//去掉导航栏下面的线  oc
    [self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"white_bg"] forBarMetrics:UIBarMetricsDefault];
    [self.navigationController.navigationBar setShadowImage:[UIImage new]];
 
      //去掉导航栏下面的线  swift
        self.navigationController?.navigationBar.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
        self.navigationController?.navigationBar.shadowImage = UIImage()