作法：在日期和時間算術中使用時區

發行項
06/08/2024

一般來說，當您使用 DateTime 或 DateTimeOffset 值執行日期與時間算術時，結果不會反映任何時區調整規則。即使日期與時間值的時區可清楚識別 (例如，將 Kind 屬性設定為 Local 時)，也是如此。本文顯示如何對屬於特定時區的日期與時間值執行算術運算。算術運算的結果將反映時區調整規則。

將調整規則套用至日期和時間運算

實作某種方法，以將日期和時間值與所屬時區緊密結合。例如，宣告包含日期和時間值及其時區的結構。下列範例使用此方式來連結 DateTime 值及其時區。

// Define a structure for DateTime values for internal use only
internal struct TimeWithTimeZone
{
   TimeZoneInfo TimeZone;
   DateTime Time;
}

' Define a structure for DateTime values for internal use only
Friend Structure TimeWithTimeZone
    Dim TimeZone As TimeZoneInfo
    Dim Time As Date
End Structure

藉由呼叫 ConvertTimeToUtc 方法或 ConvertTime 方法，將時間轉換成國際標準時間 (UTC)。
對 UTC 時間執行算術運算。
藉由呼叫 TimeZoneInfo.ConvertTime(DateTime, TimeZoneInfo) 方法，將時間從 UTC 轉換成原始時間的相關時區。

範例

下列範例將兩個小時三十分鐘新增至 2008 年 3 月 9 日凌晨 1:30中央標準時區。時區轉換為日光節約時間會在三十分鐘後，也就是 2008 年 3 月 9 日上午 2:00 發生。由於本範例依照上一節所列的四個步驟進行，因此會正確回報產生的時間 2008 年 3 月 9 日上午 5:00。

using System;

public struct TimeZoneTime
{
   public TimeZoneInfo TimeZone;
   public DateTime Time;

   public TimeZoneTime(TimeZoneInfo tz, DateTime time)
   {
      if (tz == null)
         throw new ArgumentNullException("The time zone cannot be a null reference.");

      this.TimeZone = tz;
      this.Time = time;
   }

   public TimeZoneTime AddTime(TimeSpan interval)
   {
      // Convert time to UTC
      DateTime utcTime = TimeZoneInfo.ConvertTimeToUtc(this.Time, this.TimeZone);
      // Add time interval to time
      utcTime = utcTime.Add(interval);
      // Convert time back to time in time zone
      return new TimeZoneTime(this.TimeZone, TimeZoneInfo.ConvertTime(utcTime,
                              TimeZoneInfo.Utc, this.TimeZone));
   }
}

public class TimeArithmetic
{
   public const string tzName = "Central Standard Time";

   public static void Main()
   {
      try
      {
         TimeZoneTime cstTime1, cstTime2;

         TimeZoneInfo cst = TimeZoneInfo.FindSystemTimeZoneById(tzName);
         DateTime time1 = new DateTime(2008, 3, 9, 1, 30, 0);
         TimeSpan twoAndAHalfHours = new TimeSpan(2, 30, 0);

         cstTime1 = new TimeZoneTime(cst, time1);
         cstTime2 = cstTime1.AddTime(twoAndAHalfHours);
         Console.WriteLine("{0} + {1} hours = {2}", cstTime1.Time,
                                                    twoAndAHalfHours.ToString(),
                                                    cstTime2.Time);
      }
      catch
      {
         Console.WriteLine("Unable to find {0}.", tzName);
      }
   }
}

Public Structure TimeZoneTime
    Public TimeZone As TimeZoneInfo
    Public Time As Date

    Public Sub New(tz As TimeZoneInfo, time As Date)
        If tz Is Nothing Then _
           Throw New ArgumentNullException("The time zone cannot be a null reference.")

        Me.TimeZone = tz
        Me.Time = time
    End Sub

    Public Function AddTime(interval As TimeSpan) As TimeZoneTime
        ' Convert time to UTC
        Dim utcTime As DateTime = TimeZoneInfo.ConvertTimeToUtc(Me.Time, _
                                                                Me.TimeZone)
        ' Add time interval to time
        utcTime = utcTime.Add(interval)
        ' Convert time back to time in time zone
        Return New TimeZoneTime(Me.TimeZone, TimeZoneInfo.ConvertTime(utcTime, _
                                TimeZoneInfo.Utc, Me.TimeZone))
    End Function
End Structure

Module TimeArithmetic
    Public Const tzName As String = "Central Standard Time"

    Public Sub Main()
        Try
            Dim cstTime1, cstTime2 As TimeZoneTime

            Dim cst As TimeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById(tzName)
            Dim time1 As Date = #03/09/2008 1:30AM#
            Dim twoAndAHalfHours As New TimeSpan(2, 30, 0)

            cstTime1 = New TimeZoneTime(cst, time1)
            cstTime2 = cstTime1.AddTime(twoAndAHalfHours)

