How to always makes a UIScrollView scrollable?

In swift:

scrollView.alwaysBounceVertical = true
scrollView.alwaysBounceHorizontal = true

There are two properties on UIScrollView that sound like what you want:

@property(nonatomic) BOOL alwaysBounceVertical; // default NO. if YES and bounces is YES, even if content is smaller than bounds, allow drag vertically
@property(nonatomic) BOOL alwaysBounceHorizontal; // default NO. if YES and bounces is YES, even if content is smaller than bounds, allow drag horizontally

Simply set one or both of them to YES and you will get the bounce effect.

This can also be set in IB by checking the "Bounce Horizontally" and/or "Bounce Vertically" box(s):