11

我需要知道周数的一周的第一天和最后一天的日期。

我得到一个开始日期和一个结束日期，代表给定年份中选定周的第一天和最后一天。那么我需要获取上一年同一周的开始日期和结束日期，对一些数据进行图形比较。

我设法根据给定的开始日期和结束日期获得周数。现在我需要获取上一年同一周的第一天和最后一天的日期。我怎么能最快地做到这一点？

编辑：这就是我得到周数的方式：

 private int GetWeekNumber(DateTime date)
    {
        GregorianCalendar calendar = new GregorianCalendar(GregorianCalendarTypes.USEnglish);
        return calendar.GetWeekOfYear(date, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);            
    }
4

8 回答 8

25

您可以使用以下两种方法根据给定年份计算给定周数的周数和开始日期：

// this method is borrowed from http://stackoverflow.com/a/11155102/284240
public static int GetIso8601WeekOfYear(DateTime time)
{
    DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
    if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
    {
        time = time.AddDays(3);
    }

    return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
} 

public static DateTime FirstDateOfWeek(int year, int weekOfYear, System.Globalization.CultureInfo ci)
{
    DateTime jan1 = new DateTime(year, 1, 1);
    int daysOffset = (int)ci.DateTimeFormat.FirstDayOfWeek - (int)jan1.DayOfWeek;
    DateTime firstWeekDay = jan1.AddDays(daysOffset);
    int firstWeek = ci.Calendar.GetWeekOfYear(jan1, ci.DateTimeFormat.CalendarWeekRule, ci.DateTimeFormat.FirstDayOfWeek);
    if ((firstWeek <= 1 || firstWeek >= 52) && daysOffset >= -3)
    {
        weekOfYear -= 1;
    }
    return firstWeekDay.AddDays(weekOfYear * 7);
}

然后您可以通过以下方式获取两个日期：

// 46
int thisWeekNumber = GetIso8601WeekOfYear(DateTime.Today); 
// 11/11/2013  
DateTime firstDayOfWeek= FirstDateOfWeek(2013, thisWeekNumber, CultureInfo.CurrentCulture); 
// 11/12/2012  
DateTime firstDayOfLastYearWeek = FirstDateOfWeek(2012, thisWeekNumber, CultureInfo.CurrentCulture);

增加 6 天以结束一周。

于 2013-11-11T08:29:14.507 回答
20

这是我的解决方案：

public static DateTime FirstDayOfWeek(DateTime date)
{
    DayOfWeek fdow = CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;
    int offset = fdow - date.DayOfWeek;
    DateTime fdowDate = date.AddDays(offset);
    return fdowDate;
}

public static DateTime LastDayOfWeek(DateTime date)
{
    DateTime ldowDate = FirstDayOfWeek(date).AddDays(6);
    return ldowDate;
}
于 2014-11-25T10:32:27.977 回答
2

上述方法计算出 2016 年第一周的第一个日期错误。

基于先前答案的固定代码

 public DateTime FirstDateOfWeek(
        int year,
        int weekOfYear)
    {
        var newYear = new DateTime(year, 1, 1);
        var weekNumber = newYear.GetIso8601WeekOfYear(); 

        DateTime firstWeekDate;

        if (weekNumber != 1)
        {
            var dayNumber = (int) newYear.DayOfWeek;
            firstWeekDate = newYear.AddDays(7 - dayNumber + 1);
        }
        else
        {
            var dayNumber = (int)newYear.DayOfWeek;
            firstWeekDate = newYear.AddDays(-dayNumber + 1);
        }

        if (weekOfYear == 1)
        {
            return firstWeekDate;
        }

        return firstWeekDate.AddDays(7 * (weekOfYear - 1));
    }

加试

    [TestCase(2016, 1, 2016, 1, 4)]
    [TestCase(2016, 2, 2016, 1, 11)]
    [TestCase(2016, 52, 2016, 12, 26)]
    [TestCase(2014, 1, 2013, 12, 30)]
    public void FirstDateOfWeek_ShouldReturnCorrectDay(int year, int weekNumber, int correctYear, int correctMonth, int correctDay)
    {
        var helper = new DateHelper();
        var result = helper.FirstDateOfWeek(year, weekNumber);

        Assert.That(result.Year, Is.EqualTo(correctYear));
        Assert.That(result.Month, Is.EqualTo(correctMonth));
        Assert.That(result.Day, Is.EqualTo(correctDay));
    }
于 2016-01-11T17:12:10.347 回答
1 
    private static DateTime FirstDateOfWeek(int year, int weekOfYear)
    {
        var firstDate = new DateTime(year, 1, 4);
        //first thursday of the week defines the first week (https://en.wikipedia.org/wiki/ISO_8601)
        //Wiki: the 4th of january is always in the first week
        while (firstDate.DayOfWeek != DayOfWeek.Monday)
            firstDate = firstDate.AddDays(-1);

        return firstDate.AddDays((weekOfYear - 1)*7);
    }

更简单、更高效的解决方案！

于 2016-06-06T14:12:52.090 回答
0

从您的原始 DateTime 中减去 1 年，然后再次调用您的 GetWeekNumber 方法。

TimeSpan oneYear = dateTime.AddYears(1) - dateTime;
var lastYearWeekNumber = GetWeekNumber(dateTime.Subtract(oneYear));
于 2013-11-11T08:31:55.590 回答
0

