Unloading Form from Within DBGrid Event Causes GPF

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

SYMPTOMS

When unloading a form from within an event of a Data Bound Grid control a General Protection fault will occur in VB.EXE or an Exception fault will occur in VB32.EXE.

CAUSE

The cause of the problem is that the unload event is destroying the recordset object of the data control. When the DBGrid gets control back the recordset pointer is no longer valid.

STATUS

Microsoft has confirmed this to be a problem in Visual Basic version 4.0. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

WORKAROUND

To work around this problem, add a timer control to the form and allow the "Unload Me" command to happen here rather than in the DBGrid control. Here is a step-by-step example to correct the problem:

1. Add a timer control to the form. Set its Enabled property to False and its Interval property to 5.

2. In the timer event of the timer control add 2 lines of code:

   Timer1.Enabled = False Unload Me

3. In the event of the DBGrid that you wish to unload the form add this line of code:

   Timer1.Enabled = True

MORE INFORMATION

Steps to Reproduce

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

2. Add a data control to Form1.

3. Set these properties of Data1:

      DatabaseName:      BIBLIO.MDB
      RecordSource:      Authors
   
   

4. Add a DBGrid control to the form.

5. Set this single property of DBGrid1:

      DataSource:      Data1
   
   

6. Add this line of code to the Click event of the DBGrid control:

      Private Sub DBGrid1_Click()
                Unload Me
      End Sub
   
   

7. Press F5 to run the project. Click the DBGrid. You will now get an Unhandled exception in VB32.EXE or a General Protection Fault in module DBGRID16.OCX at 0002:FB7F.