在 DateTime 与 DateTimeOffset 之间进行转换

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从 DateTime 转换为 DateTimeOffset

DateTimeOffset 结构提供两种适用于大多数转换的等效方法来执行从 DateTime 到 DateTimeOffset 的转换：

DateTimeOffset 构造函数，它基于 DateTime 值创建新的 DateTimeOffset 对象。

隐式转换运算符，允许将 DateTime 值分配给 DateTimeOffset 对象。

对于 UTC 和本地 DateTime 值，所生成 DateTimeOffset 值的 Offset 属性可准确反映 UTC 或本地时区偏移量。例如，以下代码将 UTC 时间转换为其等效的 DateTimeOffset 值：

DateTime utcTime1 = new DateTime(2008, 6, 19, 7, 0, 0);
utcTime1 = DateTime.SpecifyKind(utcTime1, DateTimeKind.Utc);
DateTimeOffset utcTime2 = utcTime1;
Console.WriteLine("Converted {0} {1} to a DateTimeOffset value of {2}",
                  utcTime1,
                  utcTime1.Kind,
                  utcTime2);
// This example displays the following output to the console:
//    Converted 6/19/2008 7:00:00 AM Utc to a DateTimeOffset value of 6/19/2008 7:00:00 AM +00:00

Dim utcTime1 As Date = Date.SpecifyKind(#06/19/2008 7:00AM#, _
                                        DateTimeKind.Utc)
Dim utcTime2 As DateTimeOffset = utcTime1
Console.WriteLine("Converted {0} {1} to a DateTimeOffset value of {2}", _
                  utcTime1, _
                  utcTime1.Kind.ToString(), _
                  utcTime2)
' This example displays the following output to the console:
'    Converted 6/19/2008 7:00:00 AM Utc to a DateTimeOffset value of 6/19/2008 7:00:00 AM +00:00                        
在本例中，utcTime2 变量的偏移量为 00:00。 同样，以下代码将本地时间转换为其等效的 DateTimeOffset 值：
DateTime localTime1 = new DateTime(2008, 6, 19, 7, 0, 0);
localTime1 = DateTime.SpecifyKind(localTime1, DateTimeKind.Local);
DateTimeOffset localTime2 = localTime1;
Console.WriteLine("Converted {0} {1} to a DateTimeOffset value of {2}",
                  localTime1,
                  localTime1.Kind,
                  localTime2);
// This example displays the following output to the console:
//    Converted 6/19/2008 7:00:00 AM Local to a DateTimeOffset value of 6/19/2008 7:00:00 AM -07:00
Dim localTime1 As Date = Date.SpecifyKind(#06/19/2008 7:00AM#, DateTimeKind.Local)
Dim localTime2 As DateTimeOffset = localTime1
Console.WriteLine("Converted {0} {1} to a DateTimeOffset value of {2}", _
                  localTime1, _
                  localTime1.Kind.ToString(), _
                  localTime2)
' This example displays the following output to the console:
'    Converted 6/19/2008 7:00:00 AM Local to a DateTimeOffset value of 6/19/2008 7:00:00 AM -07:00
但是，对于 Kind 属性为 DateTimeKind.Unspecified 的 DateTime 值，这两种转换方法会生成 DateTimeOffset 值，其偏移量为本地时区的偏移量。 下面的示例对该转换进行了演示，该示例使用美国太平洋标准时区：
DateTime time1 = new DateTime(2008, 6, 19, 7, 0, 0);  // Kind is DateTimeKind.Unspecified
DateTimeOffset time2 = time1;
Console.WriteLine("Converted {0} {1} to a DateTimeOffset value of {2}",
                  time1,
                  time1.Kind,
                  time2);
// This example displays the following output to the console:
//    Converted 6/19/2008 7:00:00 AM Unspecified to a DateTimeOffset value of 6/19/2008 7:00:00 AM -07:00
Dim time1 As Date = #06/19/2008 7:00AM#      ' Kind is DateTimeKind.Unspecified
Dim time2 As DateTimeOffset = time1
Console.WriteLine("Converted {0} {1} to a DateTimeOffset value of {2}", _
                  time1, _
                  time1.Kind.ToString(), _
                  time2)
' This example displays the following output to the console:
