表头排序问题

*** demo.prg
PUBLIC oform1

SET PROCEDURE TO myclass.prg ADDITIVE

oform1=Newobject("frmDemo")
oform1.Show
RETURN

DEFINE CLASS frmDemo AS form
    Height = 352
    Width = 529
    DoCreate = .T.
    AutoCenter = .T.
    Caption = "Demo"
    Name = "frmDemo"

    ADD OBJECT Grd1 AS grd WITH ;
        DeleteMark = .F.,;
        Height = 336,;
        Left = 7,;
        Top = 9,;
        Width = 516,;
        Name = "Grd1"

    PROCEDURE Load
        set safety off
        Create Cursor Demo(编码 C(10),名称 C(20),价格 N(12,2),日期 D)
        Insert Into Demo(编码,名称,价格,日期) Values ("0001","华硕 F9S F9G233S-SL",7399,Date())
        Insert Into Demo(编码,名称,价格,日期) Values ("0002","戴尔 Vostro 1310(R520555)",6100,Date())
        Insert Into Demo(编码,名称,价格,日期) Values ("0003","Gateway T-6818c",5999,Date())
        Insert Into Demo(编码,名称,价格,日期) Values ("0004","海尔 S20-T2370G10160BgHQCFP",5999,Date())
        Insert Into Demo(编码,名称,价格,日期) Values ("0005","ThinkPad R61i 774227C",6400,Date())
        Insert Into Demo(编码,名称,价格,日期) Values ("0006","惠普 Compaq Presario V3803TX(KS396PA)",5700,Date())
        Go Top
    ENDPROC

    PROCEDURE Init
        This.grd1.Bind()
    ENDPROC
ENDDEFINE

*** myclass.prg
DEFINE CLASS grd AS grid
    Height = 200
    Width = 320
    issort = .T.
    sortgrc = ""
    Name = "grd"

    PROCEDURE grhclick
        If This.isSort = .F.
           Return
        Endif
        Local Array laEvents[1]
        Try
           Private lcSourceAlias,lcControlSource,lcField,lcTag,Ftag,lnBuffer,lcSortGrc
           Local lcSourceAlias,lcControlSource,lcField,lcTag,Ftag,lnBuffer,lcSortGrc
           Aevents(laEvents,0)   
           lcSourceAlias = laEvents[1,1].Parent.Parent.RecordSource
           lcControlSource = laEvents[1,1].Parent.ControlSource
           lcSourceAlias = Iif(!Empty(lcSourceAlias),lcSourceAlias,Substr(lcControlSource,1,At(".",lcControlSource)-1))
           lcSourceAlias = Iif(!Empty(lcSourceAlias),lcSourceAlias,Alias())
           lcField = Substr(lcControlSource,At(".",lcControlSource)+1)
           *--
           If Empty(lcSourceAlias)
              Return
           Endif
           If Empty(lcField)
              Return
           Endif
        
           lcTag = "SortTag"
           Ftag = This.GetFieldTag(lcSourceAlias,lcField)
           Select (lcSourceAlias)
           *--
           lnBuffer = CursorGetProp("Buffering")
           If lnBuffer > 3
              CursorSetProp("Buffering" ,3)
           Endif
           *--
           lcSortGrc = This.SortGrc
           If !Empty(This.SortGrc)
              This.&lcSortGrc..Header1.Picture=""
           Endif
           This.SortGrc= laEvents[1,1].Parent.Name
           
           Select(lcSourceAlias)
           If Empty(Ftag)
              If laEvents[1,1].Tag = "Down"
                 Inde On &lcField Tag &lcTag Descending
                 laEvents[1,1].Picture = Iif(File("Down.bmp"),"Down.bmp","")
                 laEvents[1,1].Tag = "Up"
              Else
                 Inde On &lcField Tag &lcTag Ascending
                 laEvents[1,1].Picture = Iif(File("Up.bmp"),"Up.bmp","")
                 laEvents[1,1].Tag = "Down"
              Endif
           Else
              If laEvents[1,1].Tag = "Down"
                 Set Order To (Ftag) Descending
                 laEvents[1,1].Picture = Iif(File("Down.bmp"),"Down.bmp","")
                 laEvents[1,1].Tag = "Up"
              Else
                 Set Order To (Ftag) Ascending
                 laEvents[1,1].Picture = Iif(File("Up.bmp"),"Up.bmp","")
                 laEvents[1,1].Tag = "Down"
              Endif
           Endif
           If lnBuffer > 3
              CursorSetProp("Buffering" ,lnBuffer)
           Endif
           Go Top
           This.Refresh
        Catch
        Endtry
    ENDPROC
        
    PROCEDURE bind
        Unbindevents(This)
        This.SetAll("MousePointer",1,"Header")
        For Each oControl In This.Columns
           Bindevent(oControl.Controls(1),"Click",This,"grhClick")
        Endfor
    ENDPROC
        
    PROCEDURE getfieldtag
        Lparameter tcAlias,tcField
        Local lnTags,lnI,lcKey,lcTag
        lcTag = ""
        If Used(tcAlias)
           lnTags = Tagcount("",tcAlias)
           For lnI = 1 To lnTags
              lcKey = Key("",lnI,tcAlias)
              If Upper(Alltrim(lcKey)) = Upper(Alltrim(tcField))
                 lcTag = Upper(Tag("",lnI,tcAlias))
                 Exit
              Endif
           Endfor
        Endif
        Return lcTag
    ENDPROC
ENDDEFINE