Chapter 12 CHAPTER 12 Model-View-Controller Pattern 12 According to the standard model billions of years ago some little quantum fluctuation, perhaps a slightly lower density of matter, maybe right where we're sitting right now, caused our galaxy to start collapsing around here. --Seth Lloyd We view things not only from different sides, but with different eyes; we have no wish to find them alike. --Blaise Pascal The primary symptom of a controller is denial, that is I can't see its symptoms in myself. --Keith Miller What Is the Model-View-Controller (MVC) Pattern? The Model-View-Controller (MVC) is a compound pattern, or multiple patterns working together to create complex applications. The MVC pattern is most com- monly used to create interfaces for software applications, and, as the name implies, consists of three elements. Model Contains the application data and logic to manage the state of the application View Presents the user interface and the state of the application onscreen Controller Handles user input to change the state of the application The power of the MVC pattern can be directly attributed to the separation of the three elements without overlap in each of their responsibilities. Let's look at each ele- ment's responsibilities. 427