'    Converted 6/19/2008 7:00:00 AM Unspecified to a DateTimeOffset value of 6/19/2008 7:00:00 AM -07:00
如果 DateTime 值所反映的不是本地时间或 UTC，可以调用已重载的 DateTimeOffset 构造函数将其转换为 DateTimeOffset 值，并保留其时区信息。 例如，以下示例实例化反映中部标准时间的 DateTimeOffset 对象：
DateTime time1 = new DateTime(2008, 6, 19, 7, 0, 0);     // Kind is DateTimeKind.Unspecified
   DateTimeOffset time2 = new DateTimeOffset(time1,
                  TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time").GetUtcOffset(time1));
   Console.WriteLine("Converted {0} {1} to a DateTime value of {2}",
                     time1,
                     time1.Kind,
                     time2);
// Handle exception if time zone is not defined in registry
catch (TimeZoneNotFoundException)
   Console.WriteLine("Unable to identify target time zone for conversion.");
// This example displays the following output to the console:
//    Converted 6/19/2008 7:00:00 AM Unspecified to a DateTime value of 6/19/2008 7:00:00 AM -05:00
Dim time1 As Date = #06/19/2008 7:00AM#      ' Kind is DateTimeKind.Unspecified
    Dim time2 As New DateTimeOffset(time1, _
                     TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time").GetUtcOffset(time1))
    Console.WriteLine("Converted {0} {1} to a DateTime value of {2}", _
                      time1, _
                      time1.Kind.ToString(), _
                      time2)
    ' Handle exception if time zone is not defined in registry
Catch e As TimeZoneNotFoundException
    Console.WriteLine("Unable to identify target time zone for conversion.")
End Try
' This example displays the following output to the console:
'    Converted 6/19/2008 7:00:00 AM Unspecified to a DateTime value of 6/19/2008 7:00:00 AM -05:00
此构造函数重载的第二个参数是 TimeSpan 对象，该对象表示时间相对于 UTC 的偏移量。 请通过调用时间相应时区的 TimeZoneInfo.GetUtcOffset(DateTime) 方法来对其进行检索。 该方法的单个参数是 DateTime 值，表示要转换的日期和时间。 如果时区支持夏令时，此参数允许方法为该特定日期和时间确定适当偏移量。
从 DateTimeOffset 转换为 DateTime
DateTime 属性最常用于执行 DateTimeOffset 到 DateTime 的转换。 但是，这返回 DateTime 值，其 Kind 属性为 Unspecified，如以下示例所示：
DateTime baseTime = new DateTime(2008, 6, 19, 7, 0, 0);
DateTimeOffset sourceTime;
DateTime targetTime;
// Convert UTC to DateTime value
sourceTime = new DateTimeOffset(baseTime, TimeSpan.Zero);
targetTime = sourceTime.DateTime;
Console.WriteLine("{0} converts to {1} {2}",
                  sourceTime,
                  targetTime,
                  targetTime.Kind);
// Convert local time to DateTime value
sourceTime = new DateTimeOffset(baseTime,
                                TimeZoneInfo.Local.GetUtcOffset(baseTime));
targetTime = sourceTime.DateTime;
Console.WriteLine("{0} converts to {1} {2}",
                  sourceTime,
                  targetTime,
                  targetTime.Kind);
// Convert Central Standard Time to a DateTime value
   TimeSpan offset = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time").GetUtcOffset(baseTime);
   sourceTime = new DateTimeOffset(baseTime, offset);
   targetTime = sourceTime.DateTime;
   Console.WriteLine("{0} converts to {1} {2}",
                     sourceTime,
                     targetTime,
                     targetTime.Kind);
catch (TimeZoneNotFoundException)
   Console.WriteLine("Unable to create DateTimeOffset based on U.S. Central Standard Time.");
// This example displays the following output to the console:
//    6/19/2008 7:00:00 AM +00:00 converts to 6/19/2008 7:00:00 AM Unspecified
