A Self observing button with badge

//
class CartButtonView: UIButton {
    let image = #imageLiteral(resourceName: "cart")
    var count:NSString = "0"
    
    override init(frame: CGRect) {
        super.init(frame: frame)
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    
    func updateCount(notification:Notification) {
        if let count = notification.object as? String {
            self.count = count as NSString
            self.setNeedsDisplay()
        }
    }
    
    func registerObserver()  {
         NotificationCenter.default.addObserver(self, selector: #selector(updateCount), name: NSNotification.Name(rawValue: "updateCount"), object: nil)
    }
    
    func unregisterObserver()  {
        NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: "updateCount"), object: count)
    }
    
    deinit {
        unregisterObserver()
    }
    
    
    override func willMove(toSuperview newSuperview: UIView?) {
        if newSuperview == nil {
            unregisterObserver()
        }else {
            registerObserver()
        }
    }
    
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        // obtain context
        let ctx = UIGraphicsGetCurrentContext()
        // make insets before drawing image
        let newRect = CGRect(x: 2, y: 10, width: self.frame.width - 10, height: self.frame.height - 10)
        //ctx?.draw(image.cgImage!, in: newRect)
        image.draw(in: newRect)
        // decide on radius
        var circleRect = CGRect(x:self.frame.width - 20 , y: 2, width: 20, height: 20)
        let circleCenter = CGPoint(x: self.frame.width - circleRect.width/2.0 , y: circleRect.width/2.0)
        
        let rad = CGFloat(10)
        let endAngle = CGFloat(2 * Double.pi)
        // add the circle to the context
        ctx?.addArc(center: circleCenter, radius: rad, startAngle: 0, endAngle: endAngle, clockwise: true)
        // set fill color
        ctx?.setFillColor(UIColor.red.cgColor)
        // set stroke color
        ctx?.setStrokeColor(UIColor.white.cgColor)
        // set line width
        ctx?.setLineWidth(0.0)
        // draw the path
        ctx?.drawPath(using: .fillStroke)
        
        let textFont = UIFont(name: "Lato" , size: 12)
        let textFontAttributes = [
            NSFontAttributeName: textFont!,
            NSForegroundColorAttributeName: UIColor.white,
            
            ] as [String : Any]
        let size = count.size(attributes: textFontAttributes)
        let diff = circleRect.width - size.width
        circleRect.origin.x = circleRect.origin.x + diff/2.0
        count.draw(in: circleRect, withAttributes: textFontAttributes)
        //ctx?.closePath()
    }
}