來自：http://blog.csdn.net/vrhero/archive/2008/01/13/2042481.aspx

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///?<summary>
///?獲取一年中指定的一周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>
///?<param?name="first">當此方法返回時，則包含參數?year?和?weeks?指定的周的開始日期的?System.DateTime?值；如果失敗，則為?System.DateTime.MinValue。如果參數?year?或?weeks?超出有效范圍，則操作失敗。該參數未經初始化即被傳遞。</param>
///?<param?name="last">當此方法返回時，則包含參數?year?和?weeks?指定的周的結束日期的?System.DateTime?值；如果失敗，則為?System.DateTime.MinValue。如果參數?year?或?weeks?超出有效范圍，則操作失敗。該參數未經初始化即被傳遞。</param>
///?<returns>成功返回?true，否則為?false。</returns>
public?static?bool?GetDaysOfWeeks(int?year,?int?weeks,?CalendarWeekRule?weekrule,?out?DateTime?first,?out?DateTime?last)
{
????//初始化?out?參數
????first?=?DateTime.MinValue;
????last?=?DateTime.MinValue;

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

????//一年最多53周地球人都知道...
????if?(weeks?<?1?|?weeks?>?53)
????????return?false;

????//取當年首日為基準...為什么？容易得唄...
????DateTime?firstCurr?=?new?DateTime(year,?1,?1);
????//取下一年首日用于計算...
????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:
????????????????//不用解釋了吧...
????????????????first?=?firstCurr;
????????????????break;
????????????case?CalendarWeekRule.FirstFullWeek:
????????????????//順延一周...
????????????????first?=?first.AddDays(7);
????????????????break;
????????????case?CalendarWeekRule.FirstFourDayWeek:
????????????????//周首日距年首日不足4天則順延一周...
????????????????if?(firstCurr.Subtract(first).Days?>?3)
????????????????{
????????????????????first?=?first.AddDays(7);
????????????????}
????????????????break;
????????????default:
????????????????break;
????????}
????}

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

????//周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:
????????????????//周末日距下一年首日不足4天則提前一周...
????????????????if?(firstNext.Subtract(first).Days?<?4)
????????????????{
????????????????????first?=?first.AddDays(-7);
????????????????????last?=?last.AddDays(-7);
????????????????}
????????????????break;
????????????default:
????????????????break;
????????}
????}
????return?true;
}

總結

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