ios scrollview放大之偏移的问题

场景:

1. scrollView.frame = viewController.bounds
2. 要放大的view的宽度小于scrollView的宽度

问题：
当放大之后出现了偏移

Paste_Image.png

加上如下代码 问题解决

func scrollViewDidZoom(scrollView: UIScrollView) {
        let  offsetX:CGFloat = (scrollView.bounds.size.width  >  scrollView.contentSize.width) ? (scrollView.bounds.size.width - scrollView.contentSize.width) * 0.5 : 0.0;
        let  offsetY:CGFloat = (scrollView.bounds.size.height > scrollView.contentSize.height) ? (scrollView.bounds.size.height - scrollView.contentSize.height) * 0.5 : 0.0;
        self.drawView!.center = CGPointMake(scrollView.contentSize.width * 0.5 + offsetX,
        scrollView.contentSize.height * 0.5 + offsetY);

    }