Articolo
11/18/2011

DateTime.FromFileTime Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Converts the specified Windows file time to an equivalent local time.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Shared Function FromFileTime ( _
    fileTime As Long _
) As DateTime

public static DateTime FromFileTime(
    long fileTime
)

Parameters

fileTime
Type: System.Int64
A Windows file time expressed in ticks.

Return Value

Type: System.DateTime
An object that represents a local time that is equivalent to the date and time represented by the fileTime parameter.

Exceptions

Exception	Condition
ArgumentOutOfRangeException	fileTime is less than 0 or represents a time greater than MaxValue.

Remarks

A Windows file time is a 64-bit value that represents the number of 100-nanosecond intervals that have elapsed since 12:00 midnight, January 1, 1601 A.D. (C.E.) Coordinated Universal Time (UTC). Windows uses a file time to record when an application creates, accesses, or writes to a file.

The fileTime parameter specifies a file time expressed in 100-nanosecond ticks.

The return value is a DateTime whose Kind property is DateTimeKind.Local.

Notes to Callers

Ordinarily, the FromFileTime method restores a DateTime value that was saved by the ToFileTime method. However, the two values may differ under the following conditions:

If the serialization and deserialization of the DateTime value occur in different time zones. For example, if a DateTime value with a time of 12:30 P.M. in the U.S. Eastern Time zone is serialized, and then deserialized in the U.S. Pacific Time zone, the original value of 12:30 PM is adjusted to 9:30 A.M. to reflect the difference between the two time zones.

If the DateTime value that is serialized represents an invalid time in the local time zone. In this case, the ToFileTime method adjusts the restored DateTime value so that it represents a valid time in the local time zone.

For example, the transition from standard time to daylight saving time occurs in the U.S. Pacific Time zone on March 14, 2010, at 2:00 A.M., when the time advances by one hour, to 3:00 A.M. This hour interval is an invalid time, that is, a time interval that does not exist in this time zone. The following example shows that when a time that falls within this range is converted to a long integer value by the ToFileTime method and is then restored by the FromFileTime method, the original value is adjusted to become a valid time. You can determine whether a particular date and time value may be subject to modification by passing it to the TimeZoneInfo.IsInvalidTime method, as the example illustrates.

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim date1 As New DateTime(2010, 3, 14, 2, 30, 0)
      outputBlock.Text += String.Format("Invalid Time: {0}", TimeZoneInfo.Local.IsInvalidTime(date1)) & vbCrLf
      Dim ft As Long = date1.ToFileTime()
      Dim date2 As DateTime = DateTime.FromFileTime(ft)
      outputBlock.Text += String.Format("{0} -> {1}", date1, date2) & vbCrLf
   End Sub
End Module
' The example displays the following output:
'       Invalid Time: True
'       3/14/2010 2:30:00 AM -> 3/14/2010 3:30:00 AM

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      DateTime date1 = new DateTime(2010, 3, 14, 2, 30, 00);
      outputBlock.Text += String.Format("Invalid Time: {0}",
                        TimeZoneInfo.Local.IsInvalidTime(date1)) + "\n";
      long ft = date1.ToFileTime();
      DateTime date2 = DateTime.FromFileTime(ft);
      outputBlock.Text += String.Format("{0} -> {1}", date1, date2) + "\n";
   }
}
// The example displays the following output:
//       Invalid Time: True
//       3/14/2010 2:30:00 AM -> 3/14/2010 3:30:00 AM

Examples

The following example demonstrates the FromFileTime method.

Public Function FileAge(ByVal fileCreationTime As Long) As System.TimeSpan
   Dim now As System.DateTime
   now = System.DateTime.Now

   Try
      Dim fCreationTime As System.DateTime
      Dim fAge As System.TimeSpan
      fCreationTime = System.DateTime.FromFileTime(fileCreationTime)
      fAge = now.Subtract(fCreationTime)
      Return fAge
   Catch exp As ArgumentOutOfRangeException
      ' fileCreationTime is not valid, so re-throw the exception.
      Throw
   End Try
End Function

public System.TimeSpan FileAge(long fileCreationTime)
{

   System.DateTime now = System.DateTime.Now;
   try
   {
      System.DateTime fCreationTime =
         System.DateTime.FromFileTime(fileCreationTime);
      System.TimeSpan fileAge = now.Subtract(fCreationTime);
      return fileAge;
   }
   catch (ArgumentOutOfRangeException)
   {
      // fileCreationTime is not valid, so re-throw the exception.
      throw;
   }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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