//    6/19/2008 7:00:00 AM -07:00 converts to 6/19/2008 7:00:00 AM Unspecified
//    6/19/2008 7:00:00 AM -05:00 converts to 6/19/2008 7:00:00 AM Unspecified
Const baseTime As Date = #06/19/2008 7:00AM#
Dim sourceTime As DateTimeOffset
Dim targetTime As Date
' Convert UTC to DateTime value
sourceTime = New DateTimeOffset(baseTime, TimeSpan.Zero)
targetTime = sourceTime.DateTime
Console.WriteLine("{0} converts to {1} {2}", _
                  sourceTime, _
                  targetTime, _
                  targetTime.Kind.ToString())
' Convert local time to DateTime value
sourceTime = New DateTimeOffset(baseTime, _
                                TimeZoneInfo.Local.GetUtcOffset(baseTime))
targetTime = sourceTime.DateTime
Console.WriteLine("{0} converts to {1} {2}", _
                  sourceTime, _
                  targetTime, _
                  targetTime.Kind.ToString())
' Convert Central Standard Time to a DateTime value
    Dim offset As TimeSpan = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time").GetUtcOffset(baseTime)
    sourceTime = New DateTimeOffset(baseTime, offset)
    targetTime = sourceTime.DateTime
    Console.WriteLine("{0} converts to {1} {2}", _
                      sourceTime, _
                      targetTime, _
                      targetTime.Kind.ToString())
Catch e As TimeZoneNotFoundException
    Console.WriteLine("Unable to create DateTimeOffset based on U.S. Central Standard Time.")
End Try
' This example displays the following output to the console:
'    6/19/2008 7:00:00 AM +00:00 converts to 6/19/2008 7:00:00 AM Unspecified
'    6/19/2008 7:00:00 AM -07:00 converts to 6/19/2008 7:00:00 AM Unspecified
'    6/19/2008 7:00:00 AM -05:00 converts to 6/19/2008 7:00:00 AM Unspecified                       
上一示例演示在使用 DateTime 属性时，转换后会丢失任何有关 DateTimeOffset 值与 UTC 的关系信息。 此行为还会影响对应于 UTC 时间或系统本地时间的 DateTimeOffset 值，因为 DateTime 结构仅会在其 Kind 属性中反映这两个时区。
要在将 DateTimeOffset 转换为 DateTime 值时保留尽可能多的时区信息，可以使用 DateTimeOffset.UtcDateTime 和 DateTimeOffset.LocalDateTime 属性。
转换 UTC 时间
若要指示转换的 DateTime 值是 UTC 时间，可以检索 DateTimeOffset.UtcDateTime 属性的值。 该属性与 DateTime 属性有以下两处不同：
它返回 Kind 属性为 Utc 的 DateTime 值。
如果 Offset 属性值不等于 TimeSpan.Zero，它会将时间转换为 UTC。
如果应用程序需要已转换的 DateTime 值明确标识单个时间点，应考虑使用 DateTimeOffset.UtcDateTime 属性来处理所有从 DateTimeOffset 到 DateTime 的转换。
以下代码使用 UtcDateTime 属性将偏移量等于 TimeSpan.Zero 的 DateTimeOffset 值转换为 DateTime 值：
DateTimeOffset utcTime1 = new DateTimeOffset(2008, 6, 19, 7, 0, 0, TimeSpan.Zero);
DateTime utcTime2 = utcTime1.UtcDateTime;
Console.WriteLine("{0} converted to {1} {2}",
                  utcTime1,
                  utcTime2,
                  utcTime2.Kind);
// The example displays the following output to the console:
//   6/19/2008 7:00:00 AM +00:00 converted to 6/19/2008 7:00:00 AM Utc
Dim utcTime1 As New DateTimeOffset(#06/19/2008 7:00AM#, TimeSpan.Zero)
Dim utcTime2 As Date = utcTime1.UtcDateTime
Console.WriteLine("{0} converted to {1} {2}", _
                  utcTime1, _
                  utcTime2, _
                  utcTime2.Kind.ToString())
' The example displays the following output to the console:
'   6/19/2008 7:00:00 AM +00:00 converted to 6/19/2008 7:00:00 AM Utc                              
以下代码使用 UtcDateTime 属性同时执行时区转换和 DateTimeOffset 值的类型转换：
DateTimeOffset originalTime = new DateTimeOffset(2008, 6, 19, 7, 0, 0, new TimeSpan(5, 0, 0));
