DOCUMENT:Q192682  17-SEP-1998  [vbwin]
TITLE   :BUG: Dynamically-Added OCX Event Parameter Is Not Passed ByRef
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:WINDOWS:6.0
OPER/SYS:WINDOWS
KEYWORDS:

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

 - Microsoft Visual Basic Learning, Professional, and Enterprise Editions
   for Windows, version 6.0
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SYMPTOMS
========

When working with an ActiveX control that is added dynamically at run-time,
an event procedure passes a Variant parameter by reference (ByRef) to the
client, but any changes made by the client are not returned to the control.

CAUSE
=====

This occurs when the event procedure is written to pass a Variant, but the
variable being passed by the control is not a Variant. This causes Visual
Basic to create a temporary Variant to use as the event parameter. When the
client code makes changes to the parameter, the changes are made to this
temporary copy and not to the original variable.

Under normal circumstances, Visual Basic updates the original variable with
any changes made to the Variant copy. However, this does not occur for
event procedures in a dynamically-loaded UserControl.

RESOLUTION
==========

To avoid the problem, make sure the data types of your UserControl event
procedures are as specific as possible. Also, see that the parameters used
during a RaiseEvent call match the expected parameter types.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed
at the beginning of this article.

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

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

1. Create a Standard EXE project. Form1 is created by default.

2. Add a UserControl project to the group. This should be Project2.

3. Add a CommandButton to the UserControl and place the following in the
   code window for UserControl1:

      Event Click(X As Variant)

      Private Sub Command1_Click()
         Dim MyValue As Long  ' Notice MyValue is declared as Long
         MyValue = 1
         MsgBox "Value before event is raised: " & MyValue
         RaiseEvent Click(MyValue)
         MsgBox "Value after then event returns: " & MyValue
      End Sub

4. Close the UserControl designer.

5. In the code window for Form1, add the following:

      Dim WithEvents DynCtl As VBControlExtender

      Private Sub Form_Load()
         Set DynCtl = Controls.Add("Project2.UserControl1", "Tester")
         DynCtl.Visible = True
      End Sub

      Private Sub DynCtl_ObjectEvent(Info As EventInfo)
         ' Change the ByRef value to 1000000
         Info.EventParameters.Item(0).Value = 1000000
         MsgBox "Value after change in ObjectEvent: " & _
            Info.EventParameters.Item(0).Value
      End Sub

6. Press the F5 key to run Project1 and click on the CommandButton. You
   should see a message box showing the value of the original variable
   before raising the "Click" event. This is followed by another message
   box showing the value of the parameter after it has been changed by the
   client. Finally, the last message box shows the value of the original
   variable after the event has been raised. Note that the changes made
   by the client are not reflected in the last message box.

7. To correct the problem, change the declaration of the MyValue variable
   (in Project2.UserControl1's CommandButton code) from a Long to a
   Variant. Re-run Project1. The code should now work correctly because
   Visual Basic no longer needs to create a temporary variable for the
   event parameter.

REFERENCES
==========

For additional information, please see the following article in the
Microsoft Knowledge Base:

   ARTICLE-ID: Q190670
   TITLE     : HOWTO: Dynamically Add Controls to a Form with Visual
               Basic 6.0

Additional query words: kbDSupport kbDSD kbVBp kbCtrl kbVBp600bug
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Version           : WINDOWS:6.0
Platform          : WINDOWS
Issue type        : kbbug

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

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