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如何:在日期和时间算术中使用时区
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。
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。
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。