BUG: UserControl Containing ADO Data Control Fails to Unload

• Microsoft Visual Basic Enterprise Edition for Windows, version 6.0

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 kbGrpVB kbDSupport
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbbug