UIScrollView 與 Auto Layout
讓 UIScrollVIew 自己管理 content size
- 用一個 UIView 當做 container (contnetView)
- container 與 self.view equal width
- UIView
- UIScrollView
- UIView (contentView) <--- 與 self.view equal width
- UIView (topContainer)
- UIView (bodyContainer)
- UIView (footerContainer)
...etc