how to put badge on UIBarButtonItem in swift 4?

I want put badge on UIBarButtonItem. for that I use the following reference

Add badge alert in right bar button item in swift

in this I create the 'UIBarButtonItem+Badge.swift' file and put that code in it. In my viewcontroller I take the outlet of the UIBarButtonItem. And call the function but it didn't work for me. my viewcontroller file is this

My UIBarButtonItem+Badge.swift file is

extension CAShapeLayer {
func drawRoundedRect(rect: CGRect, andColor color: UIColor, filled: Bool) {
    fillColor = filled ? color.cgColor : UIColor.white.cgColor
    strokeColor = color.cgColor
    path = UIBezierPath(roundedRect: rect, cornerRadius: 7).cgPath
   }
  }

   private var handle: UInt8 = 0;

   extension UIBarButtonItem {
private var badgeLayer: CAShapeLayer? {
    if let b: AnyObject = objc_getAssociatedObject(self, &handle) as AnyObject? {
        return b as? CAShapeLayer
    } else {
        return nil
    }
}

func setBadge(text: String?, withOffsetFromTopRight offset: CGPoint = CGPoint.zero, andColor color:UIColor = UIColor.red, andFilled filled: Bool = true, andFontSize fontSize: CGFloat = 11)
{
    badgeLayer?.removeFromSuperlayer()

    if (text == nil || text == "") {
        return
    }

    addBadge(text: text!, withOffset: offset, andColor: color, andFilled: filled)
}

 func addBadge(text: String, withOffset offset: CGPoint = CGPoint.zero, andColor color: UIColor = UIColor.red, andFilled filled: Bool = true, andFontSize fontSize: CGFloat = 11)
{
    guard let view = self.value(forKey: "view") as? UIView else { return }

    var font = UIFont.systemFont(ofSize: fontSize)

    if #available(iOS 9.0, *) { font = UIFont.monospacedDigitSystemFont(ofSize: fontSize, weight: UIFont.Weight.regular) }
    let badgeSize = text.size(withAttributes: [NSAttributedString.Key.font: font])

    // Initialize Badge
    let badge = CAShapeLayer()

    let height = badgeSize.height;
    var width = badgeSize.width + 2 /* padding */

    //make sure we have at least a circle
    if (width < height) {
        width = height
    }

    //x position is offset from right-hand side
    let x = view.frame.width - width + offset.x

    let badgeFrame = CGRect(origin: CGPoint(x: x, y: offset.y), size: CGSize(width: width, height: height))

    badge.drawRoundedRect(rect: badgeFrame, andColor: color, filled: filled)
    view.layer.addSublayer(badge)

    // Initialiaze Badge's label
    let label = CATextLayer()
    label.string = text
    label.alignmentMode = CATextLayerAlignmentMode.center
    label.font = font
    label.fontSize = font.pointSize

    label.frame = badgeFrame
    label.foregroundColor = filled ? UIColor.white.cgColor : color.cgColor
    label.backgroundColor = UIColor.clear.cgColor
    label.contentsScale = UIScreen.main.scale
    badge.addSublayer(label)

    // Save Badge as UIBarButtonItem property
    objc_setAssociatedObject(self, &handle, badge, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}

private func removeBadge() {
    badgeLayer?.removeFromSuperlayer()
   }
  }

my viewcontroller file is this

import UIKit

@IBOutlet weak var notificationLabel: UIBarButtonItem!

in view didload function

notificationLabel.addBadge(text: "4")

Here it is a simple solution for putting the badge on a navigation bar

let filterBtn = UIButton.init(frame: CGRect.init(x: 0, y: 0, width: 30, height: 30))
filterBtn.setImage(UIImage.fontAwesomeIcon(name: .filter, style: .solid,
                                                   textColor: UIColor.white,
                                                   size: CGSize(width: 25, height: 25)), for: .normal)
filterBtn.addTarget(self, action: #selector(filterTapped), for: .touchUpInside)

let lblBadge = UILabel.init(frame: CGRect.init(x: 20, y: 0, width: 15, height: 15))
self.lblBadge.backgroundColor = COLOR_GREEN
self.lblBadge.clipsToBounds = true
self.lblBadge.layer.cornerRadius = 7
self.lblBadge.textColor = UIColor.white
self.lblBadge.font = FontLatoRegular(s: 10)
self.lblBadge.textAlignment = .center

filterBtn.addSubview(self.lblBadge)

self.navigationItem.rightBarButtonItems = [UIBarButtonItem.init(customView: filterBtn)]

In your case

self.navigationItem.rightBarButtonItems = [notificationLabel.init(customView: filterBtn)]