1 using System;
2
3 namespace ConsoleAppDemo
4 {
5 class Program
6 {
7 static void Main(string[] args)
8 {
9 DateTime now = DateTime.Now;
10 Console.WriteLine($"First Day Of Month：{now.FirstDayOfMonth()}");
11 Console.WriteLine($"Last Day Of Month：{now.LastDayOfMonth()}");
12 Console.WriteLine($"First Day Of Previous Month：{now.FirstDayOfPreviousMonth()}");
13 Console.WriteLine($"Last Day Of Previous Month：{now.LastDayOfPreviousMonth()}");
14 Console.WriteLine($"First Day Of Previous Week：{now.FirstDayOfPreviousWeek()}");
15 Console.WriteLine($"Last Day Of Previous Week：{now.LastDayOfPreviousWeek()}");
16 Console.ReadKey();
17 }
18 }
19
20 public static class DateTimeExtension
21 {
22 /// 取得某月的第一天
23 /// </summary>
24 /// <param name="datetime">要取得月份第一天的时间</param>
25 /// <returns></returns>
26 public static DateTime FirstDayOfMonth(this DateTime datetime)
27 {
28 return datetime.AddDays(1 - datetime.Day);
29 }
30 /// <summary>
31 /// 取得某月的最后一天
32 /// </summary>
33 /// <param name="datetime">要取得月份最后一天的时间</param>
34 /// <returns></returns>
35 public static DateTime LastDayOfMonth(this DateTime datetime)
36 {
37 return FirstDayOfMonth(datetime).AddMonths(1).AddDays(-1);
38 }
39
40 /// <summary>
41 /// 取得上个月第一天
42 /// </summary>
43 /// <param name="datetime">要取得上个月第一天的当前时间</param>
44 /// <returns></returns>
45 public static DateTime FirstDayOfPreviousMonth(this DateTime datetime)
46 {
47 return FirstDayOfMonth(datetime).AddMonths(-1);
48 }
49
50 /// <summary>
51 /// 取得上个月的最后一天
52 /// </summary>
53 /// <param name="datetime">要取得上个月最后一天的当前时间</param>
54 /// <returns></returns>
55 public static DateTime LastDayOfPreviousMonth(this DateTime datetime)
56 {
57 return FirstDayOfMonth(datetime).AddDays(-1);
58 }
59
60 /// <summary>
61 /// 取得上周的第一天
62 /// </summary>
63 /// <param name="datetime">要取得上周第一天的当前时间</param>
64 /// <returns></returns>
65 public static DateTime FirstDayOfPreviousWeek(this DateTime datetime)
66 {
67 return LastDayOfPreviousWeek(datetime).AddDays(-6);
68 }
69
70 /// <summary>
71 /// 取得上周的最后一天
72 /// </summary>
73 /// <param name="datetime">要取得上周最后一天的当前时间</param>
74 /// <returns></returns>
75 public static DateTime LastDayOfPreviousWeek(this DateTime datetime)
76 {
77 int dayOfWeek = (int)datetime.DayOfWeek;
78 return datetime.AddDays(dayOfWeek == 0 ? -7 : -dayOfWeek);
79 }
80 }
81
82 }
