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 if(ds.Tables[0].Rows.Count>0)

                {

                    this.DropDownList1.DataSource=ds;

                    this.DropDownList1.DataTextField="Order";

                    this.DropDownList1.DataBind();

                    ListItem li=new ListItem("---請選擇工單號碼---","");//以下兩行為插入新的Item

                    this.DropDownList1.Items.Insert(0,li);

                    this.Order_txt.Visible=false;

                    this.DropDownList1.Visible=true;

                }