iOS Programming: The Big Nerd Ranch Guide

For the More Curious: The Responder Chain

In Chapter 7, we talked briefly about UIResponder and the first responder. A UIResponder can receive touch events. UIView is one example of a UIResponder subclass, but there are many others, including UIViewController, UIApplication, and UIWindow. You are probably thinking, “But you can’t touch a UIViewController. It’s not an on-screen object.” You are right – you cannot send a touch event directly to a UIViewController, but view controllers can receive events through the responder chain.

Every UIResponder has a pointer called nextResponder, and together these objects make up the responder chain (Figure 12.5). A touch event starts at the view that was touched. The nextResponder of a view ...