IDisposable.Dispose-Methode
Führt anwendungsspezifische Aufgaben durch, die mit der Freigabe, der Zurückgabe oder dem Zurücksetzen von nicht verwalteten Ressourcen zusammenhängen.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Sub Dispose
'Usage
Dim instance As IDisposable
instance.Dispose
void Dispose ()
void Dispose ()
void Dispose ()
function Dispose ()
Hinweise
Mit dieser Methode werden nicht verwaltete Ressourcen wie Dateien, Streams und Handles, die für eine Instanz der diese Schnittstelle implementierenden Klasse reserviert sind, geschlossen oder freigegeben. Diese Methode wird als Konvention für alle Aufgaben verwendet, die mit der Freigabe der für ein Objekt reservierten Ressourcen oder mit der Vorbereitung der Wiederverwendung eines Objekts zusammenhängen.
Wichtig
C++-Programmierer sollten Destructors and Finalizers in Visual C++ lesen. In .NET Framework, Version 2.0, unterstützt der C++-Compiler das Implementieren der deterministischen Freigabe von Ressourcen und verhindert das direkte Implementieren der Dispose-Methode.
Stellen Sie bei Implementierung dieser Methode sicher, dass alle reservierten Ressourcen freigegeben werden, indem der Aufruf durch die Kapselungshierarchie weitergeleitet wird. Wenn ein Objekt A z. B. ein Objekt B reserviert und Objekt B ein Objekt C, muss die Dispose-Implementierung von A Dispose für B aufrufen, und diese muss wiederum Dispose für C aufrufen. Objekte müssen außerdem die Dispose-Methode ihrer Basisklasse aufrufen, wenn die Basisklasse IDisposable implementiert.
Wenn die Dispose-Methode eines Objekts mehrfach aufgerufen wird, muss das Objekt alle auf den ersten Aufruf folgenden Aufrufe ignorieren. Das Objekt darf keine Ausnahme auslösen, wenn seine Dispose-Methode mehrmals aufgerufen wird. Andere Instanzmethoden als Dispose können eine ObjectDisposedException auslösen, wenn Ressourcen bereits verworfen wurden.
Möglicherweise erwarten die Benutzer, dass ein Ressourcentyp eine bestimmte Vereinbarung zur Unterscheidung zwischen einer zugeordneten und einer freigegebenen Ressource verwendet. Ein Beispiel hierfür sind Streamklassen, von denen traditionell als geöffnet oder geschlossen gesprochen wird. Wenn eine Klasse mit einer derartigen Vereinbarung implementiert wird, kann auch eine öffentliche Methode mit einem benutzerdefinierten Namen (z. B. Schließen) implementiert werden, um die Dispose-Methode aufzurufen.
Da die Dispose-Methode explizit aufgerufen werden muss, müssen Objekte, die IDisposable implementieren, auch einen Finalizer implementieren, der die Freigabe der Ressourcen übernimmt, wenn Dispose nicht aufgerufen wird. In der Standardeinstellung ruft der Garbage Collector vor der Rückgabe des Speichers für ein Objekt dessen Finalizer auf. Nach dem Aufruf der Dispose-Methode ist es allerdings i. d. R. überflüssig, dass der Garbage Collector zusätzlich den Finalizer des freigegebenen Objekts aufruft. Implementierungen von Dispose können die GC.SuppressFinalize-Methode aufrufen, um die automatische Finalisierung zu verhindern.
Weitere Informationen zum Implementieren der Finalizer und der Dispose-Methode finden Sie in der GC-Klasse, in der Object.Finalize-Methode und unter Implementieren der Methoden "Finalize" und "Dispose" zum Bereinigen von nicht verwalteten Ressourcen.
Beispiel
Imports System
Imports System.ComponentModel
' The following example demonstrates how to create
' a resource class that implements the IDisposable interface
' and the IDisposable.Dispose method.
Public Class DisposeExample
' A class that implements IDisposable.
' By implementing IDisposable, you are announcing that
' instances of this type allocate scarce resources.
Public Class MyResource
Implements IDisposable
' Pointer to an external unmanaged resource.
Private handle As IntPtr
' Other managed resource this class uses.
Private component As component
' Track whether Dispose has been called.
Private disposed As Boolean = False
' The class constructor.
Public Sub New(ByVal handle As IntPtr)
Me.handle = handle
End Sub
' Implement IDisposable.
' Do not make this method virtual.
' A derived class should not be able to override this method.
Public Overloads Sub Dispose() Implements IDisposable.Dispose
Dispose(True)
' This object will be cleaned up by the Dispose method.
