C#獲取指定日期為一年中的第幾周

/// <summary>
/// 獲取指定日期，在為一年中為第幾周
/// </summary>
/// <param name="dt">指定時間</param>
/// <reutrn>返回第幾周</reutrn>
private static int GetWeekOfYear(DateTime dt)
{
GregorianCalendar gc = new GregorianCalendar();
int weekOfYear = gc.GetWeekOfYear(dt,CalendarWeekRule.FirstDay, DayOfWeek.Monday);
return weekOfYear;
}