Q269445: FIX: Unloading Form from Control Array Event Causes Error
Article: Q269445
Product(s): Microsoft Visual Basic for Windows
Version(s): 6.0 SP4
Operating System(s):
Keyword(s): kbVBp600 kbDSupport kbVS600sp4bug
Last Modified: 08-MAY-2002
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The information in this article applies to:
- Microsoft Visual Basic Learning Edition for Windows, version 6.0 SP4
- Microsoft Visual Basic Professional Edition for Windows, version 6.0 SP4
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 SP4
- Microsoft Visual Studio 6.0 SP4
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SYMPTOMS
========
You have a Visual Basic project that has a form with control array. You unload
the form inside of control array's event handler and when the form unloads, you
set the form to be Nothing. The project works fine with Visual Studio 6.0
Service Pack 3 installed. However, if Visual Studio 6. 0 Service Pack 4 is
installed on the computer, the application stops responding when the control
array's event to unload the form is fired.
RESOLUTION
==========
- To work around the problem for scenarios 1 and 2 (as described in the "More
Information" section of this article), don't set the form to nothing when the
form is unloaded.
- To work around the problem for scenario 3, make a form-level reference to the
form that will not lose scope while the form is active. To do so, add the
following to the General Declarations section:
Private f as Form
A supported fix is now available from Microsoft, but it is only intended to
correct the problem described in this article and should be applied only to
systems experiencing this specific problem. This fix may receive additional
testing at a later time, to further ensure product quality. Therefore, if you
are not severely affected by this problem, Microsoft recommends that you wait
for the next service pack that contains this fix.
To resolve this problem immediately, contact Microsoft Product Support Services
to obtain the fix. For a complete list of Microsoft Product Support Services
phone numbers and information about support costs, please go to the following
address on the World Wide Web:
http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS
NOTE: In special cases, charges that are normally incurred for support calls may
be canceled, if a Microsoft Support Professional determines that a specific
update will resolve your problem. Normal support costs will apply to additional
support questions and issues that do not qualify for the specific update in
question.
STATUS
======
Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.
MORE INFORMATION
================
There are at least three scenarios in which this bug appears.
Steps to Reproduce the Problem
------------------------------
Scenario #1
1. Create a Standard EXE Visual Basic Project under Visual Basic 6.0 with Visual
Studio 6 Service Pack 4 installed. Form1 is created automatically.
2. Press CTRL+T, and the add any non-intrinsic control into the components
dialog box. For example, add "Sheridan 3D Controls" or "Microsoft Windows
Common Controls 6.0 (SP4)".
3. Add an instance of SSCommand to Form1. Use the default name, which is
SSCommand1.
4. Create a control array by giving the control an index of 0.
5. Add the following code to Form1:
Private Sub Form_Unload(Cancel As Integer)
'The following line causes a fault under SP4, when 'Unload Me'
'is called from an event in a control array.
'Comment this out to work around the bug.
Set Form1 = Nothing
End Sub
Private Sub SSCommand1_Click(Index As Integer)
Unload Me
End Sub
6. Save the project, and press F5 to run it.
7. Click the command button. Visual Basic stops responding and displays the
following error message:
The instruction at "0x004051ba" referenced memory at "0x0000007a". The Memory
could not be "written".
8. Open the project in the Visual Basic integrated development environment
again.
9. Comment out the following line:
Set Form1 = Nothing
10. Save the project, and then press F5 to run it. Click the command button. The
form closes without a problem.
Scenario #2
1. Create a new UserControl.
2. Add the following code:
Public Event Click()
Private Sub UserControl_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
RaiseEvent Click
End Sub
3. From the File menu, select Add Project, and then select Standard EXE.
4. Press CTRL+R to display the Project Explorer.
5. Right-click Project1, and select Set as Start Up.
6. Double-click Form1 to open the Form Designer, and then drop an instance of
the newly created User Control on it. Use the default name of UserControl11.
7. Create a control array by giving the control an index of 0.
8. Add the following code:
Private Sub UserControl11_Click(Index As Integer)
Unload Me
End Sub
Private Sub Form_Unload(Cancel As Integer)
Set Form1 = Nothing
End Sub
9. Save the project and press F5 to run it.
10. Click the UserControl. Visual Basic fails and displays the following error
message:
The instruction at "0x004051ba" referenced memory at "0x0000007a". The Memory
could not be "written".
11. Open the project in Visual Basic again.
12. Comment out the line:
Set Form1 = Nothing
13. Save the project, and then press F5 to run it.
14. Click the UserControl. The form closes without a problem.
Scenario #3
1. Create a new Standard EXE.
2. Add a command button to Form1. Use the default name, which is Command1.
3. Add the following code:
Private Sub Command1_Click()
Dim f As New Form2
f.Show
End Sub
4. Add Form2 to the project.
5. Press CTRL+T, and then add any non-intrinsic control into the components
dialog box, such as "Sheridan 3D Controls" or "Microsoft Windows Common
Controls 6.0 SP4)".
6. Add an instance of SSCommand to Form2. Use the default name, which is
SSCommand1.
7. Create a control array by giving the control an index of 0.
8. Add the following code to Form2:
Private Sub SSCommand1_Click(Index As Integer)
Unload Me
End Sub
9. Save the project, and then press F5 to run it.
10. Click Command1. Form2 appears.
11. Click SSCommand1. Visual Basic stops responding and displays the following
with error message:
The instruction at "0x004051ba" referenced memory at "0x0000007a". The Memory
could not be "written".
12. Open the project in Visual Basic again.
13. Change the line
Dim f as New Form2
in Form1 to:
Set f = New Form2
Add the following code to the General Declarations section of Form1:
Private f as Form2
14. Save the project, and then press F5 to run it.
15. Click Command1. Form2 appears.
16. Click SSCommand1. The form closes without a problem.
Additional query words: 0x004051ba 0x0000007a
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Keywords : kbVBp600 kbDSupport kbVS600sp4bug
Technology : kbVSsearch kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVS600SP4 kbVB600SP4 kbVS600Search
Version : :6.0 SP4
Issue type : kbbug
Solution Type : kbfix
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