The UIWindow class defines objects (known as windows ) that manage and coordinate the windows an application displays on the screen.
In iOS, windows and views are used to present application’s content on the screen. Windows do not have any visible content themselves but provide a basic container for application’s views. The two principal functions of a window are to provide an area for displaying its views and to distribute events to the views. The window is the root view in the view hierarchy. A window belongs to a level; the windows in one level appear above another level. For example, alerts appear above normal windows. Typically, there is only one window in an iOS application.
