DOCUMENT:Q130834  15-FEB-2000  [foxpro]
TITLE   :Objects Parameters Are Passed by Reference
PRODUCT :Microsoft FoxPro
PROD/VER:WINDOWS:3.0
OPER/SYS:
KEYWORDS:kbcode

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The information in this article applies to:

 - Microsoft Visual FoxPro for Windows, version 3.0 
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SUMMARY
=======

By default, parameters are passed by value to user-defined functions and by
reference to procedures called with a DO command. This article explains how an
Object-type variable is passed as a parameter.

MORE INFORMATION
================

Object variables are always passed by reference to user-defined functions and
procedures. Creating an object creates a reference to an object of a class. When
a procedure or a method receives an object as a parameter, any change made to
the parameter affects the object. Only one instance of the object actually
exists; the parameter points to the same object as the instance variable.

To pass an Object reference from a form, you can use this syntax:

      Thisform.mymethod(this)

   -or-

      Thisform.mymethod

In the following example code, a form is created, and the ChangeCaption method of
the form is called. Controls are passed as parameters. This example could have
been programmed differently by making the ChangeCaption a method of any control.
It is included to illustrate how object type variables are passed as
parameters.

Sample code
-----------

   PUBLIC oForm
   oForm=CREATEOBJECT('Myform')
   oForm.show
   =MESSAGEBOX('Note the Caption of the CommandButton')
   oForm.ChangeCaption(oform.mycmd)
   =MESSAGEBOX('Note the Caption of the CommandButton')

   DEFINE CLASS myform as FORM

     ADD OBJECT mycmd as COMMANDBUTTON with Caption = "Before"
     ADD OBJECT cmdquit1 as cmdquit

     PROCEDURE ChangeCaption
     PARAMETER objref
     objref.Caption="After"
     ENDPROC

   ENDDEFINE

   DEFINE CLASS cmdquit as COMMANDBUTTON
     Caption= "Quit"
     Top=25
     Left=25
     PROCEDURE Click
       RELEASE Thisform
     ENDPROC
   ENDDEFINE

Additional query words: VFoxWin

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Keywords          : kbcode 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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