具現化 DateTimeOffset 物件

發行項
08/21/2008

更新：2007 年 11 月

DateTimeOffset 類別提供許多方法來建立新的 DateTimeOffset 值。其中有許多都是直接對應於具現化新 DateTime 值的方法，經加強後，可讓您指定日期和時間值與 Coordinated Universal Time (UTC) 之間的位移。特別是，您可以利用下列方式具現化 DateTimeOffset 值：

使用日期和時間常值。
呼叫 DateTimeOffset 建構函式。
將值隱含轉換成 DateTimeOffset 值。
剖析日期和時間的字串表示。

本主題將提供更詳細的解說和程式碼範例，來說明這些具現化新 DateTimeOffset 值的方法。

日期和時間常值

對於支援的語言，要具現化 DateTime 值，最常見的其中一種方式就是將日期和時間提供為固定的常值。例如，下列 Visual Basic 程式碼會建立一個 DateTime 物件，其值為 2008 年 1 月 1 日 10:00 AM。

Dim literalDate1 As Date = #05/01/2008 8:06:32 AM#
Console.WriteLine(literalDate1.ToString() )
' Displays:
'              5/1/2008 8:06:32 AM

當您使用支援 DateTime 常值的語言時，也可以使用日期和時間常值具現化 DateTimeOffset 值。例如，下列 Visual Basic 程式碼會建立一個 DateTimeOffset 物件。

Dim literalDate As DateTimeOffset = #05/01/2008 8:06:32 AM#
Console.WriteLine(literalDate.ToString() )
' Displays:
'              5/1/2008 8:06:32 AM -07:00

如主控台輸出所示，以此方式建立的 DateTimeOffset 值會指派成為本地時區的位移。這表示如果程式碼在另一台電腦上執行，使用字元常值指派的 DateTimeOffset 值不會識別單一時間點。

DateTimeOffset 建構函式

DateTimeOffset 型別定義有六個建構函式。其中四個直接對應於 DateTime 建構函式，並有一個型別為 TimeSpan 的額外參數，此參數會定義日期和時間與 UTC 之間的位移。這些建構函式可讓您根據其個別日期和時間元件的值來定義 DateTimeOffset 值。例如，下列程式碼使用這四個建構函式具現化 DateTimeOffset 物件，其值全部都是 7/1/2008 12:05 AM +01:00。

Dim dateAndTime As DateTimeOffset

' Instantiate date and time using years, months, days, 
' hours, minutes, and seconds
dateAndTime = New DateTimeOffset(2008, 5, 1, 8, 6, 32, _
                                 New TimeSpan(1, 0, 0))
Console.WriteLine(dateAndTime)
' Instantiate date and time using years, months, days,
' hours, minutes, seconds, and milliseconds
dateAndTime = New DateTimeOffset(2008, 5, 1, 8, 6, 32, 545, _
                                 New TimeSpan(1, 0, 0))
Console.WriteLine("{0} {1}", dateAndTime.ToString("G"), _
                             dateAndTime.ToString("zzz"))

' Instantiate date and time using Persian calendar with years,
' months, days, hours, minutes, seconds, and milliseconds
dateAndTime = New DateTimeOffset(1387, 2, 12, 8, 6, 32, 545, New PersianCalendar, New TimeSpan(1, 0, 0))
' Note that the console output displays the date in the Gregorian
' calendar, not the Persian calendar. 
Console.WriteLine("{0} {1}", dateAndTime.ToString("G"), _
                             dateAndTime.ToString("zzz"))

' Instantiate date and time using number of ticks
' 05/01/2008 8:06:32 AM is 633,452,259,920,000,000 ticks
dateAndTime = New DateTimeOffset(633452259920000000, New TimeSpan(1, 0, 0))  
Console.WriteLine(dateAndTime)
' The example displays the following output to the console:
'       5/1/2008 8:06:32 AM +01:00
'       5/1/2008 8:06:32 AM +01:00
'       5/1/2008 8:06:32 AM +01:00
'       5/1/2008 8:06:32 AM +01:00

DateTimeOffset dateAndTime;

// Instantiate date and time using years, months, days, 
// hours, minutes, and seconds
dateAndTime = new DateTimeOffset(2008, 5, 1, 8, 6, 32, 
                                 new TimeSpan(1, 0, 0));
Console.WriteLine(dateAndTime);
// Instantiate date and time using years, months, days,
// hours, minutes, seconds, and milliseconds
dateAndTime = new DateTimeOffset(2008, 5, 1, 8, 6, 32, 545, 
                                 new TimeSpan(1, 0, 0));
Console.WriteLine("{0} {1}", dateAndTime.ToString("G"), 
                             dateAndTime.ToString("zzz"));

