當(dāng)導(dǎo)航欄多出了黑線是imageView導(dǎo)致的.通過下面的這兩個方法可以去掉導(dǎo)航欄上面的細(xì)線.

//隱藏黑線
-(void)useMethodToFindBlackLineAndHind:(BOOL)isHidden
{
    UIImageView* blackLineImageView = [self findHairlineImageViewUnder:self.navigationController.navigationBar];
    //隱藏黑線（在viewWillAppear時隱藏，在viewWillDisappear時顯示）
    blackLineImageView.hidden = isHidden;
}

- (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;
}