这两行代码对我总是非常有效:
navigationController?.navigationBar.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
navigationController?.navigationBar.shadowImage = UIImage()
如果你想要在全局范围内执行它,可以这样做:
UINavigationBar.appearance().shadowImage = UIImage()
UINavigationBar.appearance().setBackgroundImage(UIImage(), for: .default)