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.
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:
window mywin
menu mymenu
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:
// Instance variable in a window
commandbutton LastClicked
// In Clicked event for a button in the window.
// Indicates that the button was the last one
// clicked by the user.
LastClicked = This
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”.
