如何：从特定日期中提取星期几

项目
05/09/2023

利用 .NET，可以很容易地确定某个特定日期是星期几，以及显示某个特定日期的本地化星期几名称。指示与特定日期相对应的星期几的枚举值可以从 DayOfWeek 或 DayOfWeek 属性中获取。与此不同的是，检索星期几名称是一项格式化操作，可通过调用格式化方法来执行，例如日期和时间值的 ToString 方法或 String.Format 方法。本文演示如何执行这些格式化操作。

提取指示星期几的数字

使用静态 DateTime.Parse 或 DateTimeOffset.Parse 方法将日期的字符串表示形式转换为 DateTime 或 DateTimeOffset 值。
使用 DateTime.DayOfWeek 或 DateTimeOffset.DayOfWeek 属性检索指示星期几的 DayOfWeek 值。
如有必要，可将 DayOfWeek 值强制转换（在 C# 中）或转换（在 Visual Basic 中）为整数。

下面的示例将显示一个整数，用于表示特定日期的星期几：

using System;

public class Example
{
   public static void Main()
   {
      DateTime dateValue = new DateTime(2008, 6, 11);
      Console.WriteLine((int) dateValue.DayOfWeek);
   }
}
// The example displays the following output:
//       3

Module Example
    Public Sub Main()
        Dim dateValue As Date = #6/11/2008#
        Console.WriteLine(dateValue.DayOfWeek)
    End Sub
End Module
' The example displays the following output:
'    3

提取缩写的工作日名称

使用静态 DateTime.Parse 或 DateTimeOffset.Parse 方法将日期的字符串表示形式转换为 DateTime 或 DateTimeOffset 值。

你可以提取当前区域性或特定区域性的缩写的星期几名称：

若要提取当前区域性的缩写的星期几名称，请调用日期和时间值的 DateTime.ToString(String) 或 DateTimeOffset.ToString(String) 实例方法，并以 format 参数的形式传递字符串 ddd。下面的示例演示 ToString(String) 方法的调用：

using System;

public class Example
{
   public static void Main()
   {
      DateTime dateValue = new DateTime(2008, 6, 11);
      Console.WriteLine(dateValue.ToString("ddd"));
   }
}
// The example displays the following output:
 //       Wed

Module Example
    Public Sub Main()
        Dim dateValue As Date = #6/11/2008#
        Console.WriteLine(dateValue.ToString("ddd"))
    End Sub
End Module
' The example displays the following output:
'       Wed

若要提取特定区域性的缩写的星期几名称，请调用日期和时间值的 DateTime.ToString(String, IFormatProvider) 或 DateTimeOffset.ToString(String, IFormatProvider) 实例方法。同时以 format 参数形式传递字符串 ddd。以 CultureInfo 参数的形式传递表示要检索其星期几名称的区域性的 DateTimeFormatInfo 或 provider 对象。下面的代码阐释如何使用表示 fr-FR 区域性的 ToString(String, IFormatProvider) 对象调用 CultureInfo 方法：

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      DateTime dateValue = new DateTime(2008, 6, 11);
      Console.WriteLine(dateValue.ToString("ddd",
                        new CultureInfo("fr-FR")));
   }
}
// The example displays the following output:
//       mer.

Imports System.Globalization

Module Example
    Public Sub Main()
        Dim dateValue As Date = #6/11/2008#
        Console.WriteLine(dateValue.ToString("ddd",
                          New CultureInfo("fr-FR")))
    End Sub
End Module
' The example displays the following output:
'       mer.

提取完整的工作日名称

使用静态 DateTime.Parse 或 DateTimeOffset.Parse 方法将日期的字符串表示形式转换为 DateTime 或 DateTimeOffset 值。

你可以提取当前区域性或特定区域性的完整的星期几名称：

若要提取当前区域性的缩写的星期几名称，请调用日期和时间值的 DateTime.ToString(String) 或 DateTimeOffset.ToString(String) 实例方法，并以 format 参数的形式传递字符串 dddd。下面的示例演示 ToString(String) 方法的调用：

using System;

public class Example
{
   public static void Main()
   {
      DateTime dateValue = new DateTime(2008, 6, 11);
      Console.WriteLine(dateValue.ToString("dddd"));
   }
}
// The example displays the following output:
//       Wednesday

Module Example
    Public Sub Main()
        Dim dateValue As Date = #6/11/2008#
        Console.WriteLine(dateValue.ToString("dddd"))
    End Sub
End Module
' The example displays the following output:
'       Wednesday

若要提取特定区域性的星期几名称，请调用日期和时间值的 DateTime.ToString(String, IFormatProvider) 或 DateTimeOffset.ToString(String, IFormatProvider) 实例方法。同时以 format 参数形式传递字符串 dddd。以 CultureInfo 参数的形式传递表示要检索其星期几名称的区域性的 DateTimeFormatInfo 或 provider 对象。下面的代码阐释如何使用表示 es-ES 区域性的 ToString(String, IFormatProvider) 对象调用 CultureInfo 方法：

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      DateTime dateValue = new DateTime(2008, 6, 11);
      Console.WriteLine(dateValue.ToString("dddd",
                        new CultureInfo("es-ES")));
   }
}
// The example displays the following output:
//       miércoles.

