保存和还原时区

项目
04/07/2023

TimeZoneInfo 类依赖于注册表来检索预定义的时区数据。但是，注册表是动态结构。此外，操作系统主要使用注册表包含的时区信息来处理当前年份的时间调整和转换。这对依赖于准确时区数据的应用程序有两个主要影响：

应用程序所需的时区可能未在注册表中定义，或者已重命名或已从注册表中删除。
注册表中定义的时区可能缺少有关历史时区转换所需的特定调整规则的信息。

TimeZoneInfo 类通过支持时区数据的序列化（保存）和反序列化（恢复）来解决这些限制。

时区序列化和反序列化

通过序列化和反序列化时区数据来保存和恢复时区只涉及两个方法调用：

可以通过调用 TimeZoneInfo 对象的 ToSerializedString 方法来序列化该对象。该方法不使用任何参数并返回一个包含时区信息的字符串。
可以通过将该字符串传递给 static（在 Visual Basic 中为 Shared）TimeZoneInfo.FromSerializedString 方法从序列化的字符串反序列化 TimeZoneInfo 对象。

序列化和反序列化场景

能够将 TimeZoneInfo 对象保存（或序列化）为字符串并将其还原（或反序列化）以供以后使用增加了 TimeZoneInfo 类的实用性和灵活性。本部分介绍序列化和反序列化最有用的一些情况。

在应用程序中序列化和反序列化时区数据

如果需要，可以从字符串还原序列化的时区。如果从注册表中检索到的时区无法正确转换特定日期范围内的日期和时间，则应用程序可能会执行此操作。例如，Windows XP 注册表中的时区数据支持单个调整规则，而 Windows Vista 注册表中定义的时区通常提供有关两个调整规则的信息。这意味着历史时间转换可能不准确。时区数据的序列化和反序列化可以解决此限制。

在下面的示例中，不带调整规则的自定义 TimeZoneInfo 类定义为表示从 1883 年到 1917 年（在引入夏时制之前）的美国东部标准时区。自定义时区在具有全局范围的变量中序列化。时区转换方法 ConvertUtcTime 传递协调世界时 (UTC) 时间进行转换。如果日期和时间发生在 1917 年或更早，则自定义东部标准时区从序列化的字符串还原，并替换从注册表中检索到的时区。

using System;

public class TimeZoneSerialization
{
   static string serializedEst;

   public static void Main()
   {
      // Retrieve Eastern Standard Time zone from registry
      try
      {
         TimeZoneSerialization tzs = new TimeZoneSerialization();
         TimeZoneInfo est = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
         // Create custom Eastern Time Zone for historical (pre-1918) conversions
         CreateTimeZone();
         // Call conversion function with one current and one pre-1918 date and time
         Console.WriteLine(ConvertUtcTime(DateTime.UtcNow, est));
         Console.WriteLine(ConvertUtcTime(new DateTime(1900, 11, 15, 9, 32, 00, DateTimeKind.Utc), est));
      }
      catch (TimeZoneNotFoundException)
      {
         Console.WriteLine("The Eastern Standard Time zone is not in the registry.");
      }
      catch (InvalidTimeZoneException)
      {
         Console.WriteLine("Data on the Eastern Standard Time Zone in the registry is corrupted.");
      }
   }

   private static void CreateTimeZone()
   {
      // Create a simple Eastern Standard time zone
      // without adjustment rules for 1883-1918
      TimeZoneInfo earlyEstZone = TimeZoneInfo.CreateCustomTimeZone("Eastern Standard Time",
                                      new TimeSpan(-5, 0, 0),
                                      " (GMT-05:00) Eastern Time (United States)",
                                      "Eastern Standard Time");
      serializedEst = earlyEstZone.ToSerializedString();
   }

   private static DateTime ConvertUtcTime(DateTime utcDate, TimeZoneInfo tz)
   {
      // Use time zone object from registry
      if (utcDate.Year > 1917)
      {
         return TimeZoneInfo.ConvertTimeFromUtc(utcDate, tz);
      }
      // Handle dates before introduction of DST
      else
      {
         // Restore serialized time zone object
         tz = TimeZoneInfo.FromSerializedString(serializedEst);
         return TimeZoneInfo.ConvertTimeFromUtc(utcDate, tz);
      }
   }
}

