FoxPro/Visual FoxPro - Como validar informacion de un combobox desde un prg en vfp 9

SET SYSMENU TO

SET SYSMENU AUTOMATIC

DEFINE PAD _0k50sa3dr OF _MSYSMENU PROMPT "\<Window" COLOR SCHEME 3 ;

    KEY ALT+W, ""

DEFINE PAD _0k50sa3ds OF _MSYSMENU PROMPT "E\<xit" COLOR SCHEME 3 ;

    KEY ALT+X, ""

ON PAD _0k50sa3dr OF _MSYSMENU ACTIVATE POPUP Wwindow

ON SELECTION PAD _0k50sa3ds OF _MSYSMENU DO CloseDemo

DEFINE POPUP Wwindow MARGIN RELATIVE SHADOW COLOR SCHEME 4

DEFINE BAR 1 OF Wwindow PROMPT "\<Close" ;

    SKIP FOR TYPE("_Screen.ActiveForm.Name")<>"C"

DEFINE BAR 2 OF Wwindow PROMPT "\<Open"

ON SELECTION BAR 1 OF Wwindow =_SCREEN.ACTIVEFORM.RELEASE()

ON SELECTION BAR 2 OF Wwindow DO OpenForm

PUBLIC ARRAY aoForms(1)

aoForms[1] = NEWOBJECT("frmdemo")

aoForms[1].SHOW

READ EVENTS

SET SYSMENU TO DEFAULT

CLEAR ALL

    PROCEDURE OpenForm

    DIMENSION aoForms(ALEN(aoForms)+1)

    aoForms[ALEN(aoForms)] = NEWOBJECT("frmdemo")

    aoForms[ALEN(aoForms)].SHOW

    RETURN

    PROCEDURE CloseDemo

    CLEAR EVENTS

    RETURN

DEFINE CLASS frmdemo AS FORM

    CAPTION = "Demo Form"

    NAME = "frmDemo"

    ADD OBJECT cmdClose AS COMMANDBUTTON WITH ;

        TOP = 200, ;

        LEFT = 264, ;

        HEIGHT = 27, ;

        WIDTH = 84, ;

        CANCEL = .T., ;

        CAPTION = "Close", ;

        DEFAULT = .T., ;

        NAME = "cmdClose"

    PROCEDURE cmdClose.CLICK

    m.nOKButton=0

    m.nInfo=64

    =MESSAGEBOX("After this Form closes, select Exit from the menu to return to the Command Window",m.nInfo+m.nOKButton)

    THISFORM.RELEASE

ENDPROC

    PROCEDURE RELEASE

    LOCAL m.nIndex

    FOR m.nIndex = 1 TO ALEN(aoForms)

        IF VARTYPE(aoForms[m.nIndex])=="O"

            IF aoForms[m.nIndex]=THIS

                aoForms[m.nIndex] = ""

                EXIT

            ENDIF

        ENDIF

    ENDFOR

ENDPROC

ENDDEFINE