jQuery Grid Plugin - jqGrid

 How can i get the alert work  when i click the refresh button??????

jQuery("#list").navGrid('#pager',
            {edit:true, add:true, del:true, search:true, refresh:true}, 
            {   }, // edit options
            {   }, // add options
            {  }, //del options
            {  }, // search options
            {navkeys: [true,38,40], height:250, jqModal:false, closeOnEscape:true,
                           afterRefresh : function() {
                                                                alert('hello');    <------ this alert don't came up
                                                           }
 } );

thanks for you help...