Module TimeZoneSerialization
    Dim serializedEst As String

    Public Sub Main()
        ' Retrieve Eastern Standard Time zone from registry
        Try
            Dim est As TimeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time")
            ' Create custom Eastern Time Zone for historical (pre-1918) conversions
            CreateTimeZone()
            ' Call conversion function with one current and one pre-1918 date and time
            Console.WriteLine(ConvertUtcTime(Date.UtcNow, est))
            Console.WriteLine(ConvertUtcTime(New Date(1900, 11, 15, 9, 32, 00, DateTimeKind.Utc), est))
        Catch e As TimeZoneNotFoundException
            Console.WriteLine("The Eastern Standard Time zone is not in the registry.")
        Catch e As InvalidTimeZoneException
            Console.WriteLine("Data on the Eastern Standard Time Zone in the registry is corrupted.")
        End Try
    End Sub

    Private Sub CreateTimeZone()
        ' Create a simple Eastern Standard time zone 
        ' without adjustment rules for 1883-1918
        Dim earlyEstZone As TimeZoneInfo = TimeZoneInfo.CreateCustomTimeZone("Eastern Standard Time", _
                                        New TimeSpan(-5, 0, 0), _
                                        " (GMT-05:00) Eastern Time (United States)", _
                                        "Eastern Standard Time")
        serializedEst = earlyEstZone.ToSerializedString()
    End Sub

    Private Function ConvertUtcTime(utcDate As Date, tz As TimeZoneInfo) As Date
        ' Use time zone object from registry 
        If Year(utcDate) > 1917 Then
            Return TimeZoneInfo.ConvertTimeFromUtc(utcDate, tz)
            ' Handle dates before introduction of DST
        Else
            ' Restore serialized time zone object
            tz = TimeZoneInfo.FromSerializedString(serializedEst)
            Return TimeZoneInfo.ConvertTimeFromUtc(utcDate, tz)
        End If
    End Function
End Module

处理时区异常

由于注册表是动态结构，因此其内容可能会遭遇意外或有意修改。这意味着应在注册表中定义并且应用程序成功执行所需的时区可能不存在。如果不支持时区序列化和反序列化，则只能选择通过结束应用程序来处理生成的 TimeZoneNotFoundException。但是，通过使用时区序列化和反序列化，可以通过从序列化的字符串还原所需的时区来处理意外的 TimeZoneNotFoundException，并且应用程序将继续运行。

以下示例创建并序列化自定义中央标准时区。然后，它会尝试从注册表中检索中央标准时区。如果检索操作引发 TimeZoneNotFoundException 或 InvalidTimeZoneException，则异常处理程序会反序列化时区。

using System;
using System.Collections.Generic;

public class TimeZoneApplication
{
   // Define collection of custom time zones
   private Dictionary<string, string> customTimeZones = new Dictionary<string, string>();
   private TimeZoneInfo cst;

   public TimeZoneApplication()
   {
      // Create custom Central Standard Time
      //
      // Declare necessary TimeZoneInfo.AdjustmentRule objects for time zone
      TimeZoneInfo customTimeZone;
      TimeSpan delta = new TimeSpan(1, 0, 0);
      TimeZoneInfo.AdjustmentRule adjustment;
      List<TimeZoneInfo.AdjustmentRule> adjustmentList = new List<TimeZoneInfo.AdjustmentRule>();
      // Declare transition time variables to hold transition time information
      TimeZoneInfo.TransitionTime transitionRuleStart, transitionRuleEnd;

