注意：未定义的变量：在第75行的{/public/inc/logs_core.php中进行准备

Question

在运行日志时遇到以下错误，

  

注意：未定义的变量：准备   第75行上的/srv/users/inv/apps/inv/public/inc/logs_core.php致命   错误：在null中调用成员函数bind_param（）   /srv/users/inv/apps/inv/public/inc/logs_core.php，第75行

  public function count_logs($itemid, $catid, $userid) {
    if($itemid != false){
        $prepared = $this->prepare("SELECT COUNT(*) as c FROM invento_logs WHERE item=?", 'count_logs()');
        $this->bind_param($prepare->bind_param('i', $itemid), 'count_logs()');
    }elseif($catid != false){
        $prepared = $this->prepare("SELECT COUNT(*) as c FROM invento_logs WHERE item IN (SELECT id FROM invento_items WHERE category=?)", 'count_logs()');
        $this->bind_param($prepare->bind_param('i', $catid), 'count_logs()');
    }elseif($userid != false){
        $prepared = $this->prepare("SELECT COUNT(*) as c FROM invento_logs WHERE `user`=?", 'count_logs()');
        $this->bind_param($prepare->bind_param('i', $userid), 'count_logs()');
    }else{
        $res = $this->query("SELECT COUNT(*) as c FROM invento_logs", 'count_logs()');
        $obj = $res->fetch_object();

        return $obj->c;
    }

请指导我解决问题