使用Fluent DateTime:

var monday = DateTime.Now.Previous(DayOfWeek.Monday);
var sunday = DateTime.Now.Previous(DayOfWeek.Sunday);

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;
}

以下是一些答案的组合。它使用一个扩展方法，允许传入区域性。如果没有传入，则使用当前区域性。这将为它提供最大的灵活性和重用性。

/// <summary>
/// Gets the date of the first day of the week for the date.
/// </summary>
/// <param name="date">The date to be used</param>
/// <param name="cultureInfo">If none is provided, the current culture is used</param>
/// <returns>The date of the beggining of the week based on the culture specifed</returns>
public static DateTime StartOfWeek(this DateTime date, CultureInfo cultureInfo=null) =>
    date.AddDays(-1 * (7 + (date.DayOfWeek - (cultureInfo ?? CultureInfo.CurrentCulture).DateTimeFormat.FirstDayOfWeek)) % 7).Date;

使用示例:

public static void TestFirstDayOfWeekExtension() {
    DateTime date = DateTime.Now;
    foreach(System.Globalization.CultureInfo culture in CultureInfo.GetCultures(CultureTypes.UserCustomCulture | CultureTypes.SpecificCultures)) {
        Console.WriteLine($"{culture.EnglishName}: {date.ToShortDateString()} First Day of week: {date.StartOfWeek(culture).ToShortDateString()}");
    }
}

使用扩展方法:

public static class DateTimeExtensions
{
    public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
    {
        int diff = (7 + (dt.DayOfWeek - startOfWeek)) % 7;
        return dt.AddDays(-1 * diff).Date;
    }
}

可以这样使用:

DateTime dt = DateTime.Now.StartOfWeek(DayOfWeek.Monday);
DateTime dt = DateTime.Now.StartOfWeek(DayOfWeek.Sunday);

这将返回一周的开始和结束日期:

    private string[] GetWeekRange(DateTime dateToCheck)
    {
        string[] result = new string[2];
        TimeSpan duration = new TimeSpan(0, 0, 0, 0); //One day 
        DateTime dateRangeBegin = dateToCheck;
        DateTime dateRangeEnd = DateTime.Today.Add(duration);

        dateRangeBegin = dateToCheck.AddDays(-(int)dateToCheck.DayOfWeek);
        dateRangeEnd = dateToCheck.AddDays(6 - (int)dateToCheck.DayOfWeek);

        result[0] = dateRangeBegin.Date.ToString();
        result[1] = dateRangeEnd.Date.ToString();
        return result;

    }

我已经在我的博客上发布了计算周、月、季度和年的开始/结束的完整代码 ZamirsBlog

通过这种方式计算，您可以选择一周中的哪一天表示新一周的开始(在示例中，我选择了星期一)。

请注意，对星期一进行这个计算将得到当前的星期一，而不是以前的星期一。

//Replace with whatever input date you want
DateTime inputDate = DateTime.Now;

//For this example, weeks start on Monday
int startOfWeek = (int)DayOfWeek.Monday;

//Calculate the number of days it has been since the start of the week
int daysSinceStartOfWeek = ((int)inputDate.DayOfWeek + 7 - startOfWeek) % 7;

DateTime previousStartOfWeek = inputDate.AddDays(-daysSinceStartOfWeek);