iPad Application Development For Dummies, 3rd Edition

View Controllers — the Main Storyboard Players

Early in this chapter, I provide an overview of the storyboard — the white board, so to speak, on which you lay out the flow of the elements, or design pattern, of your application. In this book, the example application developed throughout — RoadTrip — uses the Model-View-Controller (MVC) design pattern, and in this particular design pattern, it’s the view controllers that implement the pattern’s controller component. These controller objects contain the code that connects the app’s view objects to its model objects. Whenever the view needs to display something, the view controller goes out and gets what the view needs from the model. Similarly, view controllers respond to controls in your Content view and may do things like tell the model to update its data (when the user adds or changes text in a text field, for example), compute something (the current value of, say, your U.S. dollars in British pounds), or change the view being displayed (like when the user presses the Detail Disclosure button on the iPod application to find out more about a song).

View controllers, as you can see in Figure 4-12, are the objects that control what is displayed and that respond to user actions. They are the heart and soul of the storyboard.

As I explain in more detail in Chapter 9, a view controller is often the (target) object that responds to the onscreen controls. The Target-Action mechanism is what enables the view controller to be aware of any ...