      // Define end rule (for 1976-2006)
      transitionRuleEnd = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(new DateTime(1, 1, 1, 2, 0, 0), 10, 5, DayOfWeek.Sunday);
      // Define rule (1976-1986)
      transitionRuleStart = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(new DateTime(1, 1, 1, 2, 0, 0), 04, 05, DayOfWeek.Sunday);
      adjustment = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(new DateTime(1976, 1, 1), new DateTime(1986, 12, 31), delta, transitionRuleStart, transitionRuleEnd);
      adjustmentList.Add(adjustment);
      // Define rule (1987-2006)
      transitionRuleStart = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(new DateTime(1, 1, 1, 2, 0, 0), 04, 01, DayOfWeek.Sunday);
      adjustment = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(new DateTime(1987, 1, 1), new DateTime(2006, 12, 31), delta, transitionRuleStart, transitionRuleEnd);
      adjustmentList.Add(adjustment);
      // Define rule (2007- )
      transitionRuleStart = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(new DateTime(1, 1, 1, 2, 0, 0), 03, 02, DayOfWeek.Sunday);
      transitionRuleEnd = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(new DateTime(1, 1, 1, 2, 0, 0), 11, 01, DayOfWeek.Sunday);
      adjustment = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(new DateTime(2007, 01, 01), DateTime.MaxValue.Date, delta, transitionRuleStart, transitionRuleEnd);
      adjustmentList.Add(adjustment);

      // Create custom U.S. Central Standard Time zone
      customTimeZone = TimeZoneInfo.CreateCustomTimeZone("Central Standard Time",
                      new TimeSpan(-6, 0, 0),
                      "(GMT-06:00) Central Time (US Only)", "Central Standard Time",
                      "Central Daylight Time", adjustmentList.ToArray());
      // Add time zone to collection
      customTimeZones.Add(customTimeZone.Id, customTimeZone.ToSerializedString());

      // Create any other required time zones
   }

   public static void Main()
   {
      TimeZoneApplication tza = new TimeZoneApplication();
      tza.AppEntryPoint();
   }

   private void AppEntryPoint()
   {
      try
      {
         cst = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
      }
      catch (TimeZoneNotFoundException)
      {
         if (customTimeZones.ContainsKey("Central Standard Time"))
            HandleTimeZoneException("Central Standard Time");
      }
      catch (InvalidTimeZoneException)
      {
         if (customTimeZones.ContainsKey("Central Standard Time"))
            HandleTimeZoneException("Central Standard Time");
      }
      if (cst == null)
      {
         Console.WriteLine("Unable to load Central Standard Time zone.");
         return;
      }
      DateTime currentTime = DateTime.Now;
      Console.WriteLine("The current {0} time is {1}.",
                        TimeZoneInfo.Local.IsDaylightSavingTime(currentTime) ?
                            TimeZoneInfo.Local.StandardName :
                            TimeZoneInfo.Local.DaylightName,
                        currentTime.ToString("f"));
      Console.WriteLine("The current {0} time is {1}.",
                        cst.IsDaylightSavingTime(currentTime) ?
                            cst.StandardName :
                            cst.DaylightName,
                        TimeZoneInfo.ConvertTime(currentTime, TimeZoneInfo.Local, cst).ToString("f"));
   }

   private void HandleTimeZoneException(string timeZoneName)
   {
      string tzString = customTimeZones[timeZoneName];
      cst = TimeZoneInfo.FromSerializedString(tzString);
   }
}

Imports System.Collections.Generic

Public Class TimeZoneApplication
    ' Define collection of custom time zones
    Private customTimeZones As New Dictionary(Of String, String)
    Private cst As TimeZoneInfo

    Public Sub New()
        ' Define custom Central Standard Time
        '
        ' Declare necessary TimeZoneInfo.AdjustmentRule objects for time zone
        Dim customTimeZone As TimeZoneInfo
        Dim delta As New TimeSpan(1, 0, 0)
        Dim adjustment As TimeZoneInfo.AdjustmentRule
        Dim adjustmentList As New List(Of TimeZoneInfo.AdjustmentRule)
        ' Declare transition time variables to hold transition time information
        Dim transitionRuleStart, transitionRuleEnd As TimeZoneInfo.TransitionTime

