How to Validate Data by Using Customized Error Messages

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

When doing field-level validation on a form, you may want to use a custom error message and bypass the Visual FoxPro default error message such as "Invalid input." This article shows by example how to use custom error messages and turn off Visual FoxPro default error messages during field-level validation routines.

MORE INFORMATION

When designing validation routines as one of the active methods for a form's text boxes, developers often return a value of false (.F.) when the entered data fails the validation routine. Here is an example validation routine:

   If (M.Field <> "TEST")
      Wait Window "Incorrect Value"
      Return .F.
   Endif

To suppress the Visual Foxpro message, modify the field-level validation to return a value of zero (0). This turns off the FoxPro default error messages. Here's an example:

   If (M.Field <> "TEST")
      Wait Window "Incorrect Value"
      Return 0
   Endif

Code Sample

The following code example demonstrates this behavior. It uses a form and two text boxes. It also serves as a good example of how, in a program, you can define objects and add new objects to defined objects.

*--------------------------------------------------------------*

* Program: ValidTst - (C) 1995 - Microsoft Corporation         *
* This program demonstrates the difference between returning   *
* a value of false (.F.) when a field fails its validation     *

* leave the input field, you MUST enter the value of TEST.     *

frmMyForm = CREATEOBJECT('Form')              && Create a Form.
frmMyForm.Closable = .F.                      && Disable Control menu.

frmMyForm.AddObject('txtBox1','NewTextBox')   && Add 1st text box.
frmMyForm.AddObject('txtBox2','OldTextBox')   && Add 2nd text box.

frmMyForm.SHOW                                && Display the form.
READ EVENTS                                   && Start event processing.

* error message. The only thing you will see is the    *
* message box showing what you typed in.               *

  Visible = .T.
  Left    = 125
  Top     = 20

  PROCEDURE Valid
    IF (This.Value <> "TEST")
      =MessageBox("You entered: "+Alltrim(This.Value))
      RETURN 0                && Invalid data, do NOT return .f.
    ENDIF

*------------------------------------------------------*

* In the second text box, if you don't type in TEST,   *

* input) as well as the message box.                   *

  Visible = .T.
  Left    = 125
  Top     = 70

  PROCEDURE Valid
    IF (This.Value <> "TEST")
      =MessageBox("You Entered: "+Alltrim(This.Value))
      RETURN .F.             && Returning FALSE here.
    ENDIF

DEFINE CLASS cmdQuitButton AS CommandButton && Create command button.

    Caption = '\<Quit'       && Caption on the command button.
    Cancel  = .T.            && Default Cancel command button (Esc).
    Left    = 125            && command button column.
    Top     = 150            && command button row.
    Height  = 25             && command button height.
    Visible = .T.

    PROCEDURE Click
      CLEAR EVENTS           && Stop event processing, close Form.