PRB: SET FILTER Command Behaves Differently in a Method or Event

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

SYMPTOMS

When you use the SET FILTER command to control data while in a form, most of the objects in the form disappear or do not display data properly after the SET FILTER command is issued. This problem occurs when you use a variable in the evaluation clause of the SET FILTER command and the command is executed in an object's method or event. Text and combo boxes may disappear while grids and list boxes do not show any records. Tabbing or clicking the location of the objects on the form restores them to their original values.

CAUSE

When you use a variable in a method or event, the variable goes out of scope unless the variable was available before the form was run.

RESOLUTION

• Use macro substitution in the SET FILTER command. An example is below:

     xyz = "'M'"             && Use double quotation marks outside of single
                             && quotation marks.
     SET FILTER TO <fieldname> = &xyz    && Using macro substitution.
  
  -or-
  
  

• Create the variable as public before you use it so that the variable does not go out of scope after leaving the event that it was created in.

STATUS

This behavior is by design.

MORE INFORMATION

Normally, a query would be used to create a subset of a table based on some value. The SET FILTER command can also be used to view that subset of data. Using a variable in the SET FILTER command in one of the object's methods or events is a problem because the variable goes out of scope after returning from the method or event. Therefore, the filter is invalid and the data resets back to all the records.

Trying to use a property of the form in the SET FILTER command results in this error:

   Property <property name> is not found.

Steps to Reproduce Behavior

1. Create a form with a text box and a list box.

2. Add a table into the form's DataEnvironment.

3. Set the following properties of the list box:

         RowSource = <tablename>
         RowSourceType = Alias
   

4. Set the ControlSource of the text box to a field in the table.

5. Create a command button and place the following code in the Click event:

         xyz = "M"  && Depending upon you filter, "M" is just an example.
         SET FILTER TO <fieldname> = xyz && Use a character field.
         Thisform.List1.Requery
         Thisform.Refresh
   

6. Run the form and click the command button. The text box may disappear and the list box has no records showing. Click each object to populate them with the original data.

7. Change the code in the Click event to one of the two options described in the Resolution section and run the form. The text and list box are now populated with the new data.