C# System.Threading.Timer 使用方法

public class TimerHelper
    {
        System.Threading.Timer timer;
        public TaskSendMMS tasksendmms { get; set; }
        public void Start()
        {
            timer = new System.Threading.Timer(new TimerCallback(tasksendmms.Execute), null, 100, 30000);
            tasksendmms.timer = timer; 
        }
    }

 public class TaskSendMMS
    {

        public Guid MMSId { get; set; }

        public Guid PhonePackageId { get; set; }

        public DateTime ExeTime { get; set; }

        private log log = new log();

        public System.Threading.Timer timer;

        public TaskSendMMS()
        {

        }
        public void Execute(object a)
        {
            try
            {
                log.writelog("=========================================開始執行計划========================================");
                string Extime = ExeTime.ToString("MM-dd HH:mm");
                string today = DateTime.Now.ToString("MM-dd HH:mm");
                if (today.Equals(Extime))//如果時間是執行時間,則執
                {
                    log.writelog("執行時間到了,時間為:" + today);
                    DataBase.DataClasses_MMSDataContext db = new DataBase.DataClasses_MMSDataContext();
                    var mms = db.MMS.Where(c => c.ID == this.MMSId).FirstOrDefault();
                    log.writelog("查詢數據庫MMS記錄名稱:" + mms.Title);
                    if (mms.State != 2) //如果該彩信 不是延遲發送的,直接退出.
                    {
                        log.writelog("該彩信不是延遲發送的,直接退出");
                        if (null != timer)
                        {
                            log.writelog("該彩信不是延遲發送的,直接退出 並關閉timer");
                            timer.Dispose();
                        }
                    }
                    else
                    {
                        log.writelog("執行時間到了,開始調用Web接口立即發送彩信.");
                        //發送彩信
                        Business.Start(this.MMSId.ToString(), this.PhonePackageId.ToString(), "");
                        log.writelog("調用接口成功,完成發送彩信.");
                        mms.State = 1;
                        db.SubmitChanges();
                        log.writelog("彩信狀態,修改為1");
                        if (null != timer)
                        {
                            log.writelog("全部完成 並關閉timer");
                            timer.Dispose();
                        }
                    }
                }
                else
                {
                    log.writelog("執行時間未到! 時間為: " + today);
                }
            }
            catch (Exception ee)
            {
                log.writelog("出現異常信息:" + ee.Message);
            }
            log.writelog("=========================================結束執行計划========================================");
        }
    }

/// <summary>
        /// 啟動執行計划 
        /// </summary>
        /// <param name="MmsId"></param>
        /// <param name="packageIDs"></param>
        /// <param name="datetime"></param>
        /// <returns></returns>
        public int StartSendMMs(string MmsId, string packageIDs, string datetime)
        {
            TimerHelper timer = new TimerHelper();
            timer.tasksendmms = new TaskSendMMS() { ExeTime = DateTime.Parse(datetime), MMSId = new Guid(MmsId), PhonePackageId = new Guid(packageIDs) };
            timer.Start();
            return 0;
        }