我尝试了几次，但我没有解决从星期一开始的一周的问题，导致我的下一个星期一是星期天。所以我对它做了一些修改，让它与下面的代码一起工作:

int delta = DayOfWeek.Monday - DateTime.Now.DayOfWeek;
DateTime monday = DateTime.Now.AddDays(delta == 1 ? -6 : delta);
return monday;

在c#中试试这个。使用这段代码，您可以获得给定一周的第一个日期和最后一个日期。在这里，周日是第一天，周六是最后一天，但您可以根据您的文化设置这两天。

DateTime firstDate = GetFirstDateOfWeek(DateTime.Parse("05/09/2012").Date, DayOfWeek.Sunday);
DateTime lastDate = GetLastDateOfWeek(DateTime.Parse("05/09/2012").Date, DayOfWeek.Saturday);

public static DateTime GetFirstDateOfWeek(DateTime dayInWeek, DayOfWeek firstDay)
{
    DateTime firstDayInWeek = dayInWeek.Date;
    while (firstDayInWeek.DayOfWeek != firstDay)
        firstDayInWeek = firstDayInWeek.AddDays(-1);

    return firstDayInWeek;
}

public static DateTime GetLastDateOfWeek(DateTime dayInWeek, DayOfWeek firstDay)
{
    DateTime lastDayInWeek = dayInWeek.Date;
    while (lastDayInWeek.DayOfWeek != firstDay)
        lastDayInWeek = lastDayInWeek.AddDays(1);

    return lastDayInWeek;
}

这将给你前一个星期天(我想):

DateTime t = DateTime.Now;
t -= new TimeSpan ((int) t.DayOfWeek, 0, 0, 0);

周末也一样(以Compile This's answer的方式):

    public static DateTime EndOfWeek(this DateTime dt)
    {
        int diff = 7 - (int)dt.DayOfWeek;

        diff = diff == 7 ? 0 : diff;

        DateTime eow = dt.AddDays(diff).Date;

        return new DateTime(eow.Year, eow.Month, eow.Day, 23, 59, 59, 999) { };
    }

我尝试了几次，但我没有解决从星期一开始的一周的问题，导致我的下一个星期一是星期天。所以我对它做了一些修改，让它与下面的代码一起工作:

int delta = DayOfWeek.Monday - DateTime.Now.DayOfWeek;
DateTime monday = DateTime.Now.AddDays(delta == 1 ? -6 : delta);
return monday;

我是这样做的:

DateTime.Now.Date.AddDays(-(DateTime.Now.Date.DayOfWeek == 0 ? 7 : (int)DateTime.Now.Date.DayOfWeek) + 1)

这段代码所做的就是从给定的日期时间中减去天数。

如果星期几是0(星期日)，那么减去7，否则减去星期几。

然后在前一行的结果上加上1天，这将给出该日期的星期一。

这样你就可以在最后摆弄数字(1)来得到你想要的那一天。

private static DateTime GetDay(DateTime date, int daysAmount = 1)
{
    return date.Date.AddDays(-(date.Date.DayOfWeek == 0 ? 7 : (int)date.Date.DayOfWeek) + daysAmount);
}

如果你真的想使用DayOfWeek枚举，那么可以使用这样的东西…虽然我个人更喜欢上面的那个，因为我可以增加或减少任何数量的天数。

private static DateTime GetDayOfWeek(DateTime date, DayOfWeek dayOfWeek = DayOfWeek.Monday)
{
    return date.Date.AddDays(-(date.Date.DayOfWeek == 0 ? 7 : (int)date.Date.DayOfWeek) + (dayOfWeek == 0 ? 7 : (int)dayOfWeek));
}