How do I enable directional lock for a UIScrollView?

You'll be subclassing UIScrollView and overriding the touchesBegan:withEvent: method, touchesMoved:withEvent: method, and the touchesEnded:withEvent: method.

You'll use those methods, along with the start and end points of a touch, to calculate what kind of touch event took place: was it a simple tap, or a horizontal or vertical swipe?

If it is a horizontal swipe, you cancel the touch event.

Take a look at the source code here to learn how you might get started.

First, set the UIScrollView's contentSize to have a width that is equal to or less than the width of the UIScrollView's frame.

Next, set UIScrollView's alwaysBounceHorizontal to NO. This will prevent the scroll view from "rubber banding" even though you've told it there's no more horizontal content to display.

UIScrollView *scrollView;
CGSize size = scrollView.contentSize;
size.width = CGRectGetWidth(scrollView.frame);
scrollView.contentSize = size;
scrollView.alwaysBounceHorizontal = NO;

It doesn't matter what's actually inside the scroll view.

Swift 5.0

let scrollView = UIScrollView() // Or however you want to initialize it
var size = scrollView.contentSize
size.width = scrollView.frame.width
scrollView.contentSize = size
scrollView.alwaysBounceHorizontal = false