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Article: Q150206
Product(s): Microsoft Visual Basic for Windows
Version(s): 4.00
Operating System(s): 
Keyword(s): kbbuglist
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, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
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SYMPTOMS
========

A program hangs if a DBGrid control is placed on a Modal Form, which itself was
invoked from a Modal form from an MDIChild window, and the form containing the
DBGrid is then closed. Usually the window receiving the focus after the form
with the DBGrid control is closed begins to flash, and does not respond to user
input.

STATUS
======

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

WORKAROUND
==========

Show the form containing the DBGrid in a non-modal fashion, and disable the
other forms in the project until the non-modal form is dismissed. The routine
below shows a form that appears as a modal form:

     Public Sub ShowModalForm(frmTarget As Form)

     Dim c As Collection
     Set c = New Collection

     'Disable all the forms
     For Each ofrm In Forms
         If ofrm.Enabled = True Then
         c.Add ofrm
         ofrm.Enabled = False
         End If

     Next ofrm

     'Now show the target form non-modal
     frmTarget.Show

     'If the frmTarget was disabled by the loop above
     '(because it was invisible) make sure it is now enabled

     frmTarget.Enabled = True

     'Sit in a loop until the target form is dismissed


     Do While frmTarget.Visible = True
     DoEvents
     Loop

     'FIX: Unload the Form
     UnLoad frmTarget

     'We have left the loop, so the dialog has been closed
     'Now Enable the forms that were disabled, and exit the procedure

     For Each ofrm In c
         ofrm.Enabled = True
     Next ofrm

     End Sub

Because a non-modal form cannot be shown from a modal form, the routine above
must also be used to show the form prior to the modal form containing the DBGrid
control.

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

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

1. Start a new project in the 32-bit edition of Microsoft Visual Basic. Form1 is
  created by default.

2. From the Insert menu, select MDI Form to insert an MDI Parent form.

3. From the Insert menu, select Form to insert two more regular forms into the
  project.

4. Choose Form1, and select the Properties window by pressing F4. Change the
  MDIChild property to True.

5. Place a Command button in Form1, and in the Click event place the following
  code:

     Private Sub Command1_Click()
        Form2.Show vbModal
     End Sub

6. Place a Command button on Form2, and in the Click event, place the following
  code:

     Private Sub Command1_Click()
        Form3.Show vbModal
     End Sub

7. On Form3, place a DBGrid control and a Data Control. Change the Databasename
  property of the Data control to "biblio.mdb" in the Visual Basic directory.
  Change the Recordsource property of the Data control to "Authors." Change the
  Datasource property of the DBGrid control to "Data1."

8. Run the project by pressing F5. Press the Command button on Form1 to show
  Form2 modally. Press the Command button on Form2 to show Form3 modally. Close
  Form3 using the Control box of the window. Note that Form2 flashes, and the
  program hangs.

To correct the problem in the Steps to Reproduce Problem section above, paste the
ShowModalForm routine contained above into a standard code module, and then
change the Command1_Click event in Form1 to:


     'FIX: Flag to avoid unloading the form when the user closes it
     Private mblnIgnoreUnload as boolean

     'FIX: Additional Code for Form_Load of Form2
     Private Sub Form_Load
         mblnIgnoreUnload = True
     End Sub

     'FIX: Additional Code for Form_QueryUnLoad of Form2
     Private Sub Form_QueryUnLoad
         If mblnIgnoreUnload Then
             Me.Hide ' Make Form2 Invisible
             Cancel = True ' Do not unload Form2
             mblnIgnoreUnload = False ' Next time we come here unload Form2
         End If
     End Sub

     Private Sub Command1_Click()
        ShowModalForm Form2
     End Sub

and change the Command1_Click event in Form2 to:

     Private Sub Command1_Click()
        ShowModalForm Form3
     End Sub

Now the forms correctly display and act like Modal forms, but the program does
not hang when Form3 is dismissed.

Additional query words: 4.00 vb4win vb4all buglist4.00

======================================================================
Keywords          :  kbbuglist
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400
Version           : 4.00
Issue type        : kbbug

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

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Q150206: BUG: DBGrid on a Modal Form Can Cause a Program to Hang