c# 获取某日期所在周的第一天和最后一天

转自：http://blog.csdn.net/joyhen/article/details/9179763[csharp] view plain copy

1. using System;  
2. using System.Collections.Generic;  
3. using System.Linq;  
4. using System.Text;  
5.   
6. namespace WyfClass  
7. {  
8. public class tools  
9. {  
10. /// <summary>  
11. /// 得到本周第一天(以星期天为第一天)  
12. /// </summary>  
13. /// <param name="datetime"></param>  
14. /// <returns></returns>  
15. public DateTime GetWeekFirstDaySun(DateTime datetime)  
16. {  
17.     //星期天为第一天  
18.     int weeknow = Convert.ToInt32(datetime.DayOfWeek);  
19.     int daydiff = (-1) * weeknow;  
20.   
21.     //本周第一天  
22.     string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");  
23.     return Convert.ToDateTime(FirstDay);  
24. }  
25.   
26. /// <summary>  
27. /// 得到本周第一天(以星期一为第一天)  
28. /// </summary>  
29. /// <param name="datetime"></param>  
30. /// <returns></returns>  
31. public DateTime GetWeekFirstDayMon(DateTime datetime)  
32. {  
33.     //星期一为第一天  
34.     int weeknow = Convert.ToInt32(datetime.DayOfWeek);  
35.   
36.     //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。  
37.     weeknow = (weeknow == 0 ? (7 - 1) : (weeknow - 1));  
38.     int daydiff = (-1) * weeknow;  
39.   
40.     //本周第一天  
41.     string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");  
42.     return Convert.ToDateTime(FirstDay);  
43. }  
44.   
45. /// <summary>  
46. /// 得到本周最后一天(以星期六为最后一天)  
47. /// </summary>  
48. /// <param name="datetime"></param>  
49. /// <returns></returns>  
50. public DateTime GetWeekLastDaySat(DateTime datetime)  
51. {  
52.     //星期六为最后一天  
53.     int weeknow = Convert.ToInt32(datetime.DayOfWeek);  
54.     int daydiff = (7 - weeknow) - 1;  
55.   
56.     //本周最后一天  
57.     string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");  
58.     return Convert.ToDateTime(LastDay);  
59. }  
60.   
61. /// <summary>  
62. /// 得到本周最后一天(以星期天为最后一天)  
63. /// </summary>  
64. /// <param name="datetime"></param>  
65. /// <returns></returns>  
66. public DateTime GetWeekLastDaySun(DateTime datetime)  
67. {  
68.     //星期天为最后一天  
69.     int weeknow = Convert.ToInt32(datetime.DayOfWeek);  
70.     weeknow = (weeknow == 0 ? 7 : weeknow);  
71.     int daydiff = (7 - weeknow);  
72.   
73.     //本周最后一天  
74.     string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");  
75.     return Convert.ToDateTime(LastDay);  
76. }  
77. }  
78. }