combox 绑定数据后增加item

//给楼道好下拉框初始化      

   private void InitCmb_dh()       

  {           

  AccessDbHelper.ConnectionString = ConfigurationManager.ConnectionStrings["acc"].ConnectionString;  //连接字符   

          string sql = "select  楼栋代码,楼栋名称 from 楼栋表 where 管理单位='" + globeInfo.g_OfficeCode + "' ";     

            DataSet ds2 = AccessDbHelper.Query(sql);

            DataTable dt = new DataTable();

            dt = ds2.Tables[0];

            DataRow dr = dt.NewRow();

            dr[0] = "0";

            dr[1] = "所有楼栋";  

            dt.Rows.InsertAt(dr, 0);

            cmb_system.DataSource = dt;

            cmb_system.DisplayMember = "楼栋名称";     

            cmb_system.ValueMember = "楼栋代码";     

    }