PRB: Incremental Search with Grid Causes Screen Flicker

• Microsoft Visual FoxPro 5.0 for Windows

SYMPTOMS

The Refresh method of the Grid control does not move the record pointer in the grid to the selected record when the record pointer is moved from a control external to the grid. The grid has to get the focus in order for the record pointer in it to move to the selected record. Because of this problem, an incremental search routine, involving the grid and another control, causes the screen to flicker every time a character is entered.

This article describes a way to avoid the screen flicker when using an incremental search routine with a grid.

WORKAROUND

You can use the LockScreen property of the Form to eliminate most of the screen flicker. For example, you can make the following modifications to the Form created in the STEPS TO REPRODUCE BEHAVIOR section below:

1. Create a New Property for the Form and name it lRefreshingGrid. Set the property to .F.

2. Change the code in Text1.InterActiveChange event as follows:

         ThisForm.lRefreshingGrid = .T.
         ThisForm.LockScreen = .T.
         SELECT customer
         SEEK UPPER(ALLTRIM(ThisForm.Text1.Value))
         ThisForm.grid1.SetFocus
         ThisForm.text1.SetFocus
         ThisForm.LockScreen = .F.
         ThisForm.lRefreshingGrid = .F.
   

3. To ensure that the Valid event of the text box does not fire when the focus is moved to the grid and then back to the text box, add the following code to the Valid event of the text box:

         IF ThisForm.lRefreshingGrid
            RETURN .T.
         ENDIF
   
   

STATUS

Microsoft is researching this behavior and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a Form, and set the LockScreen property to False (.F.).

2. Add the Customer table, in the home()+"SAMPLES\DATA" folder, to the Data Environment.

3. Drag the table onto the form to create a grid.

4. Add a TextBox control to the form. Make sure that SelectOnEntry property of the Textbox control is set to .F. (the default). Add the following code to the TextBox control's InterActiveChange event:

         SELECT customer
         SEEK UPPER(ALLTRIM(ThisForm.Text1.Value))
         ThisForm.Grid1.Refresh
   

5. Run the Form and type a few characters in the text box.

6. Although the REFRESH method of the grid is being called from Text1.InterActiveChangeEvent, the record pointer in the grid does not move to the correct record.

7. Now change the code in Text1.InterActiveChange event as follows:

         SELECT customer
         SEEK UPPER(ALLTRIM(ThisForm.Text1.Value))
         ThisForm.grid1.SetFocus
         ThisForm.text1.SetFocus
   

8. Repeat step 5.

9. Now the Record Pointer in the grid is moving correctly but there is a lot of screen flicker every time a character is entered into the text box.