Change label text on right bar item swift 4 - ios

Question

I have created a common nevigation method in view controller extension to show back, close and cart item on navigation bar through out my application. It shows the items on nav bar properly. But the cart item which is at the right side of the nav bar, has a button icon and a round badge icon with label. I need to update the label and increase the count on label every time an item is added in the cart. But somehow the label is not changing. Below is my code -
UIViewController Extension -
func setCartBarButtonItem() {
let cartBarButton = UIBarButtonItem.init(customView: getCartButton())
self.navigationItem.rightBarButtonItem = cartBarButton
}
func getCartButton() -> UIButton{
let frame = CGRect.init(x: UIScreen.main.bounds.width - 40, y: 14, width: 44, height:44)
let cartButton = UIButton.init(frame: frame)
cartButton.setImage(UIImage(named: "cart"), for: .normal)
cartButton.addTarget(self, action: #selector(self.cartButtonTapped), for: .touchUpInside)
let cartLabelView = UIView(frame: CGRect(x: cartButton.layer.bounds.width/2, y: 10, width: 16, height: 16))
cartLabelView.backgroundColor = UIColor(red: 255.0/255.0, green: 234.0/255.0, blue: 41.0/255.0, alpha: 1.0)
cartLabelView.layer.cornerRadius = 8
cartLabelView.layer.borderWidth = 0.5
cartLabelView.layer.borderColor = UIColor(red: 54.0/255.0, green: 54.0/255.0, blue: 54.0/255.0, alpha: 1.0).cgColor
cartButton.addSubview(cartLabelView)
let cartLabel = UILabel(frame: CGRect(x: cartLabelView.layer.bounds.width/3, y: 0, width: cartLabelView.layer.bounds.width, height: cartLabelView.layer.bounds.height))
cartLabel.textColor = UIColor.black
cartLabel.font = UIFont(name: "Arial", size: 9)
cartLabelView.addSubview(cartLabel)
cartLabelView.isHidden = true
var count = 0
count = getNumberOfItemInCart()
if count > 0 {
cartLabelView.isHidden = false
cartLabel.text = String(count)
}
return cartButton
}
In one delegate function which is called when item is added in cart, I call the this setCartBarButtonItem() to update the label. But label does not update. It shows the last value only.