Q143048: BUG: Form Unload in Any DBGrid Event Ends Visual Basic

Article: Q143048
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0
Operating System(s): 
Keyword(s): kbnokeyword kbVBp400 kbGrpDSVBDBkbbuglist
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
========

Unloading a form with a DBGrid control by using the Unload statement in the any
event of the DBGrid control causes an application error that ends the Visual
Basic program. The following are ways to work around this issue:

- Set the form to nothing prior to unloading the form.

  -or-

- Unload the form in an event other than a DBGrid event.


STATUS
======

Microsoft has confirmed this to be an issue in the Microsoft products listed at
the beginning of this article. Microsoft is researching this problem and will
post new information here in the Microsoft Knowledge Base as it becomes
available.

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

The following is an example to reproduce this behavior. Two forms are used:

- The first form has a command button that shows the second form.

- The second form contains the DBGrid control. The click event of the DBGrid
  control unloads the second form. Run the program and click the command button
  to show the second form. Click the DBGrid control in the second form and the
  application error occurs.

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

1. Start Visual Basic 4.0 or if it is already running, click New Project on the
  File menu.

2. Add a command button to the Form1 form.

3. Copy the following code sample to the Form1 code window:

        Option Explicit

        Private Sub Command1_Click()
           'Show Form2
           Form2.Show
        End Sub

4. On the Insert menu, click Form to insert a second form into the project.

5. Add a DBGrid control to the Form2 form and copy the following code sample to
  the Form2 code window:

        Option Explicit

        Private Sub DBGrid1_Click()
           'Remove the comment marks from the next two lines
           'to work around the bug.
           'Form2.Hide
           'Set Form2 = Nothing
           Unload Form2
        End Sub

6. On the Run menu, click Start, or press the F5 key to start the program. Click
  the Command1 command button to display the second form. Click on the DBGrid
  control in the second form. An application error occurs with the following
  message and Visual Basic ends:


  32-bit Visual Basic 4.0:

     Windows NT-An application error has occurred and an application
                     error log is being generated. VB32.exe, Exception:
                     access violation (0xc0000005), Address: 0x022a00b8.

     Windows 95-VB32 caused and invalid page fault in module <unknown> at
                0000:00000015.

  16-bit edition of Visual Basic 4.0:

     All Operating Systems - VB caused a general protection fault in
                             module DBGrid16.OCX at 0003:0000fb7f.

Additional query words: 4.00 vb4win vb4all

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Keywords          : kbnokeyword kbVBp400 kbGrpDSVBDB kbbuglist
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch
Version           : WINDOWS:4.0
Issue type        : kbbug

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