隐藏导航栏下的黑线

//视图将要显示时隐藏

-(void)viewWillAppear:(BOOL)animated

{

[super viewWillAppear:animated];

[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];

[self.navigationController.navigationBar setShadowImage:[UIImage new]];

}

//视图将要消失时取消隐藏（一定要在willDisapear里面才行，在DidDisapear里面设置就没效果）

-(void)viewWillDisappear:(BOOL)animated

{

[super viewWillDisappear:animated];

[self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];

[self.navigationController.navigationBar setShadowImage:nil];

}