swift-解决navigationcontroller底部线条

// 简单的很，就两句代码搞定
extension UINavigationController{
    
    func setSystemNavigationBarStyle(){
        self.navigationBar.setBackgroundImage(UIImage.imageWithColor(UIColor.white), for: UIBarMetrics.default)
        self.navigationBar.shadowImage = UIImage()
        self.navigationBar.tintColor = UIColor.black
    }
}