根据传入的时间得到传入时间天在这一年的周数函数

private int DatePart(System.DateTime dt)
  {
   
   int weeknow = Convert.ToInt32(dt.DayOfWeek);
   int daydiff = (-1) * (weeknow+1);
   int days = System.DateTime.Now.AddDays(daydiff).DayOfYear;
   int weeks = days/7;
   if(days%7 != 0)
   {
    weeks++;
   }
   return (weeks+1);
  }