获取某年中第几个礼拜的第一天的函数

今天有朋友问题我如何获取某年中第几个礼拜的时间范围，似乎以前好像记得.NET有，不过今天一查没有翻到，在google搜索到这个，希望以后能自己用上，测试已经通过。

        public static void Main()
        {

            DateTime date1 = GoToWeek(2012, 2);
            Console.Write(date1.ToString());
            Console.Read();
        }

        private static DateTime GoToWeek(int year, int week)
        {
            // use the current culture
            System.Globalization.CultureInfo ci = System.Threading.Thread.CurrentThread.CurrentCulture;

            // get first day of week from culture
            DayOfWeek fdow = ci.DateTimeFormat.FirstDayOfWeek;

            // new empty Date (so starts 01/01/0001)
            DateTime d = new DateTime();

            // year starts at 1, so take away 1 from desired year to prevent going to the next one
            d = d.AddYears(year - 1);

            // get day January 1st falls on
            int startDay = (int)d.DayOfWeek;

            // get the difference between the first day of the week, and the day January 1st starts on
            int difference = (int)fdow - startDay;
            // if it is positive (i.e. after first day of week), take away 7
            if (difference > 0)
            {
                difference = difference - 7;
            }

            // already on week 1, so add desired number of weeks - 1 * days in week
            if (week > 1)
            {
                d = d.AddDays((week - 1) * 7 + difference);
            }

            return d;
        }

        private static int WeekOfYear(DateTime date)
        {
            // use the current culture
            System.Globalization.CultureInfo ci = System.Threading.Thread.CurrentThread.CurrentCulture;
            // use current culture's calendar
            System.Globalization.Calendar cal = ci.Calendar;
            // get the calendar week rule (i.e. what determines the first week in the year)
            System.Globalization.CalendarWeekRule cwr = ci.DateTimeFormat.CalendarWeekRule;
            // get the first day of week for the current culture
            DayOfWeek fdow = ci.DateTimeFormat.FirstDayOfWeek;
            // return the week
            return cal.GetWeekOfYear(date, cwr, fdow);
        }