navagationbar不显示底部线

有时我们需要实现如下场景，  (1)在同一个界面中 显示与隐藏NavigationBar底部分割线  (2)当离开这个ViewController的时候，仍然需要显示底部分割线。  效果图如下所示：

图1

图2

(1)定义变量  UIImageView*navBarHairlineImageView;

(2)创建findHairlineImageViewUnder方法，并在viewDidLoad中调用  - (UIImageView*)findHairlineImageViewUnder:(UIView*)view {  if([view isKindOfClass:UIImageView.class] && view.bounds.size.height<=1.0) {  return(UIImageView*)view;  }  for(UIView*subview in view.subviews) {  UIImageView*imageView = [self findHairlineImageViewUnder:subview];  if(imageView) {  returnimageView;  }  }  return nil;  }

viewDidLoad中调用  navBarHairlineImageView= [self findHairlineImageViewUnder:self.navigationController.navigationBar];

(3)在viewWillAppear方法中隐藏该分割线  navBarHairlineImageView.hidden=YES;

(4)在viewWillDisappear方法中显示该分割线  navBarHairlineImageView.hidden=NO;