' Therefore, you should call GC.SupressFinalize to
' take this object off the finalization queue
' and prevent finalization code for this object
' from executing a second time.
GC.SuppressFinalize(Me)
End Sub
' Dispose(bool disposing) executes in two distinct scenarios.
' If disposing equals true, the method has been called directly
' or indirectly by a user's code. Managed and unmanaged resources
' can be disposed.
' If disposing equals false, the method has been called by the
' runtime from inside the finalizer and you should not reference
' other objects. Only unmanaged resources can be disposed.
Private Overloads Sub Dispose(ByVal disposing As Boolean)
' Check to see if Dispose has already been called.
If Not Me.disposed Then
' If disposing equals true, dispose all managed
' and unmanaged resources.
If disposing Then
' Dispose managed resources.
component.Dispose()
End If
' Call the appropriate methods to clean up
' unmanaged resources here.
' If disposing is false,
' only the following code is executed.
CloseHandle(handle)
handle = IntPtr.Zero
End If
disposed = True
End Sub
' Use interop to call the method necessary
' to clean up the unmanaged resource.
<System.Runtime.InteropServices.DllImport("Kernel32")> _
Private Shared Function CloseHandle(ByVal handle As IntPtr) As [Boolean]
End Function
' This finalizer will run only if the Dispose method
' does not get called.
' It gives your base class the opportunity to finalize.
' Do not provide finalize methods in types derived from this class.
Protected Overrides Sub Finalize()
' Do not re-create Dispose clean-up code here.
' Calling Dispose(false) is optimal in terms of
' readability and maintainability.
Dispose(False)
MyBase.Finalize()
End Sub
End Class
Public Shared Sub Main()
' Insert code here to create
' and use the MyResource object.
End Sub
End Class
using System;
using System.ComponentModel;
// The following example demonstrates how to create
// a resource class that implements the IDisposable interface
// and the IDisposable.Dispose method.
public class DisposeExample
{
// A base class that implements IDisposable.
// By implementing IDisposable, you are announcing that
// instances of this type allocate scarce resources.
public class MyResource: IDisposable
{
// Pointer to an external unmanaged resource.
private IntPtr handle;
// Other managed resource this class uses.
private Component component = new Component();
// Track whether Dispose has been called.
private bool disposed = false;
// The class constructor.
public MyResource(IntPtr handle)
{
this.handle = handle;
}
// Implement IDisposable.
// Do not make this method virtual.
// A derived class should not be able to override this method.
public void Dispose()
{
Dispose(true);
// This object will be cleaned up by the Dispose method.
// Therefore, you should call GC.SupressFinalize to
// take this object off the finalization queue
// and prevent finalization code for this object
// from executing a second time.
GC.SuppressFinalize(this);
}
// Dispose(bool disposing) executes in two distinct scenarios.
// If disposing equals true, the method has been called directly
// or indirectly by a user's code. Managed and unmanaged resources
// can be disposed.
// If disposing equals false, the method has been called by the
// runtime from inside the finalizer and you should not reference
// other objects. Only unmanaged resources can be disposed.
private void Dispose(bool disposing)
{
// Check to see if Dispose has already been called.
if(!this.disposed)
{
// If disposing equals true, dispose all managed
// and unmanaged resources.
if(disposing)
{
// Dispose managed resources.
component.Dispose();
}
// Call the appropriate methods to clean up
// unmanaged resources here.
// If disposing is false,
// only the following code is executed.
CloseHandle(handle);
handle = IntPtr.Zero;
}
disposed = true;
}
// Use interop to call the method necessary
// to clean up the unmanaged resource.
[System.Runtime.InteropServices.DllImport("Kernel32")]
private extern static Boolean CloseHandle(IntPtr handle);
// Use C# destructor syntax for finalization code.
// This destructor will run only if the Dispose method
// does not get called.
// It gives your base class the opportunity to finalize.
// Do not provide destructors in types derived from this class.
~MyResource()
{
// Do not re-create Dispose clean-up code here.
// Calling Dispose(false) is optimal in terms of
// readability and maintainability.
Dispose(false);
}
}
public static void Main()
{
// Insert code here to create
// and use the MyResource object.
}
}
#using <System.dll>
#using <System.Windows.Forms.dll>
using namespace System;
using namespace System::ComponentModel;
using namespace System::Windows::Forms;
// The following example demonstrates how to create a class that
// implements the IDisposable interface and the IDisposable.Dispose
// method with finalization to clean up unmanaged resources.
