$('#combox_role').combobox({

      panelHeight: ,

      url: '../../Handler/GetComboxItems.ashx?type=0',

      valueField: 'RoleId',

      textField: 'RoleName',

      onLoadSuccess: function () {

          var oData = $(this).combobox('getData');

          for (var item in oData[]) {

              if (item == "RoleId") {

                  $(this).combobox("select", oData[][item]);

              }

          }

      }

  });