This contains the useful extensions for the UINavigationBar

UINavigationBar+Extension.swift

extension UINavigationBar {
    func hideShadowImage() {
        self.shadowImage = UIImage()
        if self.barStyle != .black {
            self.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
        }
    }
}

// Here is the usage.
override func viewDidLoad() {
    super.viewDidLoad()
    self.navigationController?.navigationBar.hideShadowImage()
}