Q173348: PRB: ActiveControl Set to "Nothing" on Disabled Form

Article: Q173348
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SYMPTOMS
========

In Microsoft Visual Basic version 4.0 for Windows, referencing the ActiveControl
property of a form that has been disabled returns the control. In Visual Basic
for Windows versions 5.0 and later, referencing the ActiveControl property of a
form that has been disabled causes run-time error 91 "Object variable or With
block variable not set" to be displayed.

CAUSE
=====

In Visual Basic 5.0 and later, the value of the ActiveControl property of a form
is set to "Nothing" when the form is disabled.

RESOLUTION
==========

The behavior is correct. This change in behavior may affect Visual Basic 4.0
applications that have been coded to the old behavior and then converted to
Visual Basic 5.0 or later. One workaround for this problem is to store the value
of the ActiveControl property in a variable before a form is disabled. That
variable can later be used to reference the control. To prevent the run-time
error from occurring, change the code to the following:

     Public Form2LastControl As Control 'General Declarations of Form1
     Private Sub Command1_Click()
     Set Form2LastControl = Form2.ActiveControl
     Form2.Enabled = False
     End Sub

     Private Sub Command2_Click()
     MsgBox Form2LastControl.Text
     End Sub

     Private Sub Form_Load() 'Form Load Event of Form1
     Form2.Show vbModeless
     End Sub

     Private Sub Form_Load() 'Form Load Event of Form2
     Set Form1.Form2LastControl = Me.Controls(0)
     End Sub

STATUS
======

This behavior is by design.

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

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

1. Create a new Visual Basic Standard EXE project. Form1 is created by default.

2. Add a form to the project (two forms are needed).

3. Place two command buttons on Form1. For example:

        Name: Command1, Caption: Disable Form 2
        Name: Command2, Caption: Active Control

4. Add the following code to Form1:

        Private Sub Command1_Click()
        Form2.Enabled = False
        End Sub

        Private Sub Command2_Click()
        MsgBox Form2.ActiveControl.Text
        End Sub

        Private Sub Form_Load()
        Form2.Show vbModeless
        End Sub

5. Place a TextBox control on Form2.

6. Run the project, and click on the "Active Control" command button.

7. You should see a message box that says "Text1."

8. Click on the command button labeled "Disable Form2."

9. Click on the command button labeled "Active Control."

10. Run-time error 91 "Object variable or With block variable not set" is
  displayed.

Additional query words: kbVBp kbdsd kbDSupport kbVBp500 kbVBp600 kbControl

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Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Issue type        : kbprb

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