搞個周計劃，資料庫設計只有年和周，客戶還要看日期。。

木有辦法，自己寫來不及，網上找了段程式碼自己改了改。。

廢話不多說，上程式碼。。

        // <summary>
        /// 獲取一年中指定的一週的開始日期和結束日期。開始日期遵循ISO 8601即星期一。
        /// </summary>
        /// <remarks>Write by vrhero</remarks>
        /// <param name="year">年（1 到 9999）</param>
        /// <param name="weeks">周（1 到 53）</param>
        /// <param name="weekrule">確定首周的規則</param>
        /// <returns>成功返回 true，否則為 false。</returns>
        public bool GetDaysOfWeeks(int year, int weeks, CalendarWeekRule weekrule)
        {
            //初始化引數
            DateTime first = DateTime.MinValue;
            DateTime last = DateTime.MinValue;

            //不用解釋了吧
            if (year < 1 | year > 9999)
                return false;

            //一年最多53周
            if (weeks < 1 | weeks > 53)
                return false;

            //取當年首日為基準
            DateTime firstCurr = new DateTime(year, 1, 1);
            //取下一年首日用於計算
            DateTime firstNext = new DateTime(year + 1, 1, 1);

            //將當年首日星期幾轉換為數字 星期日特別處理 ISO 8601 標準 
            int dayOfWeekFirst = (int)firstCurr.DayOfWeek;
            if (dayOfWeekFirst == 0) dayOfWeekFirst = 7;

            //得到未經驗證的周首日
            first = firstCurr.AddDays((weeks - 1) * 7 - dayOfWeekFirst + 1);

            //周首日是上一年日期的情況
            if (first.Year < year)
            {
                switch (weekrule)
                {
                    case CalendarWeekRule.FirstDay:
                        first = firstCurr;
                        break;
                    case CalendarWeekRule.FirstFullWeek:
                        //順延一週
                        first = first.AddDays(7);
                        break;
                    case CalendarWeekRule.FirstFourDayWeek:
                        //周首日距年首日不足4天則順延一週
                        if (firstCurr.Subtract(first).Days > 3)
                        {
                            first = first.AddDays(7);
                        }
                        break;
                    default:
                        break;
                }
            }

            //得到未經驗證的週末日
            last = first.AddDays(7).AddSeconds(-1);

            //週末日是下一年日期的情況
            if (last.Year > year)
            {
                switch (weekrule)
                {
                    case CalendarWeekRule.FirstDay:
                        last = firstNext.AddSeconds(-1);
                        break;
                    case CalendarWeekRule.FirstFullWeek:
                        //不用處理
                        break;
                    case CalendarWeekRule.FirstFourDayWeek:
                        //週末日距下一年首日不足4天則提前一週
                        if (firstNext.Subtract(first).Days < 4)
                        {
                            first = first.AddDays(-7);
                            last = last.AddDays(-7);
                        }
                        break;
                    default:
                        break;
                }
            }
            return true;
        }