// Instantiate date and time using Persian calendar with years,
// months, days, hours, minutes, seconds, and milliseconds
dateAndTime = new DateTimeOffset(1387, 2, 12, 8, 6, 32, 545, 
                                 new PersianCalendar(), 
                                 new TimeSpan(1, 0, 0));
// Note that the console output displays the date in the Gregorian
// calendar, not the Persian calendar. 
Console.WriteLine("{0} {1}", dateAndTime.ToString("G"), 
                             dateAndTime.ToString("zzz"));

// Instantiate date and time using number of ticks
// 05/01/2008 8:06:32 AM is 633,452,259,920,000,000 ticks
dateAndTime = new DateTimeOffset(633452259920000000, new TimeSpan(1, 0, 0));  
Console.WriteLine(dateAndTime);
// The example displays the following output to the console:
//       5/1/2008 8:06:32 AM +01:00
//       5/1/2008 8:06:32 AM +01:00
//       5/1/2008 8:06:32 AM +01:00
//       5/1/2008 8:06:32 AM +01:00

請注意，當 DateTimeOffset 物件的值使用 PersianCalendar 物件做為其建構函式的其中一個引數具現化，並顯示在主控台上時，會以西曆表示日期，而不是使用波斯曆表示。若要使用波斯曆輸出日期，請參閱 PersianCalendar 主題中的範例。

另外兩個建構函式則會從 DateTime 值來建立 DateTimeOffset 物件。其中的第一個建構函式有單一參數，這個 DateTime 值會轉換成 DateTimeOffset 值。所產生 DateTimeOffset 值的位移會根據建構函式單一參數的 Kind 屬性而定。如果其值為 DateTimeKind.Utc，位移會設成等於 TimeSpan.Zero。否則，其位移就會設成等於本地時區的位移。下列範例說明如何使用這個建構函式具現化表示 UTC 和本地時區的 DateTimeOffset 物件：

' Declare date; Kind property is DateTimeKind.Unspecified
Dim sourceDate As Date = #5/1/2008 8:30 AM#
Dim targetTime As DateTimeOffset

' Instantiate a DateTimeOffset value from a UTC time 
Dim utcTime As Date = Date.SpecifyKind(sourceDate, DateTimeKind.Utc)
targetTime = New DateTimeOffset(utcTime)
Console.WriteLine(targetTime)
' Displays 5/1/2008 8:30:00 AM +00:00
' Because the Kind property is DateTimeKind.Utc, 
' the offset is TimeSpan.Zero.


' Instantiate a DateTimeOffset value from a local time
Dim localTime As Date = Date.SpecifyKind(sourceDate, DateTimeKind.Local)
targetTime = New DateTimeOffset(localTime)
Console.WriteLine(targetTime)
' Displays 5/1/2008 8:30:00 AM -07:00
' Because the Kind property is DateTimeKind.Local, 
' the offset is that of the local time zone.

' Instantiate a DateTimeOffset value from an unspecified time
targetTime = New DateTimeOffset(sourceDate)
Console.WriteLine(targetTime)
' Displays 5/1/2008 8:30:00 AM -07:00
' Because the Kind property is DateTimeKind.Unspecified, 
' the offset is that of the local time zone.

'

// Declare date; Kind property is DateTimeKind.Unspecified
DateTime sourceDate = new DateTime(2008, 5, 1, 8, 30, 0);
DateTimeOffset targetTime;

// Instantiate a DateTimeOffset value from a UTC time 
DateTime utcTime = DateTime.SpecifyKind(sourceDate, DateTimeKind.Utc);
targetTime = new DateTimeOffset(utcTime);
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM +00:00
// Because the Kind property is DateTimeKind.Utc, 
// the offset is TimeSpan.Zero.

// Instantiate a DateTimeOffset value from a UTC time with a zero offset
targetTime = new DateTimeOffset(utcTime, TimeSpan.Zero);
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM +00:00
// Because the Kind property is DateTimeKind.Utc, 
// the call to the constructor succeeds

// Instantiate a DateTimeOffset value from a UTC time with a negative offset
try
{
   targetTime = new DateTimeOffset(utcTime, new TimeSpan(-2, 0, 0));
   Console.WriteLine(targetTime);
}
catch (ArgumentException)
{
   Console.WriteLine("Attempt to create DateTimeOffset value from {0} failed.", 
                      targetTime);
}   
// Throws exception and displays the following to the console:
//   Attempt to create DateTimeOffset value from 5/1/2008 8:30:00 AM +00:00 failed.

