1 /// <summary>  
 2         /// 得到本周第一天(以星期一为第一天)  
 3         /// </summary>  
 4         /// <param name="datetime"></param>  
 5         /// <returns></returns>  
 6         public DateTime GetWeekFirstDayMon(DateTime datetime)
 7         {
 8             //星期一为第一天  
 9             int weeknow = Convert.ToInt32(datetime.DayOfWeek);
10 
11             //因为是以星期一为第一天，所以要判断weeknow等于0时，要向前推6天。  
12             weeknow = (weeknow == 0 ? (7 - 1) : (weeknow - 1));
13             int daydiff = (-1) * weeknow;
14 
15             //本周第一天  
16             string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
17             return Convert.ToDateTime(FirstDay);
18         }
19         /// <summary>  
20         /// 得到本周最后一天(以星期天为最后一天)  
21         /// </summary>  
22         /// <param name="datetime"></param>  
23         /// <returns></returns>  
24         public DateTime GetWeekLastDaySun(DateTime datetime)
25         {
26             //星期天为最后一天  
27             int weeknow = Convert.ToInt32(datetime.DayOfWeek);
28             weeknow = (weeknow == 0 ? 7 : weeknow);
29             int daydiff = (7 - weeknow);
30 
31             //本周最后一天  
32             string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
33             return Convert.ToDateTime(LastDay);
34         }