System.Globalization.Calendar.AddWeeks C# (CSharp) Method

        public virtual DateTime AddWeeks(DateTime time, int weeks) {
            return (AddDays(time, weeks * 7));
        }

        /// <summary>
        /// 根据一年中的第几周获取该周的开始日期与结束日期
        /// </summary>
        /// <param name="year"></param>
        /// <param name="weekNumber"></param>
        /// <param name="culture"></param>
        /// <returns></returns>
        public static Tuple <DateTime, DateTime> GetFirstEndDayOfWeek(int year, int weekNumber, System.Globalization.CultureInfo culture)
        {
            System.Globalization.Calendar calendar = culture.Calendar;
            DateTime  firstOfYear    = new DateTime(year, 1, 1, calendar);
            DateTime  targetDay      = calendar.AddWeeks(firstOfYear, weekNumber - 1);
            DayOfWeek firstDayOfWeek = culture.DateTimeFormat.FirstDayOfWeek;

            while (targetDay.DayOfWeek != firstDayOfWeek)
            {
                targetDay = targetDay.AddDays(-1);
            }

            return(Tuple.Create <DateTime, DateTime>(targetDay, targetDay.AddDays(6)));
        }