如何：在日期和时间算术中使用时区

项目
04/07/2023

通常，使用 DateTime 或 DateTimeOffset 值执行日期和时间运算时，结果不会反映任何时区调整规则。即使日期和时间值的时区明确可辨时（例如，将 Kind 属性设置为 Local 时）也是如此。本主题介绍如何对特定时区内的日期和时间值执行算术运算。算术运算的结果将反映时区调整规则。

将调整规则应用到日期和时间运算

采取措施将日期和时间值与其所属时区紧密耦合。例如声明同时包含日期和时间值及其时区的结构。下方示例使用此方法链接 DateTime 值与其时区。

// 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

调用 ConvertTimeToUtc 方法或 ConvertTime 方法，将时间转换为协调世界时 (UTC)。
对 UTC 时间执行算术运算。
调用 TimeZoneInfo.ConvertTime(DateTime, TimeZoneInfo) 方法，将时间从 UTC 转换到与原始时间相关联的时区。

示例

下方示例向中部标准时间 2008 年 3 月 9 日凌晨 1:30 增加了 2 小时 30 分钟。 30 分钟后（即 2008 年 3 月 9 日凌晨 2:00）会发生到夏时令的时区转换。由于该示例遵从了上一部分中列出的四个步骤，因此它将最终时间正确地报告为 2008 年 3 月 9 日凌晨 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 和 DateTimeOffset 值都将与其所属的任何时区解除关联。只有能够立即识别任意日期和时间所属的时区，才能在执行日期和时间运算时自动应用时区调整规则。这意味着，日期和时间及其关联时区必须紧密耦合。可通过方法进行此操作，其中包括：

假设应用程序中使用的所有时间均属于某个特定时区。尽管在某些情况下适用，但此方法的灵活性和可移植性有限。
在类型字段中包括日期和时间及其关联时区，定义将二者紧密耦合的类型。代码示例中使用了此方法，定义了将日期和时间以及时区存储在两个成员字段中的结构。

该示例演示如何对 DateTime 值执行算术运算，以便将时区调整规则应用于结果。但是，可以轻松地使用 DateTimeOffset 值。下面的示例演示如何调整原始示例中的代码，以使用 DateTimeOffset 值（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

请注意，如果未先将 DateTimeOffset 值转换为 UTC 就进行相加，那么结果将反映正确的时间点，但其时差无法反映指定时区在当时的时差。

编译代码

此示例需要：

使用 using 语句导入的 System 命名空间（在 C# 代码中是必需的）。

如何：在日期和时间算术中使用时区

将调整规则应用到日期和时间运算

示例

编译代码

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