How to draw chart bar with animation in swift 4+

ChartBarViewController.swift

//
//  ChartBarViewController.swift
//
//  Created by Onur Işık on 12.04.2019.
//  Copyright © 2019 Onur Işık. All rights reserved.
//

import UIKit

class ChartBarViewController: UIViewController {

    
    var chartLineList: [NSLayoutConstraint] = []

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor(red:0.99, green:0.96, blue:1.00, alpha:1.0)
        
        setupChartView()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        self.perform(#selector(animateBars), with: nil, afterDelay: 1.0)
    }
    
    @objc fileprivate func animateBars() {
        chartLineList.forEach { (heightConstraint) in
            heightConstraint.isActive = true
        }
        
        UIView.animate(withDuration: 1.0, delay: 0,
                       usingSpringWithDamping: 1,
                       initialSpringVelocity: 1,
                       options: .curveEaseIn, animations: {
            self.view.layoutIfNeeded()
        }, completion: nil)
    }

    private func setupChartView() {
        
        let chartViewContainer = UIView()
        chartViewContainer.backgroundColor = .white
        chartViewContainer.layer.cornerRadius = 10
        chartViewContainer.layer.shadowColor = UIColor.darkGray.cgColor
        chartViewContainer.layer.shadowRadius = 10
        chartViewContainer.layer.shadowOffset = CGSize(width: 0, height: 0)
        chartViewContainer.layer.shadowOpacity = 0.3;
        chartViewContainer.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(chartViewContainer)
        
        let label = UILabel()
        label.font = UIFont.boldSystemFont(ofSize: 30)
        label.textColor = .darkGray
        label.text = "Focus Time"
        label.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(label)
        
        let chartBarStackView = UIStackView(arrangedSubviews: [])
        chartBarStackView.distribution = .fillEqually
        chartBarStackView.alignment = .fill
        chartBarStackView.axis = .horizontal
        chartBarStackView.spacing = 3
        chartBarStackView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(chartBarStackView)
        
        addChartLines(in: chartBarStackView)
        
        NSLayoutConstraint.activate([
            chartViewContainer.heightAnchor.constraint(equalToConstant: 270),
            chartViewContainer.widthAnchor.constraint(equalToConstant: 350),
            chartViewContainer.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            chartViewContainer.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            
            label.leadingAnchor.constraint(equalTo: chartViewContainer.leadingAnchor, constant: 8),
            label.topAnchor.constraint(equalTo: chartViewContainer.topAnchor, constant: 10),
            label.trailingAnchor.constraint(equalTo: chartViewContainer.trailingAnchor, constant: -8),
            label.heightAnchor.constraint(equalToConstant: 25),
            
            
            chartBarStackView.leadingAnchor.constraint(equalTo: chartViewContainer.leadingAnchor, constant: 8),
            chartBarStackView.topAnchor.constraint(equalTo: label.bottomAnchor, constant: 10),
            chartBarStackView.trailingAnchor.constraint(equalTo: chartViewContainer.trailingAnchor, constant: -8),
            chartBarStackView.bottomAnchor.constraint(equalTo: chartViewContainer.bottomAnchor, constant: -10)
        ])
    }
    
    private func addChartLines(in stackView: UIStackView) {
        createMockChartData().forEach { (chart) in
            
            let chartLineBackground = UIView()
            chartLineBackground.backgroundColor = UIColor.init(white: 0.93, alpha: 1)
            chartLineBackground.layer.cornerRadius = 5
            chartLineBackground.layer.masksToBounds = true
            stackView.addArrangedSubview(chartLineBackground)
            
            let chartLine = ChartLine()
            chartLine.chart = chart
            chartLine.layoutSubviews()
            chartLine.translatesAutoresizingMaskIntoConstraints = false
            chartLineBackground.addSubview(chartLine)
            
            NSLayoutConstraint.activate([
                chartLine.leadingAnchor.constraint(equalTo: chartLineBackground.leadingAnchor),
                chartLine.trailingAnchor.constraint(equalTo: chartLineBackground.trailingAnchor),
                chartLine.bottomAnchor.constraint(equalTo: chartLineBackground.bottomAnchor)
            ])
            
            chartLine.heightAnchor.constraint(equalTo: chartLineBackground.heightAnchor, multiplier: 0).isActive = true
            
            let heightConstraint = chartLine.heightAnchor.constraint(equalTo: chartLineBackground.heightAnchor, multiplier: chart.range)
            heightConstraint.isActive = false
            
            chartLineList.append(heightConstraint)
        }
    }
    
    private func createMockChartData() -> [Chart] {
        
        return [
            Chart(topColor: .red, bottomColor: .purple, range: 0.2),
            Chart(topColor: .red, bottomColor: .purple, range: 0.3),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
            Chart(topColor: .red, bottomColor: .purple, range: 0.5),
            Chart(topColor: .red, bottomColor: .purple, range: 0.3),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.9),
            Chart(topColor: .red, bottomColor: .purple, range: 0.6),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
            Chart(topColor: .red, bottomColor: .purple, range: 0.7),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
            Chart(topColor: .red, bottomColor: .purple, range: 0.7),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.6),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
            Chart(topColor: .red, bottomColor: .purple, range: 0.7),
            Chart(topColor: .red, bottomColor: .purple, range: 0.9),
            Chart(topColor: .red, bottomColor: .purple, range: 0.1),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.2),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.6),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
            Chart(topColor: .red, bottomColor: .purple, range: 0.7),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
            Chart(topColor: .red, bottomColor: .purple, range: 0.7),
            Chart(topColor: .red, bottomColor: .purple, range: 0.8),
            Chart(topColor: .red, bottomColor: .purple, range: 0.4),
        ]
    }
}

struct Chart {
    let topColor: UIColor!
    let bottomColor: UIColor!
    let range: CGFloat!
}

class ChartLine: UIView {
    
    var chart: Chart! {
        didSet {
            gradientLayer.colors = [chart.topColor.cgColor, chart.bottomColor.cgColor]
        }
    }
    
    let gradientLayer = CAGradientLayer()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        gradientLayer.colors = []
        gradientLayer.cornerRadius = 5
        gradientLayer.masksToBounds = true
        gradientLayer.locations = [0.0, 0.5]
        layer.addSublayer(gradientLayer)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        gradientLayer.frame = bounds
    }
}

How it's look? Screen shot