ios - iphone scrollview and imageview autoresize

Question

I am using xcode 4.3.2.

I have an imageView inside a scrollView, with the contentMode for both set as aspect fill.

My problem is after I rotate the orientation, the screen focuses on the center of the image.

When I scroll down there is a blank part under the image. When I try to scroll up, it bounce me back, so actually I cannot stay at the top of scrollView

我将contentsize滚动视图的大小设置为手机上显示的实际图像的大小（不是原始图像大小），

两个框架的原点都是 0, 0 所以当我旋转手机时任何人都可以帮助解决这个问题。