Q173351: BUG: Custom OCX Not Unloaded When Client Application Ends

Article: Q173351
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SYMPTOMS
========

If a variable is set to reference a UserControl or one of its constituent
controls in the InitProperties and ReadProperties events of the UserControl, the
reference is not released when the client application ends; therefore, the OCX
remains loaded. Because the OCX does not unload, its Terminate event is not
triggered when the application ends.

RESOLUTION
==========

You can work around this problem by using a variable that saves the Name
property of the control rather than an actual reference to the control. For
example, if you are using the following code in a UserControl in which the
Terminate event is not triggered:

       Dim o As Object

       Private Sub UserControl_InitProperties()
         Set o = Label1
       End Sub

       Private Sub UserControl_ReadProperties(PropBag As PropertyBag)
         Set o = Label2
       End Sub

replace the code with the following:

       Dim s As String

       Private Sub UserControl_InitProperties()
         s = Label1.Name
       End Sub

       Private Sub UserControl_ReadProperties(PropBag As PropertyBag)
         s = Label2.Name
       End Sub

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. We are researching this bug and will post new
information here in the Microsoft Knowledge Base as it becomes available.

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

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

1. Start a new "ActiveX Control" project.

2. Add two Label controls to UserControl1.

3. Add the following code to UserControl1:

        Option Explicit

        Dim o As Object

        Private Sub UserControl_InitProperties()
           Set o = Label1
           MsgBox "InitProperties"
        End Sub

        Private Sub UserControl_ReadProperties(PropBag As PropertyBag)
            Set o = Label2
            MsgBox "ReadProperties"
        End Sub

        Private Sub UserControl_Terminate()
            MsgBox "Terminate"
        End Sub

4. Save the project and Make the OCX.

5. Start a new "Standard EXE" project.

6. Click Components on the Project menu. Check the custom OCX you built in step
  4.

7. Add the custom control to Form1. Note that the InitProperties event fires as
  expected.

8. Press the F5 key to run the program. Note that the ReadProperties event
  fires. However, you would expect to receive a Terminate event and then the
  ReadProperties event.

9. Click End on the Run menu. Note that only ReadProperties fires, not Terminate
  and then ReadProperties as expected.

10. Exit the IDE. Note that the OCX now unloads and the Terminate events are
  triggered.

Additional query words: kbVBp500bug kbVBp600bug kbVBp kbdsd kbDSupport KBCONTROL KBCTRLCREATE

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Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Issue type        : kbbug

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