关键代码：

        /// <summary>        /// 获取日期是一年中第几个星期        /// </summary>        /// <param name="date">需要计算的时间</param>        /// <returns>一年中第几个星期</returns>        public static int GetWeekNumber(this DateTime date)        {            var _cultureInfo = CultureInfo.CurrentCulture;            return _cultureInfo.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);        }

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