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Q139972: FIX: File Open Common Dialog in Win95 Returns Invalid Filename

Article: Q139972
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0,95
Operating System(s): 
Keyword(s): kbVBp400bug kbOSWin95 kbOSWin98fix kbGrpDSVB
Last Modified: 07-JUN-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 
- Microsoft Windows 95 
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SYMPTOMS
========

Calling the ShowOpen method of the common dialog control to show the File Open
common dialog box results in the following error:

  Run-time error '20477'
  Invalid filename

CAUSE
=====

This error occurs the second time the ShowOpen method is called after multiple
file names have been previously selected in the File Open dialog box. The only
time this error occurs is when the Flags property of the common dialog box
includes both cdlOFNAllowMultiselect (to allow multiple selections) and
cdlOFNExplorer (to use the Windows Explorer File Open dialog box). Without the
new shell, Microsoft Windows NT does not display the Windows Explorer Open File
dialog box, so this problem only occurs with Microsoft Windows 95.

In this case, clicking multiple files in the File Open dialog box and clicking
Open causes the FileName property of the common dialog control to be filled with
a NULL delimited string of filenames. When the ShowOpen method is called, an
attempt is made to set the default file(s) to whatever the FileName property of
the common dialog control is. The error results because the common dialog
control does not know what to do when it encounters embedded NULLs in the
FileName property.

RESOLUTION
==========

NULLs must be used instead of spaces to delimit the list of file names because
the Windows Explorer style Open File common dialog box with multiple selections
enabled automatically includes support for long filenames. However, because the
Open File dialog box does not accept a list of NULL delimited files when it is
displayed, there is no way to have multiple files selected by default when
displaying the Open File dialog box.

Use either of the following methods to avoid the error described above:

In your code, before the ShowOpen method is called again, reset the FileName
property of the common dialog box to a single file or to no file at all.

- or -

Do not use the cdlOFNAllowMultiselect and cdlOFNExplorer flags at the same time.
Search on "CommonDialog control," Topic: "Changes to CommonDialog Flags for
Windows 95 and Windows NT," in the Visual Basic Help file for more information
on the behavior of different combinations of these constants under different
operating systems.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of the article. This problem has been fixed in Microsoft Windows 98.

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

Steps to reproduce problem (under Windows 95 only)
--------------------------------------------------

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

2. In the toolbox, double-click CommonDialog to add a common dialog control to
  the form.

3. In the toolbox, double-click the command button to add a new command button
  to the form.

4. Add the following code to the Command1_Click procedure:

        Private Sub Command1_Click()
           CommonDialog1.Flags = cdlOFNAllowMultiselect Or cdlOFNExplorer
           CommonDialog1.ShowOpen
        End Sub

5. On the Run menu, click Start or press the F5 key to run your application.

6. Click the command button and in the resulting File Open dialog box select two
  or more files. Click Open to hide the File Open dialog box.

7. Click the command button again to attempt to show the File Open dialog box
  again. Instead of the dialog box, a message box showing the above mentioned
  error is displayed.

REFERENCES
==========

Visual Basic for Windows Help file version 4.0; Search on "CommonDialog
control,"; Topic: "Changes to CommonDialog Flags for Windows 95 and Windows
NT,".

Additional query words: kbCtrlz

======================================================================
Keywords          : kbVBp400bug kbOSWin95 kbOSWin98fix kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbWin95search kbVB400Search kbVB400 kbZNotKeyword3 kbVB16bitSearch
Version           : WINDOWS:4.0,95
Issue type        : kbbug
Solution Type     : kbfix

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