SafeFileHandle Class

 

Represents a wrapper class for a file handle.

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


<SecurityCriticalAttribute>
Public NotInheritable Class SafeFileHandle
	Inherits SafeHandleZeroOrMinusOneIsInvalid

NameDescription
System_CAPS_pubmethodSafeFileHandle(IntPtr, Boolean)

Initializes a new instance of the SafeFileHandle class.

NameDescription
System_CAPS_pubpropertyIsClosed

Gets a value indicating whether the handle is closed.(Inherited from SafeHandle.)

System_CAPS_pubpropertyIsInvalid

Gets a value that indicates whether the handle is invalid.(Inherited from SafeHandleZeroOrMinusOneIsInvalid.)

NameDescription
System_CAPS_pubmethodClose()

Marks the handle for releasing and freeing resources.(Inherited from SafeHandle.)

System_CAPS_pubmethodDangerousAddRef(Boolean)

Manually increments the reference counter on SafeHandle instances.(Inherited from SafeHandle.)

System_CAPS_pubmethodDangerousGetHandle()

Returns the value of the handle field.(Inherited from SafeHandle.)

System_CAPS_pubmethodDangerousRelease()

Manually decrements the reference counter on a SafeHandle instance.(Inherited from SafeHandle.)

System_CAPS_pubmethodDispose()

Releases all resources used by the SafeHandle class.(Inherited from SafeHandle.)

System_CAPS_pubmethodEquals(Object)

Determines whether the specified object is equal to the current object.(Inherited from Object.)

System_CAPS_pubmethodGetHashCode()

Serves as the default hash function. (Inherited from Object.)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_pubmethodSetHandleAsInvalid()

Marks a handle as no longer used.(Inherited from SafeHandle.)

System_CAPS_pubmethodToString()

Returns a string that represents the current object.(Inherited from Object.)

This class is derived from SafeHandleZeroOrMinusOneIsInvalid. A value of 0 or -1 is an invalid file handle.

System_CAPS_importantImportant

This type implements the IDisposable interface. When you have finished using the type, you should dispose of it either directly or indirectly. To dispose of the type directly, call its Dispose method in a try/catch block. To dispose of it indirectly, use a language construct such as using (in C#) or Using (in Visual Basic). For more information, see the “Using an Object that Implements IDisposable” section in the IDisposable interface topic.

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

SecurityCriticalAttribute

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

Universal Windows Platform
Available since 10
.NET Framework
Available since 2.0

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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