隐藏导航栏底部横线

@interface MyViewController {
UIImageView *navBarHairlineImageView;
}

// 加入下面的
- (void)viewDidLoad {
navBarHairlineImageView = [self findHairlineImageViewUnder:self.navigationController.navigationBar];
}

- (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;
}

// 在这里控制隐藏显示
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
navBarHairlineImageView.hidden = YES;
}

- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
navBarHairlineImageView.hidden = NO;
}

或者
UINavigationBar *navigationBar = self.navigationController.navigationBar;
// bg.png为自己ps出来的想要的背景颜色。
[navigationBar setBackgroundImage:[UIImage imageNamed:@"bg.png"]
forBarPosition:UIBarPositionAny
barMetrics:UIBarMetricsDefault];
[navigationBar setShadowImage:[UIImage new]];
这是唯一一个隐藏这条线的官方用法，但是有一个缺陷-删除了translucency(半透明)