combox 选择 只有两个值“是  否”如何做？

PUBLIC oform1

oform1=NEWOBJECT("form1")
oform1.Show
RETURN


    **************************************************
*-- Form:         form1 (e:\xp2\aaa.scx)
*-- 父类:  form
*-- 基类:    form
*-- 时间戳:   05/27/22 05:50:01 PM
*
DEFINE CLASS form1 AS form


    DoCreate = .T.
    Caption = "Form1"
    Name = "Form1"


    ADD OBJECT command1 AS commandbutton WITH ;
        Top = 108, ;
        Left = 108, ;
        Height = 25, ;
        Width = 96, ;
        Caption = "实时添加COMBO", ;
        Name = "Command1"


    ADD OBJECT command2 AS commandbutton WITH ;
        Top = 12, ;
        Left = 300, ;
        Height = 25, ;
        Width = 61, ;
        Caption = "顾得白", ;
        Name = "Command2"


    PROCEDURE command1.Click
        thisform.AddObject("Quantity",   "ComboBox")
        thisform.Quantity.Visible   =.T.
        thisform.Quantity.rowsource='是,否,YES,NO'
        thisform.Quantity.rowsourcetype=1 &&1=值
        thisform.Quantity.style=2 &&2=下拉列表框
        thisform.Quantity.left=this.Left+this.Width+2
        thisform.Quantity.top=this.top
        this.Enabled=.f.
    ENDPROC


    PROCEDURE command2.Click
        thisform.Release
    ENDPROC


ENDDEFINE
*
*-- EndDefine: form1
**************************************************

('是')
('否')
= 1