DateHelper

 public class DateHelper
    {
        #region 得到一周的周一和周日的日期
        /// <summary> 
        /// 计算本周的周一日期 
        /// </summary> 
        /// <returns></returns> 
        public static DateTime GetMondayDate()
        {
            return GetMondayDate(DateTime.Today);
        }
        /// <summary> 
        /// 计算本周周日的日期 
        /// </summary> 
        /// <returns></returns> 
        public static DateTime GetSundayDate()
        {
            return GetSundayDate(DateTime.Today);
        }
        /// <summary> 
        /// 计算某日起始日期（礼拜一的日期） 
        /// </summary> 
        /// <param name="someDate">该周中任意一天</param> 
        /// <returns>返回礼拜一日期，后面的具体时、分、秒和传入值相等</returns> 
        private static DateTime GetMondayDate(DateTime someDate)
        {
            int i = someDate.DayOfWeek - DayOfWeek.Monday;
            if (i == -1) i = 6;// i值 > = 0 ，因为枚举原因，Sunday排在最前，此时Sunday-Monday=-1，必须+7=6。 
            TimeSpan ts = new TimeSpan(i, 0, 0, 0);
            return someDate.Subtract(ts);
        }
        /// <summary> 
        /// 计算某日结束日期（礼拜日的日期） 
        /// </summary> 
        /// <param name="someDate">该周中任意一天</param> 
        /// <returns>返回礼拜日日期，后面的具体时、分、秒和传入值相等</returns> 
        private static DateTime GetSundayDate(DateTime someDate)
        {
            int i = someDate.DayOfWeek - DayOfWeek.Sunday;
            if (i != 0) i = 7 - i;// 因为枚举原因，Sunday排在最前，相减间隔要被7减。 
            TimeSpan ts = new TimeSpan(i, 0, 0, 0);
            return someDate.Add(ts);
        }
        #endregion

        #region 得到一月的月初和月末的日期
        /// <summary>
        /// 获得某日期月初
        /// </summary>
        /// <param name="someDate"></param>
        /// <returns></returns>
        public static DateTime GetMonthStart(DateTime someDate)
        {
            DateTime startMonth = someDate.Date.AddDays(1 - someDate.Day);  //本月月初
            return startMonth;
        }
        /// <summary>
        /// 获得某日期月末
        /// </summary>
        /// <param name="someDate"></param>
        /// <returns></returns>
        public static DateTime GetMonthEnd(DateTime someDate)
        {
            DateTime endMonth = someDate.Date.AddDays((someDate.Date.AddMonths(1) - someDate).Days - 1);  //本月月末
            return endMonth;
        }
        /// <summary>
        /// 获得本月月初
        /// </summary>
        /// <returns></returns>
        public static DateTime GetMonthStart()
        {
            return GetMonthStart(DateTime.Today);
        }
        /// <summary>
        /// 获得本月月末
        /// </summary>
        /// <returns></returns>
        public static DateTime GetMonthEnd()
        {
            return GetMonthEnd(DateTime.Today);
        }
        #endregion

        #region 得到一季度的季度初和季度末的日期
        /// <summary>
        /// 获得某日期季度初
        /// </summary>
        /// <param name="someDate"></param>
        /// <returns></returns>
        public static DateTime GetQuarterStart(DateTime someDate)
        {
            var dt = someDate.Date;
            DateTime startQuarter = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day);  //本季度初
            return startQuarter;
        }
        /// <summary>
        /// 获得某日期季度末
        /// </summary>
        /// <param name="someDate"></param>
        /// <returns></returns>
        public static DateTime GetQuarterEnd(DateTime someDate)
        {
            var dt = someDate.Date;
            DateTime startQuarter = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day);  //本季度初
            DateTime endQuarter = startQuarter.AddMonths(3).AddDays(-1);  //本季度末
            return endQuarter;
        }
        /// <summary>
        /// 获得本季度初
        /// </summary>
        /// <returns></returns>
        public static DateTime GetQuarterStart()
        {
            return GetQuarterStart(DateTime.Today);
        }
        /// <summary>
        /// 获得本季度末
        /// </summary>
        /// <returns></returns>
        public static DateTime GetQuarterEnd()
        {
            return GetQuarterEnd(DateTime.Today);
        }
        #endregion


        #region 得到一年的年初和年末日期
        /// <summary>
        /// 获得某日期年初
        /// </summary>
        /// <param name="someDate"></param>
        /// <returns></returns>
        public static DateTime GetYearStart(DateTime someDate)
        {
            DateTime startYear = new DateTime(someDate.Year, 1, 1);  //本年年初
            return startYear;
        }
        /// <summary>
        /// 获得某日期年末
        /// </summary>
        /// <param name="someDate"></param>
        /// <returns></returns>
        public static DateTime GetYearEnd(DateTime someDate)
        {
            DateTime endYear = new DateTime(someDate.Year, 12, 31);  //本年年末
            return endYear;
        }
        /// <summary>
        /// 获得本年年初
        /// </summary>
        /// <returns></returns>
        public static DateTime GetYearStart()
        {
            return GetYearStart(DateTime.Today);
        }
        /// <summary>
        /// 获得本年年末
        /// </summary>
        /// <returns></returns>
        public static DateTime GetYearEnd()
        {
            return GetYearEnd(DateTime.Today);
        }
        #endregion
    }