            Console.WriteLine("{0} + {1} hours = {2}", cstTime1.Time, _
                                                       twoAndAHalfHours.ToString(), _
                                                       cstTime2.Time)
        Catch
            Console.WriteLine("Unable to find {0}.", tzName)
        End Try
    End Sub
End Module

DateTime 與 DateTimeOffset 值會與任何其可能所屬的時區解除關聯。若要透過自動套用時區調整規則來執行日期和時間運算，則必須立即識別任何日期和時間值所屬的時區。這表示日期和時間及其相關聯時區必須緊密結合。有幾個方式可做到這點，包括下列各項︰

假設應用程式中使用的所有時間都是屬於特定時區。雖然適用於某些情況，但是這種方式提供的彈性有限，可攜性也可能有限。
定義一種類型，而這個類型透過將日期和時間與其相關聯時區都包含為類型的欄位來緊密結合兩者。程式碼範例中使用這種方式，以定義將日期和時間以及時區儲存在兩個成員欄位中的結構。

此範例說明如何對 DateTime 值執行算數運算，以便將時區調整規則套用至結果。然而，同樣也可輕易地使用 DateTimeOffset 值。下列範例說明原始範例中的程式碼如何調整為使用 DateTimeOffset，而不是 DateTime 值。

using System;

public struct TimeZoneTime
{
   public TimeZoneInfo TimeZone;
   public DateTimeOffset Time;

   public TimeZoneTime(TimeZoneInfo tz, DateTimeOffset time)
   {
      if (tz == null)
         throw new ArgumentNullException("The time zone cannot be a null reference.");

      this.TimeZone = tz;
      this.Time = time;
   }

   public TimeZoneTime AddTime(TimeSpan interval)
   {
      // Convert time to UTC
      DateTimeOffset utcTime = TimeZoneInfo.ConvertTime(this.Time, TimeZoneInfo.Utc);
      // Add time interval to time
      utcTime = utcTime.Add(interval);
      // Convert time back to time in time zone
      return new TimeZoneTime(this.TimeZone, TimeZoneInfo.ConvertTime(utcTime, this.TimeZone));
   }
}

public class TimeArithmetic
{
   public const string tzName = "Central Standard Time";

   public static void Main()
   {
      try
      {
         TimeZoneTime cstTime1, cstTime2;

         TimeZoneInfo cst = TimeZoneInfo.FindSystemTimeZoneById(tzName);
         DateTime time1 = new DateTime(2008, 3, 9, 1, 30, 0);
         TimeSpan twoAndAHalfHours = new TimeSpan(2, 30, 0);

         cstTime1 = new TimeZoneTime(cst,
                        new DateTimeOffset(time1, cst.GetUtcOffset(time1)));
         cstTime2 = cstTime1.AddTime(twoAndAHalfHours);
         Console.WriteLine("{0} + {1} hours = {2}", cstTime1.Time,
                                                    twoAndAHalfHours.ToString(),
                                                    cstTime2.Time);
      }
      catch
      {
         Console.WriteLine("Unable to find {0}.", tzName);
      }
   }
}

Public Structure TimeZoneTime
    Public TimeZone As TimeZoneInfo
    Public Time As DateTimeOffset

    Public Sub New(tz As TimeZoneInfo, time As DateTimeOffset)
        If tz Is Nothing Then _
           Throw New ArgumentNullException("The time zone cannot be a null reference.")

        Me.TimeZone = tz
        Me.Time = time
    End Sub

    Public Function AddTime(interval As TimeSpan) As TimeZoneTime
        ' Convert time to UTC
        Dim utcTime As DateTimeOffset = TimeZoneInfo.ConvertTime(Me.Time, TimeZoneInfo.Utc)
        ' Add time interval to time
        utcTime = utcTime.Add(interval)
        ' Convert time back to time in time zone
        Return New TimeZoneTime(Me.TimeZone, TimeZoneInfo.ConvertTime(utcTime, Me.TimeZone))
    End Function
End Structure

Module TimeArithmetic
    Public Const tzName As String = "Central Standard Time"

    Public Sub Main()
        Try
            Dim cstTime1, cstTime2 As TimeZoneTime

            Dim cst As TimeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById(tzName)
            Dim time1 As Date = #03/09/2008 1:30AM#
            Dim twoAndAHalfHours As New TimeSpan(2, 30, 0)

            cstTime1 = New TimeZoneTime(cst, _
                           New DateTimeOffset(time1, cst.GetUtcOffset(time1)))
            cstTime2 = cstTime1.AddTime(twoAndAHalfHours)

            Console.WriteLine("{0} + {1} hours = {2}", cstTime1.Time, _
                                                       twoAndAHalfHours.ToString(), _
                                                       cstTime2.Time)
        Catch
            Console.WriteLine("Unable to find {0}.", tzName)
        End Try
    End Sub
End Module

請注意，若此加法只會對 DateTimeOffset 值執行，而不需要先將其轉換成 UTC，則結果會反映正確時間點，但其位移不會反映該時間所指定時區的位移。

共用方式為

作法：在日期和時間算術中使用時區

將調整規則套用至日期和時間運算

範例

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