设置导航栏背景色为透明
navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
隐藏导航栏下方的线条
navigationController?.navigationBar.shadowImage = UIImage()
设置导航栏的背景色
navigationController?.navigationBar.barTintColor = UIColor.white
设置导航栏背景不为半透明
navigationController?.navigationBar.isTranslucent = false