有時(shí)，在我們的程序中需要判斷某個(gè)日期是一年中的第幾周，以便進(jìn)行相關(guān)的處理，下面這個(gè)函數(shù)就是用來判斷某個(gè)日期是第一年中的第幾周。

        ///   <summary>   
        ///   取指定日期是一年中的第幾周   
        ///   </summary>   
        ///   <param   name="dateTime">給定的日期</param>   
        ///   <returns>返回 該日期所在一年中的周數(shù)</returns>   
        public static int WeekOfYear(DateTime dateTime)
        {
            int firstdayofweek = System.Convert.ToDateTime(dateTime.Year.ToString() + "- " + "1-1 ").DayOfWeek.GetHashCode();
            int days = dateTime.DayOfYear;
            int daysOutOneWeek = days - (7 - firstdayofweek);
            if (daysOutOneWeek <= 0)
            {
                return 1;
            }
            else
            {
                int weeks = daysOutOneWeek / 7;
                if (daysOutOneWeek % 7 != 0)
                {
                    weeks++;
                }
                return weeks + 1;
            }
        }