How to Use the GETPEM() Function (143205)

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Syntax

The syntax of GETPEM() is as follows:

   GETPEM(oObjectName | cClassName, cProperty | cEvent | cMethod)
				

GETPEM receives either an object name or a class name as a first parameter. This means that the GETPEM() function does not require an instance of the class to return a value. In the following example, GETPEM is called to return the value of a property. The first time GETPEM is used, the first parameter is an object name. The second GETPEM verifies the value of the Caption property at the class level.

   oObjRef=CreateObject('myform')
   oObjRef.Show
   oObjRef.Caption="Testing the New Function"
   ?'Caption of the Object: '
   ??GETPEM(oObjref,'Caption')
   ?'Caption in the Class: '
   ??GETPEM('myform','Caption')
   =Messagebox('Press Any Key to Clear')

   DEFINE CLASS myform as Form
     Caption="Testing GETPEM"
   ENDDEFINE
				

Note that the first parameter does not require quotation marks when it is a variable that references an object. However, if the first parameter is the name of a class, and you do not type quotation marks, the error "Variable <var> is not Found" is returned.

Using GETPEM with Visual FoxPro Base Classes or User Defined Classes

GETPEM can return the value of a property of a base class. For example, to determine the default font of a text box, you can use the following command:

   ?GETPEM('TextBox','FontName')
				

You can use this to determine default attributes of objects before you modify them. To return a value on a user defined class, GETPEM requires that the class be cached in memory. It does not, however, require that an instance of the class actually exist. To have a class cached in memory, you need to create an instance of the user defined class. You can then release this instance. For example:

   oTool1=CREATEOBJECT('ToolBar')
   oTool1=.NULL.
				

A CLEAR ALL or CLEAR CLASS ClassName would release the class from memory. Note that GETPEM does not search a Visual Class Library (VCX) opened with the SET CLASSLIB command. You also need to create an instance of the class and release it when you search a class defined in a VCX.

Calling GETPEM at design time

The GETPEM() function can be called at design time or at run time. The following step-by-step example shows how you can use GETPEM with SYS(1270) to return the value of a property. By using SYS(1270), you don't need to make an explicit call to a variable reference.

1. In the Command window, type

   ON KEY LABEL F7 WAIT WINDOW GETPEM(SYS(1270),'Class')

2. Create a form, and place a command button and text box on the form.
3. Position the mouse pointer over one control, and press the F7 key. A window displays the class name of the control.

Using GETPEM to Return Event Code

The GETPEM function is also useful to return method or event code. Although you cannot write method code at run time, you can use GETPEM to help you debug an application. The following example prints the code of a method that generates an error.

1. Create a form.
2. Add a command button to a form.
3. In the Click event of the button, add this code:

      RELAESE THISFORM   && error that calls the event handler
   						

4. In the Error event handler of the button, type:

      LPARAMETERS nError, cMethod, nLine
      ACTIVATE SCREEN
      ?'ERROR'+ALLTRIM(STR(nError))+'IN LINE'+ALLTRIM(STR(nLine))+':'
      ?GETPEM(THIS,cMethod)
   						

5. Save and run the form. When the form is displayed, click the command button. It contains an error that calls the Error event. The method code is then printed to the screen.