PRB: ActiveControl Set to "Nothing" on Disabled Form

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 5.0

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 version 5.0 for Windows, 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, the value of the ActiveControl property of a form is set to "Nothing" when the form is disabled.

RESOLUTION

The behavior in Visual Basic 5.0 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. 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 "Standard EXE" project in Microsoft Visual Basic 5.0.

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.
    

Keywords          : PrgCtrlsStd vb5all
Version           : WINDOWS:5.0
Platform          : WINDOWS
Issue type        : kbprb