C#如何获取指定周的日期范围

1. 不允许跨年

1) 第一周的第一天从每年的第一天开始，最后一周的最后一天为每年的最后一天。

 1 static void Main(string[] args)
 2 {
 3     DateTime first, last;
 4     int[] years = new int[] { 2015, 2016, 2017, 2018 };
 5     int[] weeks = new int[] { 1, 52, 53 };
 6     foreach (int y in years)
 7     {
 8         foreach (int w in weeks)
 9         {
10             bool result = CalcWeekDay(y, w, out first, out last);
11             Console.WriteLine("{0}第{1}周（{2:yyyy-MM-dd} ~ {3:yyyy-MM-dd}） --{4}", y, w, first, last, result);
12         }
13         Console.WriteLine();
14     }
15 }
16
17 public static bool CalcWeekDay(int year, int week, out DateTime first, out DateTime last)
18 {
19     first = DateTime.MinValue;
20     last = DateTime.MinValue;
21     //年份超限
22     if (year < 1700 || year > 9999) return false;
23     //周数错误
24     if (week < 1 || week > 53) return false;
25     //指定年范围
26     DateTime start = new DateTime(year, 1, 1);
27     DateTime end = new DateTime(year, 12, 31);
28     int startWeekDay = (int)start.DayOfWeek;
29
30     if (week == 1)
31     {
32         first = start;
33         last = start.AddDays(6 - startWeekDay);
34     }
35     else
36     {
37         //周的起始日期
38         first = start.AddDays((7 - startWeekDay) + (week - 2) * 7);
39         last = first.AddDays(6);
40         if (last > end)
41         {
42             last = end;
43         }
44     }
45     return (first <= end);  

2) 程序执行结果

2. 允许跨年

1) 每年的尾周剩余天数计入下一年第一周。

 1 public static bool CalcWeekDay(int year, int week, out DateTime first, out DateTime last)
 2 {
 3     first = DateTime.MinValue;
 4     last = DateTime.MinValue;
 5     //年份超限
 6     if (year < 1700 || year > 9999) return false;
 7     //周数错误
 8     if (week < 1 || week > 53) return false;
 9     //指定年范围
10     DateTime start = new DateTime(year, 1, 1);
11     DateTime end = new DateTime(year, 12, 31);
12     int startWeekDay = (int)start.DayOfWeek;
13     //周的起始日期
14     first = start.AddDays((7 - startWeekDay) + (week - 2) * 7);
15     last = first.AddDays(6);
16     //结束日期跨年
17     return (last <= end);
18 }  

2) 程序执行结果