Q174004: FIX: Cannot Change Variant Array in Class Module

Article: Q174004
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0,5.0
Operating System(s): 
Keyword(s): kbVBp400 kbVBp500 kbGrpDSVB
Last Modified: 11-JAN-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, version 5.0 
- Microsoft Visual Basic Professional Edition for Windows, version 5.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 5.0 
- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

In Visual Basic 4.0, an array stored in a variant class variable could be
changed from code external to the class. In Visual Basic 5.0, changing values in
the array will have no effect.

CAUSE
=====

The behavior of Visual Basic 4.0 was incorrect. This has been corrected in
Visual Basic 5.0. In Visual Basic 4.0, storing an array in a variant variable
was commonly used as a workaround for the fact that arrays cannot be declared as
Public members of a class. However, this workaround is neither necessary nor
recommended. If the approach outlined in the next section had been used, this
problem would not have occurred regardless of the version of Visual Basic in
use.

RESOLUTION
==========

Arrays cannot be declared as Public members of a class. The recommended method
of implementing an array as a member of a class is to declare the array as
Private, and create Property Let and Get methods to manage the array. For
example:

     Private myarray() as String

     Public Property Get marray(ByVal subscript As Integer) As String
     marray = myarray(subscript)
     End Property

     Public Property Let marray(ByVal subscript As Integer, _
        ByVal vNewValue As String)
     On Error GoTo err_Array_Not_Initialized
     If subscript > UBound(myarray) Then
        ReDim Preserve myarray(subscript)
     End If
     myarray(subscript) = vNewValue
     Exit Property

     err_Array_Not_Initialized:
     If Err.Number = 9 Then
        ReDim myarray(1)
        Resume
     End If
     End Property

STATUS
======

This problem has been corrected in Visual Basic 5.0.

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

Microsoft has acknowledged that this change in behavior may be an issue for some
developers porting Visual Basic 4.0 code to Visual Basic 5.0. Code that relies
on the functionality shown below, and acceptable in Visual Basic 4.0, will need
to be modified.

Steps to Reproduce Behavior That Was Previously Acceptable
----------------------------------------------------------

1. Create a new "Standard EXE" project in Visual Basic 5.0.

2. Add a Class Module to the project.

3. Add the following code to Class1:

        Public aVariant As Variant

        Private Sub Class_Initialize()
        Dim anArray(2)
           anArray(1) = "Hello"
           anArray(2) = "World"
           aVariant = anArray
        End Sub

4. Add the following code to the Click event of Form1:

        Private Sub Form_Click()
        Dim obj As New Class1
           With obj
              .aVariant(1) = "Goodbye"
              .aVariant(2) = "Everyone"
              Debug.Print .aVariant(1)
              Debug.Print .aVariant(2)
           End With
           Set obj = Nothing
        End Sub

5. Run the project and click on Form1. Note that the values displayed in the
  immediate window are "Hello" and "World", which are the original values
  assigned to the array during the class initialization event.

6. If desired, repeat steps 1 through 5 in Visual Basic 4.0. Note that the
  values displayed in the immediate window are "Goodbye" and "Everyone."

Additional query words:

======================================================================
Keywords          : kbVBp400 kbVBp500 kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVBA500 kbVB500 kbVB400Search kbVB400 kbVB16bitSearch
Version           : WINDOWS:4.0,5.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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.

Copyright Microsoft Corporation 1986-2002.