        ' Define end rule (for 1976-2006)
        transitionRuleEnd = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(#02:00:00AM#, 10, 5, DayOfWeek.Sunday)
        ' Define rule (1976-1986)
        transitionRuleStart = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(#2:00:00AM#, 04, 05, DayOfWeek.Sunday)
        adjustment = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(#01/01/1976#, #12/31/1986#, delta, transitionRuleStart, transitionRuleEnd)
        adjustmentList.Add(adjustment)
        ' Define rule (1987-2006)  
        transitionRuleStart = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(#2:00:00AM#, 04, 01, DayOfWeek.Sunday)
        adjustment = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(#01/01/1987#, #12/31/2006#, delta, transitionRuleStart, transitionRuleEnd)
        adjustmentList.Add(adjustment)
        ' Define rule (2007- )  
        transitionRuleStart = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(#2:00:00AM#, 03, 02, DayOfWeek.Sunday)
        transitionRuleEnd = TimeZoneInfo.TransitionTime.CreateFloatingDateRule(#2:00:00AM#, 11, 01, DayOfWeek.Sunday)
        adjustment = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(#01/01/2007#, Date.MaxValue.Date, delta, transitionRuleStart, transitionRuleEnd)
        adjustmentList.Add(adjustment)
        ' Create custom time zone
        customTimeZone = TimeZoneInfo.CreateCustomTimeZone("Central Standard Time", _
                        New TimeSpan(-6, 0, 0), _
                        "(GMT-06:00) Central Time (US Only)", "Central Standard Time", _
                        "Central Daylight Time", adjustmentList.ToArray())
        ' Add time zone to collection
        customTimeZones.Add(customTimeZone.Id, customTimeZone.ToSerializedString())

        ' Create any other required time zones     
    End Sub

    Public Shared Sub Main()
        Dim tza As New TimeZoneApplication()
        tza.AppEntryPoint()
    End Sub

    Private Sub AppEntryPoint()
        Try
            cst = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time")
        Catch e As TimeZoneNotFoundException
            If customTimeZones.ContainsKey("Central Standard Time")
                HandleTimeZoneException("Central Standard Time")
            End If
        Catch e As InvalidTimeZoneException
            If customTimeZones.ContainsKey("Central Standard Time")
                HandleTimeZoneException("Central Standard Time")
            End If
        End Try
        If cst Is Nothing Then
            Console.WriteLine("Unable to load Central Standard Time zone.")
            Return
        End If
        Dim currentTime As Date = Date.Now
        Console.WriteLine("The current {0} time is {1}.", _
                          IIf(TimeZoneInfo.Local.IsDaylightSavingTime(currentTime), _
                              TimeZoneInfo.Local.StandardName, _
                              TimeZoneInfo.Local.DaylightName), _
                          currentTime.ToString("f"))
        Console.WriteLine("The current {0} time is {1}.", _
                          IIf(cst.IsDaylightSavingTime(currentTime), _
                              cst.StandardName, _
                              cst.DaylightName), _
                          TimeZoneInfo.ConvertTime(currentTime, TimeZoneInfo.Local, cst).ToString("f"))
    End Sub

    Private Sub HandleTimeZoneException(timeZoneName As String)
        Dim tzString As String = customTimeZones.Item(timeZoneName)
        cst = TimeZoneInfo.FromSerializedString(tzString)
    End Sub
End Class

存储序列化的字符串并根据需要还原它

前面的示例将时区信息存储到字符串变量中，并根据需要将其还原。但是，包含序列化的时区信息的字符串本身可以存储在某些存储介质中，例如外部文件、嵌入在应用程序中的资源文件或注册表。（请注意，有关自定义时区的信息应与注册表中系统的时区键分开存储。）

以此方式存储序列化的时区字符串还会将时区创建例程与应用程序本身分开。例如，时区创建例程可以执行并创建一个数据文件，其中包含应用程序可以使用的历史时区信息。然后，可以将该数据文件与应用程序一起安装，当应用程序需要时，可以打开该文件并反序列化其一个或多个时区。

有关使用嵌入的资源来存储序列化时区数据的示例，请参阅如何：将时区保存到嵌入的资源中和如何：从嵌入的资源还原时区。

另请参阅

日期、时间和时区

通过