[英]Calculate the start and end date of a week given the week number and year in C# (based on the ISO specification)
[英]Calculate previous week's start and end date
在 C# 中计算前一周开始和结束日期的最佳方法是什么? 即今天 3 月 18 日将导致 3 月 9 日(上周星期一)和 3 月 15 日(上周星期日)。
我已经看到使用 DayOfWeek 和 switch 语句来计算偏移量,但想知道是否有更优雅的方法。
您可以跳过 while 循环并使用
DateTime mondayOfLastWeek = date.AddDays( -(int)date.DayOfWeek - 6 );
这假设您使用星期一作为一周的第一天。
DayOfWeek weekStart = DayOfWeek.Monday; // or Sunday, or whenever
DateTime startingDate = DateTime.Today;
while(startingDate.DayOfWeek != weekStart)
startingDate = startingDate.AddDays(-1);
DateTime previousWeekStart = startingDate.AddDays(-7);
DateTime previousWeekEnd = startingDate.AddDays(-1);
阅读:一次回溯一天,直到我们在本周开始,然后减去七到上周开始。
使用流利的日期时间 https://github.com/FluentDateTime/FluentDateTime
var dateTime = 1.Weeks().Ago();
var monday = dateTime.Previous(DayOfWeek.Sunday);
var sunday = dateTime.Next(DayOfWeek.Sunday);
当前接受的答案将通过给出本周的星期一而不是最后几周的星期一而在星期日失败。 (带有单元测试输出的代码)
DateTime mondayOfLastWeek = date.AddDays( -(int)date.DayOfWeek - 6 );
//Failed to get start of last-week from date-time: 2020-03-01T00:00:00.0000000Z
// Expected: 2020-02-17 00:00:00.000
// But was: 2020-02-24 00:00:00.000
以下代码解决了这个问题:
var dayOfWeek = (int) date.DayOfWeek - 1;
if (dayOfWeek < 0) dayOfWeek = 6;
var thisWeeksMonday = date.AddDays(-dayOfWeek).Date;
var lasWeeksMonday = thisWeeksMonday.AddDays(-7);
如果您愿意,可以将其简化为单行代码(我不建议使用这种几乎不可读的代码......):
var mondayOfLastWeek = date.AddDays(-(7 + ((int)date.DayOfWeek - 1 == -1 ? 6 : (int)date.DayOfWeek - 1)));
使用 DayOfWeek 将是实现此目的的一种方式:
DateTime date = DateTime.Now.AddDays(-7);
while (date.DayOfWeek != DayOfWeek.Monday)
{
date = date.AddDays(-1);
}
DateTime startDate = date;
DateTime endDate = date.AddDays(7);
您可以创建一个可以与 DayOfWeek 参数一起使用的 DateTime 扩展方法:
public static class DateTimeExtension
{
public static DateTime GetPreviousWeekDay(this DateTime currentDate, DayOfWeek dow)
{
int currentDay = (int)currentDate.DayOfWeek, gotoDay = (int)dow;
return currentDate.AddDays(-7).AddDays(gotoDay-currentDay);
}
}
然后按如下方式使用它:
DateTime testDate = new DateTime(2017, 01, 21);
Console.WriteLine(testDate.GetPreviousWeekDay(DayOfWeek.Sunday));
Console.WriteLine(testDate.GetPreviousWeekDay(DayOfWeek.Saturday));
要使用它从当前日期获取前一周(如问题中所述):
var prevWkStartDate = DateTime.Now.GetPreviousWeekDay(DayOfWeek.Monday);
var prevWkEndDate = DateTime.Now.GetPreviousWeekDay(DayOfWeek.Sunday);
Console.Write($"Previous week starts at {prevWkStartDate.ToShortDateString()}");
Console.WriteLine($" and ends at {prevWkEndDate.ToShortDateString()}");
更新:似乎这需要修复(示例日期:2020 年 12 月 10 日):
public static DateTime GetPreviousWeekDay(this DateTime currentDate, DayOfWeek dow)
{
int d = 0; if (dow == DayOfWeek.Sunday) { dow = DayOfWeek.Saturday; d = 1; }
int currentDay = (int)currentDate.DayOfWeek, gotoDay = (int)dow;
return currentDate.AddDays(-7).AddDays(gotoDay - currentDay + d);
}
公认的解决方案实际上是不正确的。
您必须在一周“休息”时进行切换,即当它认为一周结束或开始时,并且接受的解决方案中的公式没有。
这在星期一不像一周开始那么明显,但如果您将星期四视为本周末,则更是如此。
正确的公式是(以星期四为结束日):
DateTime thu = date.AddDays(-(int)(date.AddDays(-5).DayOfWeek) -1);
对于星期一,-5 将切换到 -2。
打印输出示例代码
String s = "";
DateTime date = new DateTime(2017, 1, 1);
for (int i = 0; i < 14; i++)
{
date = date.AddDays(1);
DateTime thu = date.AddDays(-(int)(date.AddDays(-5).DayOfWeek) -1);
DateTime mon = date.AddDays(-(int)(date.AddDays(-2).DayOfWeek) -1);
s += date.ToString() + " - Thu: " + thu.ToString() + " - Mon: " + mon.ToString() + "\r\n";
}
Console.WriteLine(s);
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