//
public ref class MyResource: public IDisposable
{
private:
// Pointer to an external unmanaged resource.
IntPtr handle;
// A managed resource this class uses.
Component^ component;
// Track whether Dispose has been called.
bool disposed;
public:
// The class constructor.
MyResource( IntPtr handle, Component^ component )
{
this->handle = handle;
this->component = component;
disposed = false;
}
// This method is called if the user explicitly disposes of the
// object (by calling the Dispose method in other managed languages,
// or the destructor in C++). The compiler emits as a call to
// GC::SuppressFinalize( this ) for you, so there is no need to
// call it here.
~MyResource()
{
// Dispose of managed resources.
component->~Component();
// Call C++ finalizer to clean up unmanaged resources.
this->!MyResource();
// Mark the class as disposed. This flag allows you to throw an
// exception if a disposed object is accessed.
disposed = true;
}
// Use interop to call the method necessary to clean up the
// unmanaged resource.
//
[System::Runtime::InteropServices::DllImport("Kernel32")]
static Boolean CloseHandle( IntPtr handle );
// The C++ finalizer destructor ensures that unmanaged resources get
// released if the user releases the object without explicitly
// disposing of it.
//
!MyResource()
{
// Call the appropriate methods to clean up unmanaged
// resources here. If disposing is false when Dispose(bool,
// disposing) is called, only the following code is executed.
CloseHandle( handle );
handle = IntPtr::Zero;
}
};
void main()
{
// Insert code here to create and use the MyResource object.
MyResource^ mr = gcnew MyResource((IntPtr) 42, (Component^) gcnew Button());
mr->~MyResource();
}
import System.*;
import System.ComponentModel.*;
// The following example demonstrates how to create
// a resource class that implements the IDisposable interface
// and the IDisposable.Dispose method.
public class DisposeExample
{
// A base class that implements IDisposable.
// By implementing IDisposable, you are announcing that
// instances of this type allocate scarce resources.
public static class MyResource implements IDisposable
{
// Pointer to an external unmanaged resource.
private IntPtr handle;
// Other managed resource this class uses.
private Component component = new Component();
// Track whether Dispose has been called.
private boolean disposed = false;
// The class constructor.
public MyResource(IntPtr handle)
{
this.handle = handle;
} //MyResource
// Implement IDisposable.
// Do not make this method virtual.
// A derived class should not be able to override this method.
public void Dispose()
{
Dispose(true);
// This object will be cleaned up by the Dispose method.
// Therefore, you should call GC.SupressFinalize to
// take this object off the finalization queue
// and prevent finalization code for this object
// from executing a second time.
GC.SuppressFinalize(this);
} //Dispose
// Dispose(bool disposing) executes in two distinct scenarios.
// If disposing equals true, the method has been called directly
// or indirectly by a user's code. Managed and unmanaged resources
// can be disposed.
// If disposing equals false, the method has been called by the
// runtime from inside the finalizer and you should not reference
// other objects. Only unmanaged resources can be disposed.
private void Dispose(boolean disposing)
{
// Check to see if Dispose has already been called.
if (!(this.disposed)) {
// If disposing equals true, dispose all managed
// and unmanaged resources.
if ( disposing ) {
// Dispose managed resources.
component.Dispose();
}
// Call the appropriate methods to clean up
// unmanaged resources here.
// If disposing is false,
// only the following code is executed.
CloseHandle(handle);
handle = IntPtr.Zero;
}
disposed = true;
} //Dispose
// Use interop to call the method necessary
// to clean up the unmanaged resource.
/** @attribute System.Runtime.InteropServices.DllImport("Kernel32")
*/
private static native Boolean CloseHandle(IntPtr handle);
// Use J# destructor syntax for finalization code.
// This destructor will run only if the Dispose method
// does not get called.
// It gives your base class the opportunity to finalize.
// Do not provide destructors in types derived from this class.
public void finalize()
{
// Do not re-create Dispose clean-up code here.
// Calling Dispose(false) is optimal in terms of
// readability and maintainability.
Dispose(false);
try {
super.finalize();
}
catch(System.Exception e ) {
}
} //finalize
} //MyResource
public static void main(String[] args)
{
// Insert code here to create
// and use the MyResource object.
} //main
} //DisposeExample
Plattformen
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.
Versionsinformationen
.NET Framework
Unterstützt in: 2.0, 1.1, 1.0
.NET Compact Framework
Unterstützt in: 2.0, 1.0
Siehe auch
Referenz
IDisposable-Schnittstelle
IDisposable-Member
System-Namespace