iOS隐藏导航栏下面的黑线

- (void)viewWillAppear:(BOOL)animated{
    
    [super viewWillAppear:animated];
    //隐藏黑线
    [self useMethodToFindBlackLineAndHindWithHidden:YES];

}

- (void)viewWillDisappear:(BOOL)animated{
    
    [super viewWillDisappear:animated];
    //显示黑线
    [self useMethodToFindBlackLineAndHindWithHidden:NO];

}

- (void)useMethodToFindBlackLineAndHindWithHidden:(BOOL)hidden{
    
    UIImageView* blackLineImageView = [self findHairlineImageViewUnder:self.navigationController.navigationBar];
    //隐藏黑线（在viewWillAppear时隐藏，在viewWillDisappear时显示）
    blackLineImageView.hidden = hidden;
    
}

- (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;
}