Extended widgets

Common Widgets provides a framework for developing custom widgets based on existing widgets. These are called extended widgets. If the VA Smalltalk portable API is used to develop an extended widget, it will be portable between all platforms supported by VA Smalltalk. Extended widgets are often implemented using a CwDrawingArea, with its visual appearance drawn using Common Graphics calls, and with user input processed using event handlers.

Consider the following subset of the CwWidget class hierarchy:

CwWidget

CwBasicWidget

CwComposite

CwPrimitive

CwShell

CwExtendedWidget

CwExtendedComposite

CwExtendedPrimitive

The CwWidget class defines behavior common to all widgets. The CwBasicWidget hierarchy provides the basic widgets described thus far, such as CwShell, CwText, CwList, CwPushButton, CwForm and CwRowColumn. Basic widgets are implemented using the native widgets provided by each platform. The implementation of basic widgets is not portable.

The CwExtendedWidget class is the abstract superclass of all extended widgets. As with the basic widget class hierarchy, it is divided up into primitive widgets (CwExtendedPrimitive) and composite widgets (CwExtendedComposite).