override func viewDidLoad() {
        super.viewDidLoad()

        self.navigationController?.navigationBar.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
        self.navigationController?.navigationBar.shadowImage = UIImage()
        self.navigationController?.navigationBar.backgroundColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.0)

}