获取本周指定周几的日期

/// <summary>
        /// 获取本周指定周几的日期
        /// </summary>
        /// <returns></returns>
        public string GetThisWeekMonday(System.DayOfWeek dw)
        {
            DateTime firstDate;
            DateTime date;
            dtpBeginTime.Value = firstDate = date = Client.SystemDate;
            switch (date.DayOfWeek)
            {
                case System.DayOfWeek.Monday:
                    firstDate = date;
                    break;
                case System.DayOfWeek.Tuesday:
                    firstDate = date.AddDays(-1);
                    break;
                case System.DayOfWeek.Wednesday:
                    firstDate = date.AddDays(-2);
                    break;
                case System.DayOfWeek.Thursday:
                    firstDate = date.AddDays(-3);
                    break;
                case System.DayOfWeek.Friday:
                    firstDate = date.AddDays(-4);
                    break;
                case System.DayOfWeek.Saturday:
                    firstDate = date.AddDays(-5);
                    break;
                case System.DayOfWeek.Sunday:
                    firstDate = date.AddDays(-6);
                    break;
            }
            DateTime dt = firstDate;
            switch (dw)
            {

                case System.DayOfWeek.Tuesday:
                    dt = dt.AddDays(1);
                    break;
                case System.DayOfWeek.Wednesday:
                    dt = dt.AddDays(2);
                    break;
                case System.DayOfWeek.Thursday:
                    dt = dt.AddDays(3);
                    break;
                case System.DayOfWeek.Friday:
                    dt = dt.AddDays(4);
                    break;
                case System.DayOfWeek.Saturday:
                    dt = dt.AddDays(5);
                    break;
                case System.DayOfWeek.Sunday:
                    dt = dt.AddDays(6);
                    break;
            }
            return dt.ToString("D");
        }