System object datatypes – PB Docs 2022

Objects as datatypes

System object datatypes are specific to PowerScript. You view a list
of all the system objects by selecting the System tab in the
Browser.

In building PowerBuilder applications, you manipulate objects such
as windows, menus, CommandButtons, ListBoxes, and graphs. Internally,
PowerBuilder defines each of these kinds of objects as a datatype. Usually
you do not need to concern yourself with these objects as datatypes — you
simply define the objects in a PowerBuilder painter and use them.

However, sometimes you need to understand how PowerBuilder maintains
its system objects in a hierarchy of datatypes. For example, when you need
to define instances of a window, you define variables whose datatype is
window. When you need to create an instance of a menu to pop up in a
window, you define a variable whose datatype is menu.

PowerBuilder maintains its system objects in a class hierarchy. Each
type of object is a class. The classes form an inheritance hierarchy of
ancestors and descendants.

Examples

All the classes shown in the Browser are actually datatypes that you
can use in your applications. You can define variables whose type is any
class.

For example, the following code defines window and menu
variables:

If you have a series of buttons in a window and need to keep track
of one of them (such as the last one clicked), you can declare a variable
of type CommandButton and assign it the appropriate button in the
window:

Because it is a CommandButton, the LastClicked variable has all the
properties of a CommandButton. After the last assignment above,
LastClicked’s properties have the same values as the most recently clicked
button in the window.

To learn more about working with instances of objects through
datatypes, see About
objects.