phpcms怎么判断用户是否登录

<?php
        $userid= param::get_cookie('_userid');
?>

{if $userid}   
       。。。这里写已经登录之后的代码。。。
{else}
{/if}

<?php 
defined('IN_PHPCMS') or exit('No permission resources.');
class MY_index extends index {
    private $times_db;
    public function __construct() {
        parent::__construct();
    }
	public function top_mini() {
		$_username = param::get_cookie('_username');
		$_userid = param::get_cookie('_userid');
		$siteid = isset($_GET['siteid']) ? intval($_GET['siteid']) : '';
		$jsoncallback=isset($_GET['jsoncallback']) ? $_GET['jsoncallback'] : '';
		//定义站点id常量
		if (!defined('SITEID')) {
		   define('SITEID', $siteid);
		}
		if($_username){
			$res["success"]=1;
			$res["message"]='  '.L('hellow').'<a href="'.APP_PATH.'member-account_manage_avatar.html" target="_blank">;@@##@@;</a>; '.get_nickname().' 欢迎回家 <a href="'.APP_PATH.'member-index.html" target="_blank">;'.L('member_center').'</a>; | <a href="'.APP_PATH.'member-fabu.html" target="_top" class="upv_btn">;发布信息</a>; | <a href="'.APP_PATH.'member-logout.html">;'.L('logout').'</a>;';
			$res["message"] = pc_base::load_config('system', 'charset') == 'gbk' ? iconv('utf-8', 'utf-8', $res["message"]) : $res["message"];
			//get_nickname();//,
			
			}
		else{
			$res["success"]=0;
			}
			
		if($jsoncallback){
      		echo $jsoncallback . "({\"items\":[".json_encode($res)."]})";
		}else{
			echo json_encode($res);
		}
		//echo json_encode($res);
	}

}
?>