/// <summary>

        /// 取得某月的第一天

        /// </summary>

        /// <param name="datetime">要取得月份第一天的时间</param>

        /// <returns></returns>

        private DateTime FirstDayOfMonth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day);

        }

         <summary>

        /// 取得某月的最后一天

        /// </summary>

        /// <param name="datetime">要取得月份最后一天的时间</param>

        /// <returns></returns>

        private DateTime LastDayOfMonth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddMonths(1).AddDays(-1);

        }

         <summary>

        /// 取得上个月第一天

        /// </summary>

        /// <param name="datetime">要取得上个月第一天的当前时间</param>

        /// <returns></returns>

        private DateTime FirstDayOfPreviousMonth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddMonths(-1);

        }

         <summary>

        /// 取得上个月的最后一天

         /// </summary>

        /// <param name="datetime">要取得上个月最后一天的当前时间</param>

        /// <returns></returns>

        private DateTime LastDayOfPrdviousMonth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddDays(-1);

        }