// Instantiate a DateTimeOffset value from a local time
DateTime localTime = DateTime.SpecifyKind(sourceDate, DateTimeKind.Local);
targetTime = new DateTimeOffset(localTime);
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM -07:00
// Because the Kind property is DateTimeKind.Local, 
// the offset is that of the local time zone.

// Instantiate a DateTimeOffset value from an unspecified time
targetTime = new DateTimeOffset(sourceDate);
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM -07:00
// Because the Kind property is DateTimeKind.Unspecified, 
// the offset is that of the local time zone.

注意事項：
呼叫具有單一 DateTime 參數之 DateTimeOffset 建構函式的多載，就等於將 DateTime 值隱含轉換成 DateTimeOffset 值。

第二個建構函式會從 DateTime 值建立 DateTimeOffset 物件，它有兩個參數：一個是要轉換的 DateTime 值，另一個是表示日期和時間與 UTC 之間位移的 TimeSpan 值。此位移值必須對應於建構函式第一個參數的 Kind 屬性，否則會擲回 ArgumentException。如果第一個參數的 Kind 屬性是 DateTimeKind.Utc，則第二個參數的值必須是 TimeSpan.Zero。如果第一個參數的 Kind 屬性是 DateTimeKind.Local，則第二個參數的值必須是本機系統時區的位移。如果第一個參數的 Kind 屬性是 DateTimeKind.Unspecified，則位移可以是任何有效值。下列程式碼顯示這個建構函式的呼叫，以將 DateTime 轉換成 DateTimeOffset 值。

Dim sourceDate As Date = #5/1/2008 8:30 AM#
Dim targetTime As DateTimeOffset

' Instantiate a DateTimeOffset value from a UTC time with a zero offset.
Dim utcTime As Date = Date.SpecifyKind(sourceDate, DateTimeKind.Utc)
targetTime = New DateTimeOffset(utcTime, TimeSpan.Zero)
Console.WriteLine(targetTime)
' Displays 5/1/2008 8:30:00 AM +00:00
' Because the Kind property is DateTimeKind.Utc,  
' the call to the constructor succeeds.

' Instantiate a DateTimeOffset value from a UTC time with a non-zero offset.
Try
   targetTime = New DateTimeOffset(utcTime, New TimeSpan(-2, 0, 0))
   Console.WriteLine(targetTime)
Catch e As ArgumentException
   Console.WriteLine("Attempt to create DateTimeOffset value from {0} failed.", _
                      utcTime)
End Try   
' Throws exception and displays the following to the console:
'   Attempt to create DateTimeOffset value from 5/1/2008 8:30:00 AM failed.

' Instantiate a DateTimeOffset value from a local time with 
' the offset of the local time zone.
Dim localTime As Date = Date.SpecifyKind(sourceDate, DateTimeKind.Local)
targetTime = New DateTimeOffset(localTime, _
                                TimeZoneInfo.Local.GetUtcOffset(localTime))
Console.WriteLine(targetTime)
' Because the Kind property is DateTimeKind.Local and the offset matches
' that of the local time zone, the call to the constructor succeeds.

' Instantiate a DateTimeOffset value from a local time with a zero offset.
Try
   targetTime = New DateTimeOffset(localTime, TimeSpan.Zero)
   Console.WriteLine(targetTime)
Catch e As ArgumentException
   Console.WriteLine("Attempt to create DateTimeOffset value from {0} failed.", _
                      localTime)
End Try   
' Throws exception and displays the following to the console:
'   Attempt to create DateTimeOffset value from 5/1/2008 8:30:00 AM failed.

' Instantiate a DateTimeOffset value with an arbitary time zone. 
Dim timeZoneName As String = "Central Standard Time"
Dim offset As TimeSpan = TimeZoneInfo.FindSystemTimeZoneById(timeZoneName). _
                         GetUtcOffset(sourceDate) 
targetTime = New DateTimeOffset(sourceDate, offset)
Console.WriteLine(targetTime)
' Displays 5/1/2008 8:30:00 AM -05:00

DateTime sourceDate = new DateTime(2008, 5, 1, 8, 30, 0);
DateTimeOffset targetTime;

// Instantiate a DateTimeOffset value from a UTC time with a zero offset.
DateTime utcTime = DateTime.SpecifyKind(sourceDate, DateTimeKind.Utc);
targetTime = new DateTimeOffset(utcTime, TimeSpan.Zero);
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM +00:00
// Because the Kind property is DateTimeKind.Utc,  
// the call to the constructor succeeds

// Instantiate a DateTimeOffset value from a UTC time with a non-zero offset.
try
{
   targetTime = new DateTimeOffset(utcTime, new TimeSpan(-2, 0, 0));
   Console.WriteLine(targetTime);
}
catch (ArgumentException)
{
   Console.WriteLine("Attempt to create DateTimeOffset value from {0} failed.", 
                      utcTime);
}   
// Throws exception and displays the following to the console:
//   Attempt to create DateTimeOffset value from 5/1/2008 8:30:00 AM failed.

