how to post an array from extjs client and parsed by asp.net mvc

1.in client page:
 even data is stored in model,but since we use the 「Ext.JSON.encode」,have to trim
before we send ,for example:
===============================================
                   var arrSubmit = new Array();
                   for (var i = 0; i < gridSelected.getStore().getCount() ; i++) {
                       var rec = gridSelected.getStore().getAt(i);
                       var rec2Send = {
                           COS_CODE: rec.get('COS_CODE'),
                           COS_NAME: rec.get('COS_NAME'),
                           SBJ_CODE: rec.get('SBJ_CODE'),
                           SBJ_NAME: rec.get('SBJ_NAME'),
                           GRP_CODE: rec.get('GRP_CODE'),
                           GRP_NAME: rec.get('GRP_NAME'),
                           GRP_DTL: rec.get('GRP_DTL'),
                           TTL_SLOT: rec.get('TTL_SLOT'),
                           SELECTED: rec.get('SELECTED')
                       };
                       arrSubmit.push(rec2Send);
==============in the ajax request  function==============
                       Ext.Ajax.request({
                       url: "......your url to handle the request....",
                       method: 'POST',
                       params: {
                           dateString: timeStamp,
                           recsInString: Ext.JSON.encode(arrSubmit).replace(/<br\/>/g,"\\n")
                             
                       },
                       success: function (response) {
                           alert("Error: " - response.responseText);
                       },
                       failure: function (response) {
                           alert("Error: " - response.responseText);
                       }
                   });
================at server side,how it receive===========================
        public JsonResult RcvPreRegSubjGrp(string dateString,string recsInString) {

            List<MdlCosSbjGrpDtl> recs = JsonConvert.DeserializeObject<List<MdlCosSbjGrpDtl>>(recsInString);
               
            for (int i = 0; i < recs.Count ;i++ )
            {
                util.SqlLog.writeLog(dateString+" recieved pre-reg data is ",
                      recs[i].toLogString()
                    );
            }
        ....
        .....
         ....
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以上