Imports System.Globalization

Module Example
    Public Sub Main()
        Dim dateValue As Date = #6/11/2008#
        Console.WriteLine(dateValue.ToString("dddd", _
                          New CultureInfo("es-ES")))
    End Sub
End Module
' The example displays the following output:
'       miércoles.

示例

以下示例演示如何调用 DateTime.DayOfWeek 和 DateTimeOffset.DayOfWeek 属性，以检索特定日期中表示星期几的数字。它还包括调用 DateTime.ToString 和 DateTimeOffset.ToString 方法来提取缩写的星期几名称和完整的星期几名称。

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      string dateString = "6/11/2007";
      DateTime dateValue;
      DateTimeOffset dateOffsetValue;

      try
      {
         DateTimeFormatInfo dateTimeFormats;
         // Convert date representation to a date value
         dateValue = DateTime.Parse(dateString, CultureInfo.InvariantCulture);
         dateOffsetValue = new DateTimeOffset(dateValue,
                                      TimeZoneInfo.Local.GetUtcOffset(dateValue));

         // Convert date representation to a number indicating the day of week
         Console.WriteLine((int) dateValue.DayOfWeek);
         Console.WriteLine((int) dateOffsetValue.DayOfWeek);

         // Display abbreviated weekday name using current culture
         Console.WriteLine(dateValue.ToString("ddd"));
         Console.WriteLine(dateOffsetValue.ToString("ddd"));

         // Display full weekday name using current culture
         Console.WriteLine(dateValue.ToString("dddd"));
         Console.WriteLine(dateOffsetValue.ToString("dddd"));

         // Display abbreviated weekday name for de-DE culture
         Console.WriteLine(dateValue.ToString("ddd", new CultureInfo("de-DE")));
         Console.WriteLine(dateOffsetValue.ToString("ddd",
                                                     new CultureInfo("de-DE")));

         // Display abbreviated weekday name with de-DE DateTimeFormatInfo object
         dateTimeFormats = new CultureInfo("de-DE").DateTimeFormat;
         Console.WriteLine(dateValue.ToString("ddd", dateTimeFormats));
         Console.WriteLine(dateOffsetValue.ToString("ddd", dateTimeFormats));

         // Display full weekday name for fr-FR culture
         Console.WriteLine(dateValue.ToString("ddd", new CultureInfo("fr-FR")));
         Console.WriteLine(dateOffsetValue.ToString("ddd",
                                                    new CultureInfo("fr-FR")));

         // Display abbreviated weekday name with fr-FR DateTimeFormatInfo object
         dateTimeFormats = new CultureInfo("fr-FR").DateTimeFormat;
         Console.WriteLine(dateValue.ToString("dddd", dateTimeFormats));
         Console.WriteLine(dateOffsetValue.ToString("dddd", dateTimeFormats));
      }
      catch (FormatException)
      {
         Console.WriteLine("Unable to convert {0} to a date.", dateString);
      }
   }
}
// The example displays the following output:
//       1
//       1
//       Mon
//       Mon
//       Monday
//       Monday
//       Mo
//       Mo
//       Mo
//       Mo
//       lun.
//       lun.
//       lundi
//       lundi

Imports System.Globalization

Module Example
    Public Sub Main()
        Dim dateString As String = "6/11/2007"
        Dim dateValue As Date
        Dim dateOffsetValue As DateTimeOffset

        Try
            Dim dateTimeFormats As DateTimeFormatInfo
            ' Convert date representation to a date value
            dateValue = Date.Parse(dateString, CultureInfo.InvariantCulture)
            dateOffsetValue = New DateTimeOffset(dateValue, _
                                        TimeZoneInfo.Local.GetUtcOffset(dateValue))
            ' Convert date representation to a number indicating the day of week
            Console.WriteLine(dateValue.DayOfWeek)
            Console.WriteLine(dateOffsetValue.DayOfWeek)

            ' Display abbreviated weekday name using current culture
            Console.WriteLine(dateValue.ToString("ddd"))
            Console.WriteLine(dateOffsetValue.ToString("ddd"))

            ' Display full weekday name using current culture
            Console.WriteLine(dateValue.ToString("dddd"))
            Console.WriteLine(dateOffsetValue.ToString("dddd"))

