C#时间函数扩展（计算第几周和周起止日期）

 

//本周是本年第几周


private int DatePart(System.DateTime dt)
{
   int weeknow = Convert.ToInt32(dt.DayOfWeek);//今天星期几
   int daydiff = (-1) * (weeknow+1);//今日与上周末的天数差
   int days = System.DateTime.Now.AddDays(daydiff).DayOfYear;//上周末是本年第几天
   int weeks = days/7;
   if(days%7 != 0)
{
    weeks++;
   }
   //此时，weeks为上周是本年的第几周
   return (weeks+1);
  }

 
//本周起止日期

 private string WeekRange(System.DateTime dt)
{
   int weeknow = Convert.ToInt32(dt.DayOfWeek);
   int daydiff = (-1) * weeknow;
   int dayadd = 6-weeknow;
   string dateBegin = System.DateTime.Now.AddDays(daydiff).Date.ToString("MM月dd日");
   string dateEnd = System.DateTime.Now.AddDays(dayadd).Date.ToString("MM月dd日");
   return dateBegin + " - " +dateEnd;
  }

//计算第几周（重新修改后）
public int GetWeekOfCurrDate(DateTime dt)
        {
            int Week = 1;
            int nYear = dt.Year;
            System.DateTime FirstDayInYear = new DateTime(nYear, 1, 1);
            System.DateTime LastDayInYear = new DateTime(nYear, 12, 31);
            int DaysOfYear = Convert.ToInt32(LastDayInYear.DayOfYear);
            int WeekNow = Convert.ToInt32(FirstDayInYear.DayOfWeek) - 1;
            if (WeekNow < 0) WeekNow = 6;
            int DayAdd = 6 - WeekNow;
            System.DateTime BeginDayOfWeek = new DateTime(nYear, 1, 1);
            System.DateTime EndDayOfWeek = BeginDayOfWeek.AddDays(DayAdd);
            Week = 2;
            for (int i = DayAdd + 1; i <= DaysOfYear; i++)
            {
                BeginDayOfWeek = FirstDayInYear.AddDays(i);
                if (i + 6 > DaysOfYear)
                {
                    EndDayOfWeek = BeginDayOfWeek.AddDays(DaysOfYear - i - 1);
                }
                else
                {
                    EndDayOfWeek = BeginDayOfWeek.AddDays(6);
                }

                if (dt.Month == EndDayOfWeek.Month && dt.Day <= EndDayOfWeek.Day)
                {
                    break;
                }
                Week++;
                i = i + 6;
            }
            return Week;
        }