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操作說明:從特定日期擷取一星期的哪一日

.NET 可方便判斷特定日期是一週的第幾天,並可顯示特定日期當地語系化的工作日名稱。 您可以從 DayOfWeekDayOfWeek 屬性取得指出對應於特定日期是星期幾的列舉值。 相對地,擷取工作日名稱是一種格式化作業,可藉由呼叫格式化方法來執行,例如日期和時間值的 ToString 方法或 String.Format 方法。 本文示範如何執行下列格式化作業。

擷取表示星期幾的數字

  1. 使用靜態 DateTime.ParseDateTimeOffset.Parse 方法,將日期的字串表示轉換成 DateTimeDateTimeOffset 值。

  2. 使用 DateTime.DayOfWeekDateTimeOffset.DayOfWeek 屬性,以擷取指出星期幾的 DayOfWeek 值。

  3. 若有需要,可將 DayOfWeek 值轉型 (在 C# 中) 或轉換 (在 Visual Basic 中) 成整數。

下列範例顯示代表特定日期是星期幾的整數:

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

擷取工作日名稱縮寫

  1. 使用靜態 DateTime.ParseDateTimeOffset.Parse 方法,將日期的字串表示轉換成 DateTimeDateTimeOffset 值。

  2. 您可以擷取目前文化特性或特定文化特性的工作日名稱縮寫。

    1. 若要擷取目前文化特性的工作日名稱縮寫,請呼叫日期和時間值的 DateTime.ToString(String)DateTimeOffset.ToString(String) 執行個體方法,並傳遞字串 ddd 做為 format 參數。 下列範例說明如何呼叫 ToString(String) 方法:

      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
      
    2. 若要擷取特定文化特性的工作日名稱縮寫,請呼叫日期和時間值的 DateTime.ToString(String, IFormatProvider)DateTimeOffset.ToString(String, IFormatProvider) 執行個體方法。 傳遞字串 ddd 做為 format 參數。 傳遞 CultureInfoDateTimeFormatInfo 物件,其代表您想要將其工作日名稱當作 provider 參數來擷取的文化特性。 下列程式碼說明如何使用代表 fr-FR 文化特性的 CultureInfo 物件,來呼叫 ToString(String, IFormatProvider) 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.
      

擷取完整的工作日名稱

  1. 使用靜態 DateTime.ParseDateTimeOffset.Parse 方法,將日期的字串表示轉換成 DateTimeDateTimeOffset 值。

  2. 您可以擷取目前文化特性或特定文化特性的完整工作日名稱。

    1. 若要擷取目前文化特性的工作日名稱,請呼叫日期和時間值的 DateTime.ToString(String)DateTimeOffset.ToString(String) 執行個體方法,並傳遞字串 dddd 做為 format 參數。 下列範例說明如何呼叫 ToString(String) 方法:

      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
      
    2. 若要擷取特定文化特性的工作日名稱,請呼叫日期和時間值的 DateTime.ToString(String, IFormatProvider)DateTimeOffset.ToString(String, IFormatProvider) 執行個體方法。 傳遞字串 dddd 做為 format 參數。 傳遞 CultureInfoDateTimeFormatInfo 物件,其代表您想要將其工作日名稱當作 provider 參數來擷取的文化特性。 下列程式碼說明如何使用代表 es-ES 文化特性的 CultureInfo 物件,來呼叫 ToString(String, IFormatProvider) 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.
      

範例

下列範例說明對 DateTime.DayOfWeekDateTimeOffset.DayOfWeek 屬性的呼叫,用於擷取代表特定日期是星期幾的數字。 也包含呼叫 DateTime.ToStringDateTimeOffset.ToString 方法,以擷取縮寫的工作日名稱和完整的工作日名稱。

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

個別語言可能會提供功能,以複製或補充 .NET 提供的功能。 例如,Visual Basic 就有包含兩個這類函式:

  • Weekday 會傳回指出特定日期是星期幾的數字。 它會將一週第一天的序數值視為一,而 DateTime.DayOfWeek 屬性會將其視為零。

  • WeekdayName 會傳回目前文化特性中對應特定工作日編號的週間日名稱。

下列範例說明如何使用 Visual Basic WeekdayWeekdayName 函式:

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

您也可以使用 DateTime.DayOfWeek 屬性傳回的值來擷取特定日期的工作日名稱。 這個處理程序只需要在該屬性傳回的 DayOfWeek 值上呼叫 ToString 方法。 不過,此技巧並不會產生目前文化特性的當地語系化工作日名稱,如下列範例所說明:

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

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