// Instantiate a DateTimeOffset value from a local time with 
// the offset of the local time zone
DateTime localTime = DateTime.SpecifyKind(sourceDate, DateTimeKind.Local);
targetTime = new DateTimeOffset(localTime, 
                                TimeZoneInfo.Local.GetUtcOffset(localTime));
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM -07:00
// Because the Kind property is DateTimeKind.Local and the offset matches
// that of the local time zone, the call to the constructor succeeds.

// Instantiate a DateTimeOffset value from a local time with a zero offset.
try
{
   targetTime = new DateTimeOffset(localTime, TimeSpan.Zero);
   Console.WriteLine(targetTime);
}
catch (ArgumentException)
{
   Console.WriteLine("Attempt to create DateTimeOffset value from {0} failed.", 
                      localTime);
}   
// Throws exception and displays the following to the console:
//   Attempt to create DateTimeOffset value from 5/1/2008 8:30:00 AM failed.

// Instantiate a DateTimeOffset value with an arbitary time zone. 
string timeZoneName = "Central Standard Time";
TimeSpan offset = TimeZoneInfo.FindSystemTimeZoneById(timeZoneName). 
                         GetUtcOffset(sourceDate); 
targetTime = new DateTimeOffset(sourceDate, offset);
Console.WriteLine(targetTime);
// Displays 5/1/2008 8:30:00 AM -05:00

隱含型別轉換

DateTimeOffset 型別支援一種隱含型別轉換：從 DateTime 值轉換成 DateTimeOffset 值 (隱含型別轉換是指從某個型別轉換成另一個型別，而無須明確轉換 (C# 為 Cast，Visual Basic 為 Conversion) 且不會遺失資訊)。它可讓您撰寫下列的程式碼。

Dim targetTime As DateTimeOffset

' The Kind property of sourceDate is DateTimeKind.Unspecified
Dim sourceDate As Date = #5/1/2008 8:30 AM#
targetTime = sourceDate
Console.WriteLine(targetTime)   
' Displays 5/1/2008 8:30:00 AM -07:00

' define a UTC time (Kind property is DateTimeKind.Utc)
Dim utcTime As Date = Date.SpecifyKind(sourceDate, DateTimeKind.Utc)
targetTime = utcTime
Console.WriteLine(targetTime)   
' Displays 5/1/2008 8:30:00 AM +00:00

' Define a local time (Kind property is DateTimeKind.Local)
Dim localTime As Date = Date.SpecifyKind(sourceDate, DateTimeKind.Local)
targetTime = localTime
Console.WriteLine(targetTime)      
' Displays 5/1/2008 8:30:00 AM -07:00

DateTimeOffset targetTime;

// The Kind property of sourceDate is DateTimeKind.Unspecified
DateTime sourceDate = new DateTime(2008, 5, 1, 8, 30, 0);
targetTime = sourceDate;
Console.WriteLine(targetTime);   
// Displays 5/1/2008 8:30:00 AM -07:00

// define a UTC time (Kind property is DateTimeKind.Utc)
DateTime utcTime = DateTime.SpecifyKind(sourceDate, DateTimeKind.Utc);
targetTime = utcTime;
Console.WriteLine(targetTime);   
// Displays 5/1/2008 8:30:00 AM +00:00

// Define a local time (Kind property is DateTimeKind.Local)
DateTime localTime = DateTime.SpecifyKind(sourceDate, DateTimeKind.Local);
targetTime = localTime;
Console.WriteLine(targetTime);      
// Displays 5/1/2008 8:30:00 AM -07:00

所產生 DateTimeOffset 值的位移會根據 DateTime.Kind 屬性值而定。如果其值為 DateTimeKind.Utc，位移會設成等於 TimeSpan.Zero。如果其值為 DateTimeKind.Local 或 DateTimeKind.Unspecified，位移就會設成等於本地時區的位移。

