msdr[0]索引显示无法应用"MysqlDataReader"类型中，如何解决？

msdr[0]索引显示无法应用"MysqlDataReader"类型中

 internal class MySqlOpHelper
    {
        private string conStr = null;
        private MySqlConnection msc = null;
        private MySqlCommand msco = null;
        private MySqlDataReader msdr = null;
        // ⽤于系统登录 存储⽤户名和密码
        public Dictionary<string, string> dics = null;
        // ⽤于数据库查询后的数据对象List<StudentInfo>
        public List<Student> stus = null;
        public MySqlOpHelper(string conStr)
        {
            this.conStr = conStr ?? throw new ArgumentNullException(nameof(conStr));
        }
        /// <summary>
        /// 系统 登录
        /// </summary>
        /// <param name="opStr"></param>
        public void OpLoginMySql(string queryStr)
        {
            try
            {
                msc = new MySqlConnection(conStr);
                msc.Open();
                msco = new MySqlCommand(queryStr, this.msc);
                msdr = msco.ExecuteReader();
                dics = new Dictionary<string, string>();
                while (msdr.Read())
                {
                    dics.Add(msdr[0].ToString(), msdr[1].ToString());
                }
            }

调试下 msdr 返回列了没有，queryStr怎么写的