jQuery Grid Plugin - jqGrid

I downloaded the version 3.3 and I have a custom button when I show a PDF
I have this code:

    var url = urlString + "?oper=" + tipo;
             var postData = jQuery("#list").getGridParam('postData');
             url = url + "&_search=" + postData._search;
             url = url + "&searchField=" + postData.searchField;
             url = url + "&searchString=" + postData.searchString;
             url = url + "&searchOper=" + postData.searchOper;
            
             alert(url);
             window.open(url, "popup", "width=600,height=600");

             
but now the postData values are null...!             
Is there another variable or renamed fields ?