PRB: OLE Servers Don't Unload When Last Object Set to Nothing

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

An OLE Automation server created with Visual Basic fails to unload from memory when the last instance of the object is destroyed.

CAUSE

A Visual Basic client can destroy the last instance of a Visual Basic OLE server it created by:

• Setting it to Nothing (the preferred method).
• Shutting down by unloading the last form (acceptable, but not as good).
• Ending the program by using the End statement (this is not recommended; it can cause problems because the QueryUnload, Unload, and Terminate events don't fire)

RESOLUTION

OLE servers are responsible for cleaning up any objects that they create or load. When an OLE server is unloaded, the Terminate event will be fired. This is where code should be located to unload any forms that the OLE server has in memory.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior in Visual Basic 4.0

1. Begin with a minimal OLE server and client application. For information on how to do this, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q129801

      TITLE     : How to Create and Use a Minimal OLE Automation Server
   
   

2. Add a form (Form1) to the OLE server.

3. Add a timer control (Timer1) to Form1.

4. Set the following properties:

      Object   Property    Value
      --------------------------
      Form1    Visible     False
      Timer1   Enabled     True
      Timer1   Internal    2000
   
   

5. Add the following code to the Timer1_Timer event procedure:

      Private Sub Timer1_Timer ()
         Beep
      End Sub
   
   

6. Add the following code to the General Declarations section of Class1:

   Dim frmX As New Form1

7. Add the following line to the existing MyClass_Initialize event procedure:

   Load frmX

8. Start the OLE server program by pressing the F5 key.

9. Minimize Visual Basic.

10. Start a second instance of Visual Basic.

11. Open (or create) the OLE client application described in Phase 2 of

        the article referenced in step 1.
    

12. Start the OLE client program running by pressing the F5 key.

13. Click Form1 of the OLE client program. The OLE server is created and

        begins beeping every two seconds.
    

14. Close the OLE client application. Notice that the OLE server continues

        to beep.
    

With the above OLE server add the following code to the MyClass_Terminate event:

   Private Sub MyClass_Terminate ()
      Unload frmX
   End Sub