.Net 使用 GregorianCalendar 获取任意一天为一年的第几周

private static int GetWeekOfYear(DateTime dt)
{
    GregorianCalendar gc = new GregorianCalendar();
    int weekOfYear = gc.GetWeekOfYear(dt, CalendarWeekRule.FirstDay/*设置第一天*/, DayOfWeek.Monday/*设置周一为一周的第一天*/);
    return weekOfYear;
}