if #available(iOS 13.0, *) {
            let appearance = UINavigationBarAppearance()
            appearance.backgroundColor          = Colors.color_app
            appearance.titleTextAttributes      = [.foregroundColor : UIColor.white]
            appearance.largeTitleTextAttributes = [.foregroundColor : UIColor.white]
            appearance.shadowColor = .clear
            appearance.shadowImage = UIImage()
            
            UINavigationBar.appearance().tintColor            = .white
            UINavigationBar.appearance().standardAppearance   = appearance
            UINavigationBar.appearance().compactAppearance    = appearance
            UINavigationBar.appearance().scrollEdgeAppearance = appearance
        } else {
            UINavigationBar.appearance().barTintColor        = Colors.color_app
            UINavigationBar.appearance().tintColor           = .white
            UINavigationBar.appearance().titleTextAttributes = [NSAttributedString.Key.foregroundColor : UIColor.white]
            if #available(iOS 11.0, *) {
                UINavigationBar.appearance().largeTitleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.white]
            }
            UINavigationBar.appearance().isTranslucent = false
            
            UINavigationBar.appearance().shadowImage = UIImage()
            UINavigationBar.appearance().setBackgroundImage(UIImage(), for: .default)
        }

你应该在UISearchBar的底部添加一个视图

let rect = searchController.searchBar.frame;
let lineView : UIView = UIView.init(frame: CGRect.init(x: 0, y: rect.size.height-1, width: rect.size.width, height: 1))
lineView.backgroundColor = UIColor.init(hexString: "8CC73E")
searchController.searchBar.addSubview(lineView)

这可能听起来很愚蠢，但这个发际线只在viewController视图的背景色被设置为任何颜色时出现，除了白色。得知这个事实我很震惊。

如果你想让它毫不费力地消失只要设置控制器视图背景色为WHITE color。

对于iOS 9用户，这对我来说很有效。只要加上这个:

UINavigationBar.appearance().shadowImage = UIImage()

在AppDelegate中，这已经全局地改变了导航栏的格式:

 func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    UINavigationBar.appearance().setBackgroundImage(UIImage(), forBarPosition: UIBarPosition.Any, barMetrics: UIBarMetrics.Default)
    UINavigationBar.appearance().shadowImage = UIImage()
    UINavigationBar.appearance().tintColor = UIColor.whiteColor()
    UINavigationBar.appearance().barTintColor = UIColor.redColor()
    UINavigationBar.appearance().translucent = false
    UINavigationBar.appearance().clipsToBounds = false
    UINavigationBar.appearance().backgroundColor = UIColor.redColor()
    UINavigationBar.appearance().titleTextAttributes = [NSFontAttributeName : (UIFont(name: "FONT NAME", size: 18))!, NSForegroundColorAttributeName: UIColor.whiteColor()] }

还没有在特定的VC上实现任何不同的东西，但这将帮助90%的人

以上问题的答案

//删除1px的导航条线

[[UINavigationBar appearance] setBackgroundImage:[[UIImage alloc]init] forBarMetrics:UIBarMetricsDefault];
[[UINavigationBar appearance] setShadowImage:[[UIImage alloc] init]];
[[UINavigationBar appearance] setTranslucent:NO];
[[UINavigationBar appearance] setTintColor:[UIColor yourColor]];