Q190491: PRB: Access/Assign Not Called by DIMENSION, ADEL or AINS

Article: Q190491
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): 
Last Modified: 11-DEC-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
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SYMPTOMS
========

When you create an array that is a property of an object, you can also add
Access or Assign methods to the array property. If you DIMENSION the array, or
add or remove elements, rows, or columns with the AINS() or ADEL() functions,
the Access and Assign methods are not called.

STATUS
======

This behavior is by design.

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

The Access and Assign methods are new in Visual FoxPro 6.0. In effect, they
allow you to attach events to properties. When the property's value(s) are
queried (Access method), or when the property's values are set (Assign method),
you can execute user code. Because of the nature of arrays and their
manipulation, the Access and Assign methods associated with the array properties
behave differently than with non-array properties.

Steps to Reproduce Behavior
---------------------------

The following program instantiates a form from a form class definition. The form
contains an array property. The array is populated in the form's Load method. A
row is deleted from the array, the array is redimensioned, and a row is added
back into the array.

1. Run the following code from a program (.prg) file:

        Clear
        DEBUG
        _SCREEN.Show()
        DEBUGOUT " "
        DEBUGOUT " "
        oform1=NEWOBJECT("form1")
        DEBUGOUT " "
        oform1.PrintToScreen      && Output contents of array to screen
        =adel(oform1.atest,2)     && Deletes 2nd row
        DIME oform1.atest[alen(oform1.atest,1)-1,alen(oform1.atest,2)]
        DEBUGOUT " "
        oform1.PrintToScreen
        DIME oform1.atest[alen(oform1.atest,1)+1,alen(oform1.atest,2)]
        =ains(oform1.atest,2)     && insert before 2nd row
        DEBUGOUT " "
        oform1.PrintToScreen

        DEFINE CLASS form1 AS form

           Caption = "Form1"
           Name = "Form1"
           DIMENSION atest[3,2]

           PROCEDURE atest_access
              LPARAMETERS m.nIndex1,m.nIndex2
              * Echo current program and calling program to
              * Debug Output window
              DEBUGOUT "In " + PROGRAM()+", called from " ;
                 + PROGRAM(PROGRAM(-1)-1)
              RETURN THIS.atest[m.nIndex1,m.nIndex2]
           ENDPROC

           PROCEDURE atest_assign
              LPARAMETERS vNewVal,m.nIndex1,m.nIndex2
              * Echo current PROGRAM and calling PROGRAM to
              * Debug Output window
              DEBUGOUT "In "+PROGRAM()+", called from " ;
                 + PROGRAM(PROGRAM(-1)-1)
              this.atest[m.nIndex1,m.nIndex2] = m.vNewVal
           ENDPROC

        PROC PrintToScreen
           ?'    Column 1   Column 2'
           * Iterate through array and print each element
           FOR lnRow = 1 to alen(this.atest, 1)
              ?
              FOR lnCol = 1 to alen(this.atest, 2)
                 ??this.atest[lnRow, lnCol]
              ENDFOR
           ENDFOR
           ?
        PROCEDURE Load
           * Populate the array
           FOR lnRow = 1 to alen(this.atest, 1)
              FOR lnCol = 1 to alen(this.atest, 2)
                 this.atest[lnRow, lnCol] = 100 * lnRow + lnCol
              ENDFOR
           ENDFOR

          ENDPROC
        ENDDEFINE
   

2. The contents of the array is printed to the Visual FoxPro desktop three times
  by the PrintToScreen method. The first printing is the original contents. The
  second printing contains the contents after the second row is deleted and the
  third row is removed by the DIMENSION command. The third printing is the
  contents after a third row is added with DIMENSION and a new second row is
  inserted.

3. The DEBUGOUT command is used to output information to the Debug Output
  Window. The current program echos (either the Access or Assign method) and
  the calling program, one program back in the call stack, is returned by
  PROGRAM(PROGRAM(-1)-1)). Here you see that the atest_assign was called six
  times from the form Load method. The Atest_access was called six times, then
  four times, then six times as the three calls to PrintToScreen are executed.

REFERENCES
==========

Visual FoxPro Help file; search on: "Access and Assign methods" (without the
quotation marks); "DIMENSION" (without the quotation marks); "AINS()" (without
the quotation marks); "ADEL()" (without the quotation marks)
(c) Microsoft Corporation 1998, All Rights Reserved.
Contributions by Jim Saunders, Microsoft Corporation


Additional query words: kbVFp600 kbOOP

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbprb

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