Q150195: FIX: Hidden MDIChild Form Can Still Be Active Form

Article: Q150195
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001

-------------------------------------------------------------------------------
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 
-------------------------------------------------------------------------------

SYMPTOMS
========

Under certain circumstances, an MDIChild form can be hidden but still be the
active form. This occurs when an MDIChild form is shown before hiding the active
MDIChild form. The latter MDIChild form stays active although it is invisible.
Clicking in an area of the invisible form does not activate a visible form
behind it because the input is sent to the invisible form.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been fixed in Visual Basic 6.0.

WORKAROUND
==========

If you are going to hide an MDIChild form and then show another form, it is
important to hide the existing form first, and then show the new MDIChild form.

For example, instead of the code:

     Form3.Show

     Me.Hide

the following code accomplishes the same objective but avoids the problem
described above:

     Me.Hide

     Form3.Show

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

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

1. Start a new project in Visual Basic. Form1 is created by default. Select the
  Insert/Form menu option twice and insert an MDI parent form by selecting
  Insert/MDI Form.

2. Change the MDIChild property of all three regular forms to True. Place a
  Command button on Form1 and Form2. In the Click event of the Command button
  on Form1, place the following code:

     Private Sub Command1_Click()

        Form2.Show

     End Sub

3. In the Click event of the Command button on Form2, place the following code:

     Private Sub Command1_Click()

       Form3.Show

       Me.Hide

     End Sub

4. Run the project by pressing the F5 key. Click on the Command button of Form1
  to show Form2. Move Form2 so it only partially covers Form1. For example,
  have it cover the lower right hand corner of Form1. Click on the Command
  button on Form2 to show Form3 and hide Form2. Click on the lower right hand
  corner of Form1. Form1 is not activated.

To correct this problem, change the code in the Click event of the Command button
on Form2 to read:

     Private Sub Command1_Click()

        Me.Hide

     Form3.Show

     End Sub

Additional query words: kbVBp400bug kbVBp500fix kbVBp kbdsd kbDSupport kbNoKeyWord

======================================================================
Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400
Issue type        : kbbug
Solution Type     : kbfix

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.