAttributes: textAttributes)
        }
        
        let maskLayer = CALayer()
        maskLayer.backgroundColor = UIColor.clear.cgColor
        maskLayer.frame = someView.bounds.offsetBy(dx: someView.bounds.size.width, dy: 0)
        maskLayer.contents = image.cgImage
        
        gradientLayer.mask = maskLayer
        
        self.view.addSubview(someView)
    }
}

Effect: