BUG: Custom OCX Not Unloaded When Client Application Ends (173351)


The information in this article applies to:

  • Microsoft Visual Basic Learning Edition for Windows 5.0
  • Microsoft Visual Basic Learning Edition for Windows 6.0
  • Microsoft Visual Basic Professional Edition for Windows 5.0
  • Microsoft Visual Basic Professional Edition for Windows 6.0
  • Microsoft Visual Basic Enterprise Edition for Windows 5.0
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0
This article was previously published under Q173351

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.
Modification Type:MajorLast Reviewed:5/13/2003
Keywords:kbbug KB173351
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