DateTime utcTime = originalTime.UtcDateTime;
Console.WriteLine("{0} converted to {1} {2}",
                  originalTime,
                  utcTime,
                  utcTime.Kind);
// The example displays the following output to the console:
//       6/19/2008 7:00:00 AM +05:00 converted to 6/19/2008 2:00:00 AM Utc
Dim originalTime As New DateTimeOffset(#6/19/2008 7:00AM#, _
                                       New TimeSpan(5, 0, 0))
Dim utcTime As Date = originalTime.UtcDateTime
Console.WriteLine("{0} converted to {1} {2}", _
                  originalTime, _
                  utcTime, _
                  utcTime.Kind.ToString())
' The example displays the following output to the console:
'       6/19/2008 7:00:00 AM +05:00 converted to 6/19/2008 2:00:00 AM Utc
转换本地时间
若要指示 DateTimeOffset 值表示本地时间，可以将 DateTimeOffset.DateTime 属性返回的 DateTime 值传递给 static（在 Visual Basic 中为 Shared）SpecifyKind 方法。 该方法将传递给它的日期和时间作为其首个参数返回，但会将 Kind 属性设置为其第二个参数指定的值。 以下代码在转换 DateTimeOffset 值（其偏移量对应于本地时区的偏移量）时使用 SpecifyKind 方法：
DateTime sourceDate = new DateTime(2008, 6, 19, 7, 0, 0);
DateTimeOffset utcTime1 = new DateTimeOffset(sourceDate,
                          TimeZoneInfo.Local.GetUtcOffset(sourceDate));
DateTime utcTime2 = utcTime1.DateTime;
if (utcTime1.Offset.Equals(TimeZoneInfo.Local.GetUtcOffset(utcTime1.DateTime)))
   utcTime2 = DateTime.SpecifyKind(utcTime2, DateTimeKind.Local);
Console.WriteLine("{0} converted to {1} {2}",
                  utcTime1,
                  utcTime2,
                  utcTime2.Kind);
// The example displays the following output to the console:
//   6/19/2008 7:00:00 AM -07:00 converted to 6/19/2008 7:00:00 AM Local
Dim sourceDate As Date = #06/19/2008 7:00AM#
Dim utcTime1 As New DateTimeOffset(sourceDate, _
                                   TimeZoneInfo.Local.GetUtcOffset(sourceDate))
Dim utcTime2 As Date = utcTime1.DateTime
If utcTime1.Offset.Equals(TimeZoneInfo.Local.GetUtcOffset(utcTime1.DateTime)) Then
    utcTime2 = DateTime.SpecifyKind(utcTime2, DateTimeKind.Local)
End If
Console.WriteLine("{0} converted to {1} {2}", _
                  utcTime1, _
                  utcTime2, _
                  utcTime2.Kind.ToString())
' The example displays the following output to the console:
'   6/19/2008 7:00:00 AM -07:00 converted to 6/19/2008 7:00:00 AM Local      
还可以使用 DateTimeOffset.LocalDateTime 属性将 DateTimeOffset 值转换为本地 DateTime 值。 返回的 DateTime 值的 Kind 属性为 Local。 以下代码在转换 DateTimeOffset 值（其偏移量对应于本地时区的偏移量）时使用 DateTimeOffset.LocalDateTime 属性：
DateTime sourceDate = new DateTime(2008, 6, 19, 7, 0, 0);
DateTimeOffset localTime1 = new DateTimeOffset(sourceDate,
                          TimeZoneInfo.Local.GetUtcOffset(sourceDate));
DateTime localTime2 = localTime1.LocalDateTime;
Console.WriteLine("{0} converted to {1} {2}",
                  localTime1,
                  localTime2,
                  localTime2.Kind);
// The example displays the following output to the console:
//   6/19/2008 7:00:00 AM -07:00 converted to 6/19/2008 7:00:00 AM Local
Dim sourceDate As Date = #06/19/2008 7:00AM#
Dim localTime1 As New DateTimeOffset(sourceDate, _
                                   TimeZoneInfo.Local.GetUtcOffset(sourceDate))
Dim localTime2 As Date = localTime1.LocalDateTime
Console.WriteLine("{0} converted to {1} {2}", _
                  localTime1, _
                  localTime2, _
