如该MSDN页面中所述，ISO8601周和.Net周编号之间存在细微差异。
您可以在MSDN博客中参考本文以获得更好的解释：“ Microsoft .Net中的ISO
8601年度格式 ”
简而言之，.Net允许将数年的时间分成数年，而ISO标准则不允许。在文章中，还有一个简单的函数可以为一年的最后一周获取正确的ISO 8601周编号。
更新 以下方法实际上返回1，
2012-12-31在ISO 8601中该值是正确的（例如德国）。
// This presumes that weeks start with Monday.// Week 1 is the 1st week of the year with a Thursday in it.public static int GetIso8601WeekOfYear(DateTime time){ // Seriously cheat. If its Monday, Tuesday or Wednesday, then it'll // be the same week# as whatever Thursday, Friday or Saturday are, // and we always get those right DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time); if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday) { time = time.AddDays(3); } // Return the week of our adjusted day return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);}
