AnimateUISliderWithDisplayLink.swift

//
//  ViewController.swift
//  CountAnm
//
//  Created by Onur Işık on 19.11.2018.
//  Copyright © 2018 Onur Işık. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    var elapsedTime:Double = 0.0
    private var startValue: Double = 0.0
    private var endValue: Double = 1000
    private let animationDuration = 2.5
    private var animationStartDate: Date!
    
    
    @IBOutlet weak var slider: UISlider!
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    func startCountUp() {
        elapsedTime = 0.0
        animationStartDate = Date()
        // create displayLink & add it to the run-loop
        let displayLink = CADisplayLink(target: self, selector: #selector(handleCountUp))
        displayLink.add(to: .main, forMode: .default)
    }
    
    func startCountDown() {
        elapsedTime = 0.0
        animationStartDate = Date()
        // create displayLink & add it to the run-loop
        let displayLink = CADisplayLink(target: self, selector: #selector(handleCountDown))
        displayLink.add(to: .main, forMode: .default)
    }
    
    @objc fileprivate func handleCountUp(_ displayLink: CADisplayLink) {
        
        let now = Date()
        elapsedTime = now.timeIntervalSince(animationStartDate)
        
        if elapsedTime < animationDuration {
            let percentage = elapsedTime / animationDuration
            let value = percentage * (endValue - startValue)
            self.slider.setValue(Float(value / 1000), animated: true)
        } else {
            displayLink.invalidate()
            self.startCountDown()
        }
        
    }
    
    @objc fileprivate func handleCountDown(_ displayLink: CADisplayLink) {
        
        let now = Date()
        elapsedTime = now.timeIntervalSince(animationStartDate)
        
        if elapsedTime < animationDuration {
            let percentage = elapsedTime / animationDuration
            let value = percentage * (endValue - startValue)
            let sliderValue = self.slider.value - Float(value / 15000)
            self.slider.setValue(sliderValue, animated: true)
        } else {
            displayLink.invalidate()
        }
        
    }
    
    @IBAction func startPressed(_ sender: Any) {
        self.startCountUp()
    }
    
}