Chapter 8: How Do I Handle Input from the User?
Apps need users, and designing an app’s UI is a major part of the app development process. iOS stands between the design and your app, sending messages to your app when the user interacts with the screen and sending messages to the screen when your app responds. To make a UI live, you must link your code to the objects that appear on the screen. You can use Interface Builder to create and edit links. IB includes some useful automation that simplifies the process for you. But before you can use it, you must learn how messages pass in both directions and discover what linking means in practice.