                  localTime2.Kind.ToString())
' The example displays the following output to the console:
'   6/19/2008 7:00:00 AM -07:00 converted to 6/19/2008 7:00:00 AM Local      
使用 DateTimeOffset.LocalDateTime 属性检索 DateTime 值时，该属性的 get 访问器会先将 DateTimeOffset 值转换为 UTC，然后通过调用 ToLocalTime 方法将其转换为本地时间。 此行为意味着，可以从 DateTimeOffset.LocalDateTime 属性检索值，同时执行时区转换和类型转换。 还意味着在执行转换期间应用本地时区的调整规则。 以下代码说明了如何使用 DateTimeOffset.LocalDateTime 属性同时执行类型和时区转换。 示例输出适用于设置为太平洋时区（美国和加拿大）的计算机。 11 月的日期为太平洋标准时间（UTC-8），而 6 月的日期为夏令时（UTC-7）。
DateTimeOffset originalDate;
DateTime localDate;
// Convert time originating in a different time zone
originalDate = new DateTimeOffset(2008, 6, 18, 7, 0, 0,
                                  new TimeSpan(-5, 0, 0));
localDate = originalDate.LocalDateTime;
Console.WriteLine("{0} converted to {1} {2}",
                  originalDate,
                  localDate,
                  localDate.Kind);
// Convert time originating in a different time zone
// so local time zone's adjustment rules are applied
originalDate = new DateTimeOffset(2007, 11, 4, 4, 0, 0,
                                  new TimeSpan(-5, 0, 0));
localDate = originalDate.LocalDateTime;
Console.WriteLine("{0} converted to {1} {2}",
                  originalDate,
                  localDate,
                  localDate.Kind);
// The example displays the following output to the console,
// when you run it on a machine that is set to Pacific Time (US & Canada):
//       6/18/2008 7:00:00 AM -05:00 converted to 6/18/2008 5:00:00 AM Local
//       11/4/2007 4:00:00 AM -05:00 converted to 11/4/2007 1:00:00 AM Local
Dim originalDate As DateTimeOffset
Dim localDate As Date
' Convert time originating in a different time zone
originalDate = New DateTimeOffset(#06/19/2008 7:00AM#, _
                                  New TimeSpan(-5, 0, 0))
localDate = originalDate.LocalDateTime
Console.WriteLine("{0} converted to {1} {2}", _
                  originalDate, _
                  localDate, _
                  localDate.Kind.ToString())
' Convert time originating in a different time zone 
' so local time zone's adjustment rules are applied
originalDate = New DateTimeOffset(#11/04/2007 4:00AM#, _
                                  New TimeSpan(-5, 0, 0))
localDate = originalDate.LocalDateTime
Console.WriteLine("{0} converted to {1} {2}", _
                  originalDate, _
                  localDate, _
                  localDate.Kind.ToString())
' The example displays the following output to the console,
' when you run it on a machine that is set to Pacific Time (US & Canada):
'       6/18/2008 7:00:00 AM -05:00 converted to 6/18/2008 5:00:00 AM Local
'       11/4/2007 4:00:00 AM -05:00 converted to 11/4/2007 1:00:00 AM Local
通用转换方法
以下示例定义名为 ConvertFromDateTimeOffset 的方法，该方法可将 DateTimeOffset 值转换为 DateTime 值。 它可根据其偏移量确定 DateTimeOffset 值是 UTC 时间，还是本地时间或其他时间，并定义返回的日期和时间值相应的 Kind 属性。
static DateTime ConvertFromDateTimeOffset(DateTimeOffset dateTime)
   if (dateTime.Offset.Equals(TimeSpan.Zero))
      return dateTime.UtcDateTime;
   else if (dateTime.Offset.Equals(TimeZoneInfo.Local.GetUtcOffset(dateTime.DateTime)))
      return DateTime.SpecifyKind(dateTime.DateTime, DateTimeKind.Local);
      return dateTime.DateTime;
Function ConvertFromDateTimeOffset(dateTime As DateTimeOffset) As Date
    If dateTime.Offset.Equals(TimeSpan.Zero) Then
        Return dateTime.UtcDateTime
