Js-datatable Unable to send Ajax

Ajaxjsphpdatatable

 JS脚本如下：服务端：public function lists()    {        $pri = self::_check_pri(array(44,59,66));        **$ajax = getgpc('ajax','G');**        //接收待查询、显示的数据库字段        $select_keys = array(' ', 'pay_id','transaction_type','transaction_id','receiver_id','pay_type','pay_money','pay_date','order_state','order_money','order_id','order_date','check_date','buyer_id');        // ajax请求        if ($ajax) {            if (!is_array($pri) || (!$pri[44] && !$pri[66])) {                exit;            }            $pay_hide = 0;            if ($pri[59]) {                $pay_hide = 1;            }            self::_lists_ajax($select_keys, $pay_hide);        }                现象：在服务端打印$ajax为NULL，不懂得该如何调试从前端到服务端过程中是否有ajax通信

