PRB: Modal Form Flickers When Exiting Form with DBGrid Control

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

Under certain circumstances, unloading a form containing a DBGrid control causes Visual Basic to hang and other open forms to flicker. After hiding the third form of the program, the second form flickers or blinks. Under the 16-bit edition of Visual Basic, an application error follows the blinking, and displays the following error message:

   VB caused a general protection fault in module VB.EXE at 000b:000039f3.

CAUSE

The problem is limited to the following combination of circumstances:

• A project contains at least three forms with each form containing the DBGrid control.
• The first form shows a second, modal form. The problem does not occur if the second form is not shown modally.
• A single form creates two or more instances of the original form.

RESOLUTION

There are two possible resolutions to the problem. Either solution prevents the problem from occurring:

• Do not show the second form as a modal form.

  - or -

• In the Unload event of the third form, add the following line of code:

  Me.Enabled = False

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Problem

1. Create a Visual Basic project with three forms.

2. Add a Command button to Form1. Place the following code in the Click event of the Command button:

   Form2.Show 1

3. Add a Command button to Form2. Place the following code in the Click event of the Command button:

   Form3.Show 1

4. Add a DBGrid control to Form3. Run the project.

5. From Form1, click the Command button to show Form2. From Form2, click the Command button to show Form3. Close Form3.