下拉放大图片

设置scrollView(包括其子类)偏移量

 tableView.contentInset = UIEdgeInsetsMake(200, 0, 0, 0)

设置图片frame值，和图片显示模式

ImageView.frame = CGRectMake(0, -200, tableView.frame.width, 200)ImageView.contentMode = .ScaleAspectFill

监听scrollView滚动，修改图片frame值

override func scrollViewDidScroll(scrollView: UIScrollView) {        let yOffset = scrollView.contentOffset.y        if yOffset < CGFloat(-200) {            var imageViewframe = ImageView.frame            imageViewframe.origin.y = yOffset            imageViewframe.size.height = -yOffset            ImageView.frame = imageViewframe        }    }