C#获取指定日期为一年中的第几周

/// 

/// 获取指定日期，在为一年中为第几周
/// 
/// 指定时间
/// 返回第几周
private static int GetWeekOfYear(DateTime dt)
{
GregorianCalendar gc = new GregorianCalendar();
int weekOfYear = gc.GetWeekOfYear(dt,CalendarWeekRule.FirstDay, DayOfWeek.Monday);
return weekOfYear;
}