Objects Parameters Are Passed by Reference

 Last reviewed: April 30, 1996
Article ID: Q130834
The information in this article applies to:
  • Microsoft Visual FoxPro for Windows, version 3.0

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 reference words: 3.00 VFoxWin
KBCategory: kbprg kbcode
KBSubcategory: FxprgClassoop

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last reviewed: April 30, 1996
© 1998 Microsoft Corporation. All rights reserved. Terms of Use.