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Q142839: Unloading Form from Within DBGrid Event Causes GPF

Article: Q142839
Product(s): Microsoft Visual Basic for Windows
Version(s): 4.00 | 4.00
Operating System(s): 
Keyword(s): kbDatabase
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
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SYMPTOMS
========

When unloading a form from within an event of a Data Bound Grid control a
General Protection fault will occur in VB.EXE or an Exception fault will occur
in VB32.EXE.

CAUSE
=====

The cause of the problem is that the unload event is destroying the recordset
object of the data control. When the DBGrid gets control back the recordset
pointer is no longer valid.

STATUS
======

Microsoft has confirmed this to be a problem in Visual Basic version 4.0. We are
researching this problem and will post new information here in the Microsoft
Knowledge Base as it becomes available.

WORKAROUND
==========

To work around this problem, add a timer control to the form and allow the
"Unload Me" command to happen here rather than in the DBGrid control. Here is a
step-by-step example to correct the problem:

1. Add a timer control to the form. Set its Enabled property to False and its
  Interval property to 5.

2. In the timer event of the timer control add 2 lines of code:

     Timer1.Enabled = False
     Unload Me

3. In the event of the DBGrid that you wish to unload the form add this line of
  code:

     Timer1.Enabled = True

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

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

1. Start Visual Basic, or if it is already running, select New Project from the
  File menu.

2. Add a data control to Form1.

3. Set these properties of Data1:

  DatabaseName: BIBLIO.MDB
  RecordSource: Authors

4. Add a DBGrid control to the form.

5. Set this single property of DBGrid1:

  DataSource: Data1

6. Add this line of code to the Click event of the DBGrid control:

     Private Sub DBGrid1_Click()
               Unload Me
     End Sub

7. Press F5 to run the project. Click the DBGrid. You will now get an Unhandled
  exception in VB32.EXE or a General Protection Fault in module DBGRID16.OCX at
  0002:FB7F.

Additional query words: 4.00 vb4win vb4all gp-f gpf gp

======================================================================
Keywords          : kbDatabase 
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch
Version           : 4.00 | 4.00

=============================================================================

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