Workplace Shell Object Types

There are three main classes in the WPS class hierarchy, descended from WPObject. The WPS classes are shown in Figure "Workplace Shell Class Hierarchy"

Classes are used to create the instances, or objects, that the user sees on the desktop. Each can be subclassed to create a new, derived class which inherits some of the properties and behaviors of the parent. Two useful terms to note here are base class, a class which is a direct subclass of WPObject, and persistence, which denotes that an object knows how to save its current state.

The main WPS classes are:

WPObject

The superclass from which all base classes are derived.

A base class that provides persistence via the OS2.INI file. These include programs, shadow copies and system objects such as the clock. They can be copied around the Workplace Shell but not to diskette.

A base class that provides persistence via the .CLASSINFO extended attribute of the associated file or directory. Objects of this class are always stored on disk. They are typically folders and files and can be copied to any media.

A base class that has no persistence. Examples of WPTransient objects are the window list and the printer drivers.