剖析日期和時間的字串表示

DateTimeOffset 型別支援四種方法，可將日期和時間的字串表示轉換成 DateTimeOffset 值：

Parse，此方法會嘗試將日期和時間的字串表示轉換成 DateTimeOffset 值，如果轉換失敗，會擲出例外狀況。
TryParse，此方法會嘗試將日期和時間的字串表示轉換成 DateTimeOffset 值，如果轉換失敗，會傳回 false。
ParseExact，此方法會嘗試將指定格式的日期和時間字串表示轉換成 DateTimeOffset 值。如果轉換失敗，此方法會擲回例外狀況。
TryParseExact，此方法會嘗試將指定格式的日期和時間字串表示轉換成 DateTimeOffset 值。如果轉換失敗，此方法會傳回 false。

下列範例顯示這四個字串轉換方法的呼叫，以具現化 DateTimeOffset 值。

Dim timeString As String 
Dim targetTime As DateTimeOffset

timeString = "05/01/2008 8:30 AM +01:00"
Try
   targetTime = DateTimeOffset.Parse(timeString)
   Console.WriteLine(targetTime)
Catch e As FormatException
   Console.WriteLine("Unable to parse {0}.", timeString)   
End Try   

timeString = "05/01/2008 8:30 AM"
If DateTimeOffset.TryParse(timeString, targetTime) Then
   Console.WriteLine(targetTime)
Else
   Console.WriteLine("Unable to parse {0}.", timeString)   
End If

timeString = "Thursday, 01 May 2008 08:30"
Try
   targetTime = DateTimeOffset.ParseExact(timeString, "f", _
                CultureInfo.InvariantCulture)
   Console.WriteLine(targetTime)
Catch e As FormatException
   Console.WriteLine("Unable to parse {0}.", timeString)   
End Try   

timeString = "Thursday, 01 May 2008 08:30 +02:00"
Dim formatString As String 
formatString = CultureInfo.InvariantCulture.DateTimeFormat.LongDatePattern & _
                " " & _
                CultureInfo.InvariantCulture.DateTimeFormat.ShortTimePattern & _
                " zzz" 
If DateTimeOffset.TryParseExact(timeString, _
                                formatString, _
                                CultureInfo.InvariantCulture, _
                                DateTimeStyles.AllowLeadingWhite, _
                                targetTime) Then
   Console.WriteLine(targetTime)
Else
   Console.WriteLine("Unable to parse {0}.", timeString)
End If      
' The example displays the following output to the console:
'    5/1/2008 8:30:00 AM +01:00
'    5/1/2008 8:30:00 AM -07:00
'    5/1/2008 8:30:00 AM -07:00
'    5/1/2008 8:30:00 AM +02:00

string timeString; 
DateTimeOffset targetTime;

timeString = "05/01/2008 8:30 AM +01:00";
try
{
   targetTime = DateTimeOffset.Parse(timeString);
   Console.WriteLine(targetTime);
}
catch (FormatException)
{
   Console.WriteLine("Unable to parse {0}.", timeString);   
}   

timeString = "05/01/2008 8:30 AM";
if (DateTimeOffset.TryParse(timeString, out targetTime))
   Console.WriteLine(targetTime);
else
   Console.WriteLine("Unable to parse {0}.", timeString);   

timeString = "Thursday, 01 May 2008 08:30";
try
{
   targetTime = DateTimeOffset.ParseExact(timeString, "f", 
                CultureInfo.InvariantCulture);
   Console.WriteLine(targetTime);
}
catch (FormatException)
{
   Console.WriteLine("Unable to parse {0}.", timeString);   
}   

timeString = "Thursday, 01 May 2008 08:30 +02:00";
string formatString; 
formatString = CultureInfo.InvariantCulture.DateTimeFormat.LongDatePattern +
                " " +
                CultureInfo.InvariantCulture.DateTimeFormat.ShortTimePattern +
                " zzz"; 
if (DateTimeOffset.TryParseExact(timeString, 
                                formatString, 
                                CultureInfo.InvariantCulture, 
                                DateTimeStyles.AllowLeadingWhite, 
                                out targetTime))
   Console.WriteLine(targetTime);
else
   Console.WriteLine("Unable to parse {0}.", timeString);
// The example displays the following output to the console:
//    5/1/2008 8:30:00 AM +01:00
//    5/1/2008 8:30:00 AM -07:00
//    5/1/2008 8:30:00 AM -07:00
//    5/1/2008 8:30:00 AM +02:00

請參閱

其他資源

時間和時區

共用方式為

具現化 DateTimeOffset 物件

日期和時間常值

DateTimeOffset 建構函式

隱含型別轉換

剖析日期和時間的字串表示

請參閱

其他資源

其他資源