C#取两个时间的时间差并去除周末，取时间差的代码很多，但是能够只取工作日的时间差的代码很少

protected void Page_Load(object sender, EventArgs e)      {      DateTime start = Convert.ToDateTime("2012-12-10");          DateTime end= Convert.ToDateTime("2012-12-18");          TimeSpan span = end - start;          //int totleDay=span.Days;          //DateTime spanNu = DateTime.Now.Subtract(span);          int AllDays=Convert.ToInt32(span.TotalDays)+1;//差距的所有天数          int totleWeek = AllDays / 7;//差别多少周          int yuDay = AllDays % 7; //除了整个星期的天数          int lastDay = 0;          if (yuDay == 0) //正好整个周          {              lastDay = AllDays - (totleWeek * 2);          }          else          {                         int weekDay = 0;            int endWeekDay = 0;  //多余的天数有几天是周六或者周日            switch (start.DayOfWeek)            {                case DayOfWeek.Monday:                    weekDay = 1;                    break;                case DayOfWeek.Tuesday:                    weekDay = 2;                    break;                case DayOfWeek.Wednesday:                    weekDay = 3;                    break;                case DayOfWeek.Thursday:                    weekDay = 4;                    break;                case DayOfWeek.Friday:                    weekDay = 5;                    break;                case DayOfWeek.Saturday:                    weekDay = 6;                    break;                case DayOfWeek.Sunday:                    weekDay = 7;                    break;            }            if ((weekDay == 6 && yuDay >= 2) || (weekDay == 7 && yuDay >= 1) || (weekDay == 5 && yuDay >= 3) || (weekDay == 4 && yuDay >= 4) || (weekDay == 3 && yuDay >= 5) || (weekDay == 2 && yuDay >= 6) || (weekDay == 1 && yuDay >=7))            {                endWeekDay =2;            }            if ((weekDay == 6 && yuDay < 1) || (weekDay == 7 && yuDay <5) || (weekDay == 5 && yuDay < 2) || (weekDay == 4 && yuDay < 3) || (weekDay == 3 && yuDay < 4) || (weekDay == 2 && yuDay < 5) || (weekDay == 1 && yuDay < 6))          {                endWeekDay = 1;            }            lastDay = AllDays - (totleWeek * 2) - endWeekDay;          }          lblTime.Text = lastDay.ToString();      }