    ElseIf dateTime.Offset.Equals(TimeZoneInfo.Local.GetUtcOffset(dateTime.DateTime))
        Return Date.SpecifyKind(dateTime.DateTime, DateTimeKind.Local)
        Return dateTime.DateTime
    End If
End Function
下面的示例调用 ConvertFromDateTimeOffset 方法来转换 DateTimeOffset 值，这些值表示 UTC 时间、本地时间和美国中部标准时区的时间。
DateTime timeComponent = new DateTime(2008, 6, 19, 7, 0, 0);
DateTime returnedDate;
// Convert UTC time
DateTimeOffset utcTime = new DateTimeOffset(timeComponent, TimeSpan.Zero);
returnedDate = ConvertFromDateTimeOffset(utcTime);
Console.WriteLine("{0} converted to {1} {2}",
                  utcTime,
                  returnedDate,
                  returnedDate.Kind);
// Convert local time
DateTimeOffset localTime = new DateTimeOffset(timeComponent,
                           TimeZoneInfo.Local.GetUtcOffset(timeComponent));
returnedDate = ConvertFromDateTimeOffset(localTime);
Console.WriteLine("{0} converted to {1} {2}",
                  localTime,
                  returnedDate,
                  returnedDate.Kind);
// Convert Central Standard Time
DateTimeOffset cstTime = new DateTimeOffset(timeComponent,
               TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time").GetUtcOffset(timeComponent));
returnedDate = ConvertFromDateTimeOffset(cstTime);
Console.WriteLine("{0} converted to {1} {2}",
                  cstTime,
                  returnedDate,
                  returnedDate.Kind);
// The example displays the following output to the console:
//    6/19/2008 7:00:00 AM +00:00 converted to 6/19/2008 7:00:00 AM Utc
//    6/19/2008 7:00:00 AM -07:00 converted to 6/19/2008 7:00:00 AM Local
//    6/19/2008 7:00:00 AM -05:00 converted to 6/19/2008 7:00:00 AM Unspecified
Dim timeComponent As Date = #06/19/2008 7:00AM#
Dim returnedDate As Date
' Convert UTC time
Dim utcTime As New DateTimeOffset(timeComponent, TimeSpan.Zero)
returnedDate = ConvertFromDateTimeOffset(utcTime)
Console.WriteLine("{0} converted to {1} {2}", _
                  utcTime, _
                  returnedDate, _
                  returnedDate.Kind.ToString())
' Convert local time
Dim localTime As New DateTimeOffset(timeComponent, _
                                    TimeZoneInfo.Local.GetUtcOffset(timeComponent))
returnedDate = ConvertFromDateTimeOffset(localTime)
Console.WriteLine("{0} converted to {1} {2}", _
                  localTime, _
                  returnedDate, _
                  returnedDate.Kind.ToString())
' Convert Central Standard Time
Dim cstTime As New DateTimeOffset(timeComponent, _
               TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time").GetUtcOffset(timeComponent))
returnedDate = ConvertFromDateTimeOffset(cstTime)
Console.WriteLine("{0} converted to {1} {2}", _
                  cstTime, _
                  returnedDate, _
                  returnedDate.Kind.ToString())
' The example displays the following output to the console:
'    6/19/2008 7:00:00 AM +00:00 converted to 6/19/2008 7:00:00 AM Utc
'    6/19/2008 7:00:00 AM -07:00 converted to 6/19/2008 7:00:00 AM Local
'    6/19/2008 7:00:00 AM -05:00 converted to 6/19/2008 7:00:00 AM Unspecified
代码会作出两种假设，根据应用程序及其日期和时间值的来源，这两种假设不一定始终有效：
假定偏移量为 TimeSpan.Zero 的日期和时间值表示 UTC。 事实上，UTC 并不是特定时区中的时间，而是世界时区中的时间相对于它进行标准化的时间。 时区偏移量还可能为 Zero。
假定偏移量等于本地时区偏移量的日期和时间表示本地时区。 由于日期和时间值已从其原始时区解除关联，因此这可能不成立；日期和时间可能源自具有相同偏移量的其他时区。
日期、时间和时区