您可以根据传递的参数日期找到如何获取当前或上周的第一个和最后一个日期的解决方案，现在您还可以获取上一年同一周的第一天和最后一天的日期。

您还可以更改一些设置以更改您的第一个工作日以获得您需要的结果。

假设您的工作日从星期一开始，星期日除外，那么您需要做的就是改变开关盒并继续获得您想要的结果。

public DateTime GetFirstDateOfCurrentWeek(DateTime dtDate)
{
 //In this function we assumed that week start from sunday and end on saturday
    int no = 0;
    switch (dtDate.DayOfWeek.ToString())
    {
        case "Sunday":
            no = 0;
            break;
        case "Monday":
            no = 1;
            break;
        case "Tuesday":
            no = 2;
            break;
        case "Wednesday":
            no = 3;
            break;
        case "Thursday":
            no = 4;
            break;
        case "Friday":
            no = 5;
            break;
        case "Saturday":
            no = 6;
            break;
        default:
            no = 0;
            break;
    }
    return dtDate.AddDays(-no);
 }

public DateTime GetLastDateOfCurrentWeek(DateTime dtDate)
{
    int no = 0;
    switch (dtDate.DayOfWeek.ToString())
    {
        case "Saturday":
            no = 0;
            break;
        case "Friday":
            no = 1;
            break;
        case "Thursday":
            no = 2;
            break;
        case "Wednesday":
            no = 3;
            break;
        case "Tuesday":
            no = 4;
            break;
        case "Monday":
            no = 5;
            break;
        case "Sunday":
            no = 6;
            break;
        default:
            no = 0;
            break;
    }
    return dtDate.AddDays(no);
}

public DateTime GetFirstDateOfLastWeek(DateTime dtDate)
{
    return GetFirstDateOfCurrentWeek(dtDate).AddDays(-7);
}

public DateTime GetLastDateOfLastWeek(DateTime dtDate)
{
    return GetLastDateOfCurrentWeek(dtDate).AddDays(-7);
}

public DateTime GetFirstDateOfCurrentWeekOfPrvYear(DateTime dtDate)
{
    int dayOfYear = dtDate.DayOfYear;
    DateTime firstDateOfThisYear = (Convert.ToDateTime("01/01/" + dtDate.Year.ToString()));
    DateTime firstDateofPrvYear = (firstDateOfThisYear.AddYears(-1));
    DateTime dateOfPrvYear = (firstDateofPrvYear.AddDays(dayOfYear));

    return GetFirstDateOfCurrentWeek(dateOfPrvYear);
}

public DateTime GetLastDateOfCurrentWeekOfPrvYear(DateTime dtDate)
{
    int dayOfYear = dtDate.DayOfYear;
    DateTime firstDateOfThisYear = Convert.ToDateTime("01/01/" + dtDate.Year.ToString());
    DateTime firstDateofPrvYear = (firstDateOfThisYear.AddYears(-1));
    DateTime dateOfPrvYear = (firstDateofPrvYear.AddDays(dayOfYear));

    return GetLastDateOfCurrentWeek(dateOfPrvYear);
}

DateTime dt = Convert.ToDateTime("12/12/2019");

int dayOfYear = dt.DayOfYear;
string weekOfYear = (dt.DayOfYear / 7).ToString();
string firstDateOfThisYear = (Convert.ToDateTime("01/01/" + dt.Year.ToString())).ToShortDateString();
string firstDateofPrvYear = (Convert.ToDateTime(firstDateOfThisYear).AddYears(-1)).ToShortDateString();
string dateOfPrvYear = (Convert.ToDateTime(firstDateofPrvYear).AddDays(dayOfYear)).ToShortDateString();
string firstDateofWeekPrvYear = GetFirstDateOfCurrentWeek(Convert.ToDateTime(dateOfPrvYear)).ToShortDateString();
string lastDateofWeekPrvYear = GetLastDateOfCurrentWeek(Convert.ToDateTime(dateOfPrvYear)).ToShortDateString();
string weekOfPrvYear = (Convert.ToDateTime(dateOfPrvYear).DayOfYear / 7).ToString();

MessageBox.Show("Day of Year: " + dayOfYear.ToString());
MessageBox.Show("Week of Year: " + weekOfYear);
MessageBox.Show("First day of this year: " + firstDateOfThisYear);
MessageBox.Show("First day of prv year: " + firstDateofPrvYear);
MessageBox.Show("Date of Prv Year: " + dateOfPrvYear);
MessageBox.Show("First Date of Week Prv Year: " + firstDateofWeekPrvYear);
MessageBox.Show("Last Date of Week Prv Year: " + lastDateofWeekPrvYear);
MessageBox.Show("Day of Prv Year: " + weekOfPrvYear.ToString());
于 2020-12-02T10:00:26.733 回答
-1

由于每周有 7 天，您将知道第 10 周与第 71 - 77 天相同。您知道每月的天数（不要忘记闰年）。构建确切的日期，然后，您可以获得有关这些日子的信息。

于 2013-11-11T08:20:40.367 回答
-1

Tim Schmelter 的方法不适用于每周从星期一开始的瑞典 (sv-SE) 文化。这已经通过 en-US 和 sv-SE 进行了测试。

    public static DateTime GetFirstDateOfWeek(int year, int weekOfYear, CultureInfo cultureInfo)
    {
        DateTime jan1 = new DateTime(year, 1, 1);
        int daysOffset = (int)cultureInfo.DateTimeFormat.FirstDayOfWeek - (int)jan1.DayOfWeek;
        DateTime firstWeekDay = jan1.AddDays(daysOffset);
        int firstWeek = cultureInfo.Calendar.GetWeekOfYear(jan1, cultureInfo.DateTimeFormat.CalendarWeekRule, cultureInfo.DateTimeFormat.FirstDayOfWeek);
        if (firstWeek == 1)
        {
            weekOfYear -= 1;
        }
        return firstWeekDay.AddDays(weekOfYear * 7);
    }
于 2016-02-10T15:02:22.393 回答