C#时间函数扩展

//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;
  }

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