How to add a class to a new row in a jquery datatables?

How can I add a class to the row I'm adding in the datatable?

If not possible, how can I use fnRowCallback or fnDrawCallback to change the class?

oTable = $('#example').dataTable( {
  "bJQueryUI": true,
  "bSortClasses": false,
  "sDom":'T<"clear">',
  "sPaginationType": "full_numbers",
  "sDom": 'T<"clear"><"fg-toolbar ui-widget-header ui-corner-tl ui-corner-tr ui-helper-clearfix"lfr>t<"fg-toolbar ui-widget-header ui-corner-bl ui-corner-br ui-helper-clearfix"ip>',
  "fnRowCallback": function( nRow, aData, iDisplayIndex ) {

    var oSettings = oTable.fnSettings();
    oSettings.aoData[iDisplayIndex].nTr.className = "gradeX odd";
  }
});

The above code is giving me an error.

this is how I add the row:

oTable.fnAddData(arr);