在组合框中的到焦点时自动打开下拉框，在组合文本框中输入字符时，能在下拉框中自动模糊定位并选择数据？如何实现？

PUBLIC oform1

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

DEFINE CLASS form1 AS form
    DoCreate = .T.
    Caption = "Form1"
    Name = "Form1"
    ADD OBJECT combo1 AS combobox WITH ;
        Height = 24, ;
        Left = 36, ;
        TabIndex = 2, ;
        Top = 36, ;
        Width = 100, ;
        Name = "Combo1"
    ADD OBJECT text1 AS textbox WITH ;
        Height = 20, ;
        Left = 36, ;
        TabIndex = 1, ;
        Top = 12, ;
        Width = 100, ;
        Name = "Text1"
    ADD OBJECT text2 AS textbox WITH ;
        Height = 20, ;
        Left = 36, ;
        TabIndex = 3, ;
        Top = 84, ;
        Width = 100, ;
        Name = "Text2"
    PROCEDURE Init
        CREATE CURSOR tt (xm c(10))
        INSERT INTO tt VALUES ("语文")
        INSERT INTO tt VALUES ("语文1")
        INSERT INTO tt VALUES ("语文2")
        INSERT INTO tt VALUES ("数学")
        INSERT INTO tt VALUES ("数学1")
        INSERT INTO tt VALUES ("数学2")
    ENDPROC

    PROCEDURE combo1.InteractiveChange
        cValue=ALLTRIM(This.Text)
        SELECT xm FROM tt WHERE cValue$xm INTO CURSOR cx
        WITH
            .Rowsource="cx"
            .RowsourceType=2
            .Requery
        ENDWITH
        **KEYBOARD "{F4}" && 自动弹开下拉框，使用不方便
    ENDPROC

ENDDEFINE

谢谢你的回复！我是想为了方便输入，在下拉列表中项特别多，一项项找太麻烦，可以在文本框中输入在下接列表框中模糊定位，其实代吗我会写，可是不知道怎么灵活的控制下拉框的打开的关闭！在组合框中如何引用文本框的下拉列表本身呢？

用 textbox + listbox 自己封装一个