iPhone Open Application Development

Windows and Views

The most basic user interface component is a window. A window is a region of screen space: a picture frame. UIWindow is the iPhone's base window class and is derived from lower level functions that respond to mouse events, gestures, and other types of events that would be relevant to a window. The UIWindow class is ultimately responsible for holding the contents of a UIView object (the picture that fits in the window's frame). UIView is a base class from which many other types of display classes are derived. The window itself can only hold one object, whereas the UIView object is designed to accommodate many different types of subobjects, including other views. The two classes go hand-in-hand with each other, and both are required to display anything on the iPhone screen.

Creating a Window and View

Before you can display anything on the iPhone screen, you must create a window to hold content, and to build a window, you need a display region. A display region is a fancy term for rectangle and represents the portion of the screen where the window should be displayed. The underlying structure itself is a rectangle structure named CGRect that contains two pieces: the coordinates for the upper-left corner of the window and the window's size (its width and height). Every object displayed on the screen has a display region defining its display area. Most are set when the object is initialized, via an initWithFrame method. Others must be set after the fact using a ubiquitous ...