SafeFileHandle Class
Represents a wrapper class for a file handle.
Assembly: mscorlib (in mscorlib.dll)
System.Runtime.ConstrainedExecution.CriticalFinalizerObject
System.Runtime.InteropServices.SafeHandle
Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
Microsoft.Win32.SafeHandles.SafeFileHandle
| Name | Description | |
|---|---|---|
![]() | SafeFileHandle(IntPtr, Boolean) | Initializes a new instance of the SafeFileHandle class. |
| Name | Description | |
|---|---|---|
![]() | IsClosed | Gets a value indicating whether the handle is closed.(Inherited from SafeHandle.) |
![]() | IsInvalid | Gets a value that indicates whether the handle is invalid.(Inherited from SafeHandleZeroOrMinusOneIsInvalid.) |
| Name | Description | |
|---|---|---|
![]() | Close() | Marks the handle for releasing and freeing resources.(Inherited from SafeHandle.) |
![]() | DangerousAddRef(Boolean) | Manually increments the reference counter on SafeHandle instances.(Inherited from SafeHandle.) |
![]() | DangerousGetHandle() | Returns the value of the handle field.(Inherited from SafeHandle.) |
![]() | DangerousRelease() | Manually decrements the reference counter on a SafeHandle instance.(Inherited from SafeHandle.) |
![]() | Dispose() | Releases all resources used by the SafeHandle class.(Inherited from SafeHandle.) |
![]() | Equals(Object) | Determines whether the specified object is equal to the current object.(Inherited from Object.) |
![]() | GetHashCode() | Serves as the default hash function. (Inherited from Object.) |
![]() | GetType() | |
![]() | SetHandleAsInvalid() | Marks a handle as no longer used.(Inherited from SafeHandle.) |
![]() | ToString() | 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.
Important |
|---|
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
requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.
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.


