Q248985: BUG: UserControl Containing ADO Data Control Fails to Unload

Article: Q248985
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbActiveX kbCtrl kbVBp kbVBp600bug kbGrpDSVB kbDSupport
Last Modified: 30-JAN-2000

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The information in this article applies to:

- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
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SYMPTOMS
========

When a contained (inside a UserControl) control's DataSource property is set to
a contained ActiveX Data Objects (ADO) Data Control (MSADODC.OCX) at run-time,
the container UserControl may fail to unload even when the form hosting the
control is unloaded. As a result, the Terminate event of the UserControl does
not fire as expected and if the form hosting the control is repeatedly loaded
and unloaded, a memory leak may occur.

RESOLUTION
==========

To work around the problem, use a temporary recordset as described in the "More
Information" section.

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 (Project1.) Form1 is created by default.

2. From the Project menu, add another form named Form2, and a UserControl named
  UserControl1.

3. From the Project menu, choose Components, and select Microsoft ADO Data
  Control 6.0 (OLEDB). Click OK.

4. From the Project menu, choose References, and then select Microsoft ActiveX
  Data Objects Recordset 1.5 Library. Click OK.

5. Add a text box named Text1, a command button named Command1, an ADO Data
  Control (Adodc1), and the following code to UserControl1:

  Private Sub Command1_Click()
     Set Text1.DataSource = Adodc1
     ' do something
     Set Text1.DataSource = Nothing
  End Sub

  Private Sub UserControl_Terminate()
     MsgBox "UserControl_Terminate"
  End Sub

6. Add an instance of the UserControl, a command button named Command1, and the
  following code to Form2:

  Private Sub Command1_Click()
     Unload Me
  End Sub

  Private Sub Form_Terminate()
     MsgBox "Form2 Terminate"
  End Sub

7. Add a command button named Command1 and the following code to Form1:

  Private Sub Command1_Click()
     Form2.Show vbModal
  End Sub

8. Press F5 to run the project and then click Command1 on Form1. You will then
  see Form2 display.

9. Press Command1 on the UserControl that is hosted in Form2, and then close
  Form2. You will see the Terminate event for Form2 fire, but the
  UserControl1's Terminate event does not fire (it will fire when you close the
  application).

10. To work around the problem, replace the code of Command1_Click() in the
  UserControl with this code:

  Private Sub Command1_Click()
     Dim rs As RecordSet
     Set rs = Adodc1.RecordSet
     Set Text1.DataSource = rs

     ' do something
     Set Text1.DataSource = Nothing
     Set rs = Nothing
  End Sub

  Repeat the previous test and note that the UserControl terminates normally.

Additional query words:

======================================================================
Keywords          : kbActiveX kbCtrl kbVBp kbVBp600bug kbGrpDSVB kbDSupport 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVB600
Version           : WINDOWS:6.0
Issue type        : kbbug
Solution Type     : kbnofix

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