Windows and messages are the bones and blood of the Windows CE operating system. A message is the means by which the user communicates with Windows CE and your application. A window object, which is usually referred to as a window, is the means by which an application receives messages from the user and the operating system.
In Windows CE-based systems with graphical displays, windows are the primary input and output devices. Applications use the graphics device interface (GDI) to display output in a window. The messaging system passes user input to a window in the form of messages. Unlike Windows-based desktop platforms, not all Windows CE-based devices have a graphical display. However, because all applications need to process messages, all applications must have windows, even those that do not have a graphical display.
Every window is a member of a window class. A window class is a template for creating window objects. When you write an application, you register at least one window class that you use to create a window or windows.
Note Windows CE does not support dynamic data exchange (DDE), multiple-document interface (MDI), or window properties.
For specific information about designing windows, see Designing the User Interface for Windows CE.