获取上周一的方法和获取上个月第一天和最后一天的方法

        /// <summary>
        /// 中式的获取上周一的方法
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="weekday"></param>
        /// <returns></returns>
        public DateTime getWeekUpOfDate(DateTime dt, DayOfWeek weekday)
        {
            int intWeekday = Convert.ToInt32(weekday.ToString("d"));
            //因为C#提供的枚举中周日是0，所以这时候应该单独处理改为7，计算公式就是(n+6)
            if (intWeekday==0)
            {
                intWeekday = 7;
            }
            dt = dt.AddDays(-(intWeekday+6));
            return dt;
        }

        /// <summary>
        /// 获取上个月一号的时间
        /// </summary>
        /// <param name="datetime"></param>
        /// <returns></returns>
        private DateTime FirstDayOfPreviousMonth(DateTime datetime)
        {
            return datetime.AddDays(1 - datetime.Day).AddMonths(-1);
        }

        /// <summary>
        /// 获取上个月最后一天的时间
        /// </summary>
        /// <param name="datetime"></param>
        /// <returns></returns>
        private DateTime LastDayOfPrdviousMonth(DateTime datetime)
        {
            return datetime.AddDays(1 - datetime.Day).AddDays(-1);
        }