iOS 去除导航栏下的黑线

Swift:

navigationController?.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: .Default)
navigationController?.navigationBar.shadowImage = UIImage()

OC:

[self.navigationController.navigationBar setBackgroundImage:[[UIImage alloc] init] forBarMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setShadowImage:[[UIImage alloc] init]];