All visible objects in an application are either windows or views. In this chapter, you will create a subclass of
NSView. From time to time, you may need to create a custom view to do custom drawing or event handling. Even if you do not plan to do custom drawing or event handling, by learning how to create a new view class, you will learn a lot about how Cocoa works.
Windows are instances of the class
NSWindow. Each window has a collection of views, each of which is responsible for a rectangle of the window. The view draws inside that rectangle and handles mouse events that occur there. A view may also handle keyboard events. You have worked with several subclasses of