求每个年,月,周的起始日期和结束日期

我们在写程序的时候往往要计算出年,月,周的开始日期和结束日期,在这里给出统一求解方法

/// <summary>
        /// 声明期间类型枚举
        /// </summary>
        public enum Period {Day, Week, Month, Year};
      /// <summary>
        /// 获取指定期间的起止日期
        /// </summary>
        /// <param name="period">期间类型</param>
        /// <param name="beginDate">开始日期</param>
        /// <param name="endDate">结束日期</param>
        public static void GetPeriod(Period period, out DateTime beginDate, out DateTime endDate)
        {
            int year = DateTime.Today.Year;
            int month = DateTime.Today.Month;
            switch (period)
            {
                case Period.Year: //年
                    beginDate = new DateTime(year, 1, 1);
                    endDate = new DateTime(year, 12, 31); 
                    break;
                case Period.Month: //月
                    beginDate = new DateTime(year, month, 1);
                    endDate = beginDate.AddMonths(1).AddDays(-1);
                    break;
                case Period.Week: //周
                    int week = (int)DateTime.Today.DayOfWeek;
                    if (week == 0) week = 7; //周日
                    beginDate = DateTime.Today.AddDays(-(week - 1));
                    endDate = beginDate.AddDays(6);
                    break;
                default: //日
                    beginDate = DateTime.Today;
                    endDate = DateTime.Today;
                    break;
            }
        }