json_decode($str,true)的结果为null

        //$result为传进来的json值
        $result = $this->params['auth_result'];
       //html_entity_decode进行html 实体转换为字符
       //stripslashes() 函数的作用是删除反斜杠
        $info = stripslashes(html_entity_decode($result));
        $resultcode = json_decode($info,true);