The Core iOS Developer’s Cookbook, Fifth Edition

Touches and Responder Methods

All subclasses of the UIResponder class, including UIView and UIViewController, respond to touches. Each class decides whether and how to respond. When choosing to do so, they implement customized behavior when a user touches one or more fingers down in a view or window.

Predefined callback methods handle the start, movement, and release of touches from the screen. Corresponding to the phases you’ve already seen, the methods involved are as follows:

touchesBegan:withEvent:—Gets called at the starting phase of the event, as the user starts touching the screen.

touchesMoved:withEvent:—Handles the movement of the fingers ...