PRB: Cursor-Based Grid Goes Blank If SQL SELECT Resets Cursor

3.00    | 3.00b

The information in this article applies to:

• Microsoft Visual FoxPro for Windows, versions 3.0, 5.0, 5.0a
• Microsoft Visual FoxPro for Macintosh, version 3.0b

SYMPTOMS

If a grid's RecordSource property is set to a cursor, and then the SQL SELECT command resets the cursor, the grid appears blank if the RecordSource property is not set back to itself.

The following command will refresh the grid properly if a SQL SELECT is run to rebuild the cursor, but if the grid's column or header properties have been customized, these customized changes will be lost and the grid's column and header properties will change back to their default settings:

   THISFORM.GRID1.RECORDSOURCE=THISFORM.GRID1.RECORDSOURCE

   ARTICLE-ID: Q131836
   TITLE     : PRB: Grid Not Refreshing Displaying a Cursor from Query

CAUSE

When you rebuild the cursor that the grid is based on with the SQL SELECT command, the original cursor has to be destroyed before the new cursor can be created. When this happens, the grid columns and headers are also cleared and then recreated. Even when the grid's RecordSource is set back to itself, the custom settings of the grid's columns and headers are lost.

RESOLUTION

To refresh the grid without losing the custom properties of the columns and headers, set the RecordSource property to a dummy cursor that already has been created with the same fields as the cursor the grid is based on. After the SQL SELECT is run, change the RecordSource property back to the rebuilt cursor. This allows the properties of the columns and headers to remain intact while the cursor is being rebuilt.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Open the Customer.dbf table located in the \Vfp\Samples\Data directory, and create a form called GridForm.

2. Place the following code in the Load event of the form:

   SELECT cust_id, city, country FROM customer INTO CURSOR Temp1 SELECT cust_id, city, country FROM customer WHERE country = "" ;

         INTO CURSOR Temp2
   

3. Place the following code in the Destroy event of the form:

   SELECT Temp1 USE SELECT Temp2 USE

4. Place a grid on the form, and give the grid the following property settings:

   ColumnCount=3 RecordSourceType=Alias RecordSource=Temp1

5. Change the caption of the grid1.Column1.header1 to Customer Id and the Column1 Width property to 100.

6. Add a text box to the form.

7. Add a command button, and place the following code in its Click event:

   THISFORM.GRID1.RECORDSOURCE = "Temp2" SELECT cust_id, city, country FROM customer ;

         WHERE country = Thisform.text1.value ;
         INTO CURSOR Temp1
   

   THISFORM.GRID1.RECORDSOURCE = "Temp1"

8. Run the Form. Type Spain in the text box, and then click the command button. The grid should display all records where the country field is equal to Spain. Note that the name of the header of column 1 stays the same and the width of the column doesn't change. By changing the RecordSource of the grid to the cursor called Temp2, the properties of the columns and headers are not reset when the Temp1 cursor is rebuilt.

9. Change the two THISFORM.GRID1.RECORDSOURCE lines in the Click event of the command button into comments and add the following as the last line of code:

   THISFORM.GRID1.RECORDSOURCE = THISFORM.GRID1.RECORDSOURCE

   After running the form, typing a country name in the text box, and clicking the command button, note that the column name changes and the width is smaller.