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SafeFileHandle Class

Represents a wrapper class for a file handle.

Namespace:  Microsoft.Win32.SafeHandles
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public NotInheritable Class SafeFileHandle _
	Inherits SafeHandleZeroOrMinusOneIsInvalid

The SafeFileHandle type exposes the following members.

  NameDescription
Public methodSafeFileHandleInitializes a new instance of the SafeFileHandle class.
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  NameDescription
Public propertyIsClosedGets a value indicating whether the handle is closed. (Inherited from SafeHandle.)
Public propertyIsInvalidGets a value that indicates whether the handle is invalid. (Inherited from SafeHandleZeroOrMinusOneIsInvalid.)
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  NameDescription
Public methodCloseMarks the handle for releasing and freeing resources. (Inherited from SafeHandle.)
Public methodDangerousAddRefManually increments the reference counter on SafeHandle instances. (Inherited from SafeHandle.)
Public methodDangerousGetHandleReturns the value of the handle field. (Inherited from SafeHandle.)
Public methodDangerousReleaseManually decrements the reference counter on a SafeHandle instance. (Inherited from SafeHandle.)
Public methodDisposeReleases all resources used by the SafeHandle class. (Inherited from SafeHandle.)
Protected methodDispose(Boolean)Releases the unmanaged resources used by the SafeHandle class specifying whether to perform a normal dispose operation. (Inherited from SafeHandle.)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeFrees all resources associated with the handle. (Inherited from SafeHandle.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodReleaseHandleWhen overridden in a derived class, executes the code required to free the handle. (Inherited from SafeHandle.)
Protected methodSetHandleSets the handle to the specified pre-existing handle. (Inherited from SafeHandle.)
Public methodSetHandleAsInvalidMarks a handle as no longer used. (Inherited from SafeHandle.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Protected fieldhandleSpecifies the handle to be wrapped. (Inherited from SafeHandle.)
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This class is derived from SafeHandleZeroOrMinusOneIsInvalid. A value of 0 or -1 is an invalid file handle.

The following code example demonstrates how to open a file using the SafeFileHandle class and the unmanaged CreateFile function.


Imports System
Imports Microsoft.Win32.SafeHandles
Imports System.Runtime.InteropServices
Imports System.ComponentModel



Module SafeHandlesExample

    Sub Main()
        Try

            Dim loader As New UnmanagedFileLoader("example.xml")


        Catch e As Exception
            Console.WriteLine(e)
        End Try
        Console.ReadLine()

    End Sub
End Module



Class UnmanagedFileLoader


    Public Const FILE_ATTRIBUTE_NORMAL As Short = &H80
    Public Const INVALID_HANDLE_VALUE As Short = -1
    Public Const GENERIC_READ As Long = &H80000000
    Public Const GENERIC_WRITE As UInteger = &H40000000
    Public Const CREATE_NEW As UInteger = 1
    Public Const CREATE_ALWAYS As UInteger = 2
    Public Const OPEN_EXISTING As UInteger = 3


    ' Use interop to call the CreateFile function.
    ' For more information about CreateFile,
    ' see the unmanaged MSDN reference library.
    <DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)> _
    Private Shared Function CreateFile(ByVal lpFileName As String, ByVal dwDesiredAccess As System.UInt32, ByVal dwShareMode As System.UInt32, ByVal lpSecurityAttributes As IntPtr, ByVal dwCreationDisposition As System.UInt32, ByVal dwFlagsAndAttributes As System.UInt32, ByVal hTemplateFile As IntPtr) As Microsoft.Win32.SafeHandles.SafeFileHandle

    End Function


    Private handleValue As Microsoft.Win32.SafeHandles.SafeFileHandle = Nothing



    Public Sub New(ByVal Path As String)
        Load(Path)

    End Sub


    Public Sub Load(ByVal Path As String)
        If Path Is Nothing OrElse Path.Length = 0 Then
            Throw New ArgumentNullException("Path")
        End If

        ' Try to open the file.
        handleValue = CreateFile(Path, GENERIC_WRITE, 0, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero)

        ' If the handle is invalid,
        ' get the last Win32 error 
        ' and throw a Win32Exception.
        If handleValue.IsInvalid Then
            Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error())
        End If

    End Sub


    Public ReadOnly Property Handle() As Microsoft.Win32.SafeHandles.SafeFileHandle
        Get
            ' If the handle is valid,
            ' return it.
            If Not handleValue.IsInvalid Then
                Return handleValue
            Else
                Return Nothing
            End If
        End Get
    End Property
End Class


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

  • SecurityCriticalAttribute 

    requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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