SafeFileHandle Class
Represents a wrapper class for a file handle.
Assembly: mscorlib (in mscorlib.dll)
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 AndAlso 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
- SecurityPermission
for permission to call unmanaged code. Security action: LinkDemand. Associated enumeration: SecurityPermissionFlag.UnmanagedCode
System.Runtime.ConstrainedExecution.CriticalFinalizerObject
System.Runtime.InteropServices.SafeHandle
Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
Microsoft.Win32.SafeHandles.SafeFileHandle
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.