iOS去掉导航栏下方的横线

在viewWillAppear 方法中敲以下代码：

- (void)viewWillAippear:(BOOL)animated {
    [super viewWillAppear:animated];

    //去除导航栏下方的横线
    [self.navigationController.navigationBar setBackgroundImage:[[UIImage alloc] init]
        forBarMetrics:UIBarMetricsDefault];
    [self.navigationController.navigationBar setShadowImage:[[UIImage alloc] init]];
}