导航底部黑线去掉

UINavigationBar *navigationBar = self.navigationController.navigationBar;
    // white.png图片自己下载个纯白色的色块，或者自己ps做一个
    [navigationBar setBackgroundImage:[UIImage imageNamed:@"nav2"]
                       forBarPosition:UIBarPositionAny
                           barMetrics:UIBarMetricsDefault];
    [navigationBar setShadowImage:[UIImage new]];