如何使用TComboBoxEx.Data属性

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, DB, ADODB, StdCtrls, ComCtrls, DBCtrls;type
  TForm1 = class(TForm)
    ADOConnection1: TADOConnection;
    ADOQuery1: TADOQuery;
    Button1: TButton;
    ComboBoxEx1: TComboBoxEx;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
  TComboExItemEx=class(TComboExItem)
    public
      value:string;
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
var
  cc:TComboExItem;
  p:pointer;
begin
  comboboxex1.Clear;
  adoquery1.Close;
  adoquery1.SQL.Clear;
  adoquery1.SQL.Add('SELECT jczbm, jczmc FROM  a_dw');
  adoquery1.Open;
  adoquery1.First;
  while not adoquery1.Eof do
  begin
    getmem(p,length(adoquery1.FieldByName('jczbm').AsString));
    p:=pwidechar(adoquery1.FieldByName('jczbm').AsString);
    cc:=comboboxex1.ItemsEx.Add();
    cc.Caption:=adoquery1.FieldByName('jczmc').AsString ;
    cc.Data:=p;
    adoquery1.Next;
  end;end;procedure TForm1.Button2Click(Sender: TObject);
var
  cc:TComboExItem;
  s:string;
  p:pchar;
begin
 cc:=comboboxex1.ItemsEx.ComboItems[comboboxex1.ItemIndex];
 p:=cc.Data;
 s:=p;
 showmessage(s);
 showmessage(inttostr(comboboxex1.ItemIndex));
end;end.
为什么驴唇不对马嘴？jczbm和jczmc不对应？