您需要设置UIScrollView的大小，使其小于contentsize。否则它不会滚动。

You need to set the size of your UIScrollView so that it is less then the contentsize. Otherwise it won't scroll.

我还建议添加 scroller.contentSize = CGSizeMake（400,2300）到您的 viewDidLoad 方法。

Also I would recommend to add scroller.contentSize = CGSizeMake(400, 2300) to your viewDidLoad method.