            ' Display abbreviated weekday name for de-DE culture
            Console.WriteLine(dateValue.ToString("ddd", New CultureInfo("de-DE")))
            Console.WriteLine(dateOffsetValue.ToString("ddd", _
                                                       New CultureInfo("de-DE")))

            ' Display abbreviated weekday name with de-DE DateTimeFormatInfo object
            dateTimeFormats = New CultureInfo("de-DE").DateTimeFormat
            Console.WriteLine(dateValue.ToString("ddd", dateTimeFormats))
            Console.WriteLine(dateOffsetValue.ToString("ddd", dateTimeFormats))

            ' Display full weekday name for fr-FR culture
            Console.WriteLine(dateValue.ToString("ddd", New CultureInfo("fr-FR")))
            Console.WriteLine(dateOffsetValue.ToString("ddd", _
                                                       New CultureInfo("fr-FR")))

            ' Display abbreviated weekday name with fr-FR DateTimeFormatInfo object
            dateTimeFormats = New CultureInfo("fr-FR").DateTimeFormat
            Console.WriteLine(dateValue.ToString("dddd", dateTimeFormats))
            Console.WriteLine(dateOffsetValue.ToString("dddd", dateTimeFormats))
        Catch e As FormatException
            Console.WriteLine("Unable to convert {0} to a date.", dateString)
        End Try
    End Sub
End Module
' The example displays the following output to the console:
'       1
'       1
'       Mon
'       Mon
'       Monday
'       Monday
'       Mo
'       Mo
'       Mo
'       Mo
'       lun.
'       lun.
'       lundi
'       lundi

个别语言可能提供与 .NET 所提供的功能相同或互为补充的功能。例如，Visual Basic 包括这样的两个函数：

Weekday，它返回指示特定日期中表示星期几的数字。此函数将一周中第一天的序数值视为一，而 DateTime.DayOfWeek 属性却将其视为零。
WeekdayName，它返回当前区域性中与特定星期几相对应的周的名称。

下面的示例演示了 Visual Basic Weekday 和 WeekdayName 函数的用法：

Imports System.Globalization
Imports System.Threading

Module Example
    Public Sub Main()
        Dim dateValue As Date = #6/11/2008#

        ' Get weekday number using Visual Basic Weekday function
        Console.WriteLine(Weekday(dateValue))                 ' Displays 4
        ' Compare with .NET DateTime.DayOfWeek property
        Console.WriteLine(dateValue.DayOfWeek)                ' Displays 3

        ' Get weekday name using Weekday and WeekdayName functions
        Console.WriteLine(WeekdayName(Weekday(dateValue)))    ' Displays Wednesday

        ' Change culture to de-DE
        Dim originalCulture As CultureInfo = Thread.CurrentThread.CurrentCulture
        Thread.CurrentThread.CurrentCulture = New CultureInfo("de-DE")
        ' Get weekday name using Weekday and WeekdayName functions
        Console.WriteLine(WeekdayName(Weekday(dateValue)))   ' Displays Donnerstag

        ' Restore original culture
        Thread.CurrentThread.CurrentCulture = originalCulture
    End Sub
End Module

也可以使用 DateTime.DayOfWeek 属性返回的值检索特定日期的星期几名称。此过程只需对 ToString 属性返回的值调用 DayOfWeek 方法。但是，此技术并不生成当前区域性的本地化星期几名称，如下面的示例所示：

using System;
using System.Globalization;
using System.Threading;

public class Example
{
   public static void Main()
   {
      // Change current culture to fr-FR
      CultureInfo originalCulture = Thread.CurrentThread.CurrentCulture;
      Thread.CurrentThread.CurrentCulture = new CultureInfo("fr-FR");

      DateTime dateValue = new DateTime(2008, 6, 11);
      // Display the DayOfWeek string representation
      Console.WriteLine(dateValue.DayOfWeek.ToString());
      // Restore original current culture
      Thread.CurrentThread.CurrentCulture = originalCulture;
   }
}
// The example displays the following output:
//       Wednesday

Imports System.Globalization
Imports System.Threading

Module Example
    Public Sub Main()
        ' Change current culture to fr-FR
        Dim originalCulture As CultureInfo = Thread.CurrentThread.CurrentCulture
        Thread.CurrentThread.CurrentCulture = New CultureInfo("fr-FR")

        Dim dateValue As Date = #6/11/2008#
        ' Display the DayOfWeek string representation
        Console.WriteLine(dateValue.DayOfWeek.ToString())
        ' Restore original current culture
        Thread.CurrentThread.CurrentCulture = originalCulture
    End Sub
End Module
' The example displays the following output:
'       Wednesday

通过

如何：从特定日期中提取星期几

提取指示星期几的数字

提取缩写的工作日名称

提取完整的工作日名称

示例

请参阅

其他资源