获取当前日期是一年中的第几周

   /// <summary>
        /// 获取当前日期是一年中的第几周
        /// </summary>
        /// <param name="time"></param>
        /// <returns></returns>
        public static int CurrentWeekIndex(this DateTime time)
        {
            var calendar = CultureInfo.CurrentCulture.Calendar;
            return calendar.GetWeekOfYear(time, CalendarWeekRule.FirstDay, DayOfWeek.Monday);
        }