有一个页面要实现透明NavigationBar，实现了之后发现一个奇怪的问题：第一次进入此页面显示透明NavigationBar正常，返回上一级页面再重新进入，NavigationBar的底部出现了一条大约1px的横线，怎么都消除不了。
用Reveal查了一下这个横线，是一个UIImageView，0.5px高度，第一次正常显示的时候center y坐标为63.75，所以显示正常；返回上一级页面时再重新进入，center y坐标为64.25，正好出现在NavigationBar的下面而没有被它覆盖。
猜测是因为要实现透明NavigationBar在其中加了一个64px高度的OverLay View影响了这条横线的位置。最后在这篇文章中找到了解决方法：
First – declare instance variable:
@implementation MyViewController {
UIImageView *navBarHairlineImageView;}
Then, in viewDidLoad do:
navBarHairlineImageView = [self findHairlineImageViewUnder:navigationBar];
Method which finds the image view we need:
- (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) {
return imageView;
}
}
return nil;}
And this will do the rest of magic:
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
navBarHairlineImageView.hidden = YES;}- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
navBarHairlineImageView.hidden = NO;}
Same method should also work for UISearchBar hairline.
原文：http://my.oschina.net/ioslighter/blog/411972