PRB: Handling Violation of Field Rules in Forms

The information in this article applies to:

• Microsoft Visual FoxPro for Windows, version 5.0

SYMPTOMS

If the REVERT or HELP buttons are not desirable in the dialog box that Visual FoxPro 5.0 presents for violations of Field Rules, it is possible to trap the error and present a custom dialog box. These errors were not trappable in either Visual FoxPro 3.0 or 3.0b.

RESOLUTION

There are basically three potential workarounds for this situation:

The first can be with or without the use of classes. Using classes, however, is recommended and the implementation below allows you to use the workaround on a form not using any custom classes.

1. Create a custom Form Property called lFlagError.

2. In the Error Method of the Form, add the following code:

         IF nError = 1582 && Field "name" validation rule is violated
            THIS.lFlagError = .T.
         ENDIF
   
   

3. In the LOSTFOCUS of any TextBox that is based on a field with a field rule, add the following code:

         IF THISFORM.lFlagError
            NODEFAULT && Do not move Focus to Next Object
            THISFORM.lFlagError = .F.
         ENDIF
   
   

   Current Rule: .NOT. EMPTY(<fieldname>)

   Modified Rule*: MyCustomRule()
   *Best placed in Store Procedures of the Database container

   FUNCTION MyCustomRule()
      IF EMPTY(<fieldname>)
         REPLACE <fieldname> WITH ;
         EVAL(DBGETPROP('<alias.fieldname','FIELD','DEFAULTVALUE'))
      ENDIF

1. From the File menu, click New, and then click Class.

2. From the "Based On" combo box click Timer (for a name, use ErrTimer).

3. Choose a Class library to store the class in and click OK.

4. From the Class menu, click Property and name it - oObjRef.

5. In the Timer Method, enter the following code:

         && Turn the Timer back off
         THIS.INTERVAL = 0
   

         && Tell the user there was an error
         =MESSAGEBOX(MESSAGE(),48)
   

         && Put the user back in the control
         THIS.oObjRef.SETFOCUS()
         THIS.oObjRef=.NULL.
   

6. Create a form.

7. Add the following code to the form's ERROR method:

         && Check and see if the error was due to Rule Validation
         IF nError = 1582
   

            && Store an object reference of the Current Control to the
            && custom property oObjRef
            THIS.Errtimer1.oObjRef = THIS.ACTIVECONTROL
   
            && The interval can be critical, setting it to low and timing
            && problems occur, such as the Timer's custom property
            && not getting set.
            THIS.Errtimer1.INTERVAL = 100
         ENDIF
   
   

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Issue the following commands in the Command window:

         CREATE DATABASE beakrul
         CREATE TABLE tTemp ;
           (cFld1 c(3) CHECK .NOT. EMPTY(cFld1) ERROR 'Cannot be empty!')
         CREATE FORM breakrul
   
   

2. Set the Form's BUFFERMODE to "2 - Optimistic."

3. Right-click on the form and click "Data Environment."

4. Right-click in the DataEnvironment Window and click "Add Table."

5. Select the above table.

6. Click Close to close the "Add Table or View" dialog box.

7. Click on a field in the Data Environment window and drag it onto the form.

8. Add a CommandButton to the Form.

9. Double-Click on the CommandButton.

10. In the CommandButton's CLICK method add the following code:

           APPEND BLANK
           THISFORM.REFRESH()
    

11. Save and run the form.

12. Click on the CommandButton.

13. Tab to the TextBox.

14. Type anything in the TextBox and hit Enter

15. Tab back to the TextBox.

16. Delete the contents of the TextBox and press Enter. The Field Validation dialog box appears.

REFERENCES

For more information about replacing values from field rules, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q158255
   TITLE     : How To Modify a Rule's Table to Which It Belongs in VFP 5.0