IDisposable.Dispose Methode

Definition

Führt anwendungsspezifische Aufgaben durch, die mit der Freigabe, der Zurückgabe oder dem Zurücksetzen von nicht verwalteten Ressourcen zusammenhängen.Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.

public:
 void Dispose();
public void Dispose ();
abstract member Dispose : unit -> unit
Public Sub Dispose ()

Beispiele

Im folgenden Beispiel wird gezeigt, wie Sie die Dispose-Methode implementieren können.The following example shows how you can implement the Dispose method.

#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();
}
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.
        protected virtual 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;

                // Note disposing has been done.
                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.
    }
}
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.
      Protected Overridable 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

            ' Note disposing has been done.
            disposed = True

         End If
      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

Hinweise

Verwenden Sie diese Methode, um nicht verwaltete Ressourcen, z. b. Dateien, Streams und Handles, die von einer Instanz der-Klasse, die diese Schnittstelle implementiert, zu schließen oder freizugeben.Use this method to close or release unmanaged resources such as files, streams, and handles held by an instance of the class that implements this interface. Gemäß der Konvention wird diese Methode für alle Aufgaben verwendet, die mit der Freigabe von Ressourcen in einem Objekt oder dem Vorbereiten eines Objekts für die Wiederverwendung in Zusammenhang stehen.By convention, this method is used for all tasks associated with freeing resources held by an object, or preparing an object for reuse.

Warnung

Wenn Sie eine Klasse verwenden, die die IDisposable-Schnittstelle implementiert, sollten Sie Ihre Dispose-Implementierung aufzurufen, wenn Sie die Verwendung der-Klasse abgeschlossen haben.If you are using a class that implements the IDisposable interface, you should call its Dispose implementation when you are finished using the class. Weitere Informationen finden Sie im Abschnitt "Verwenden eines Objekts, das iverwerfimplementiert" im IDisposable Thema.For more information, see the "Using an object that implements IDisposable" section in the IDisposable topic.

Wenn Sie diese Methode implementieren, stellen Sie sicher, dass alle gehaltenen Ressourcen freigegeben werden, indem Sie den-Befehl über die Kapselungs HierarchieWhen implementing this method, ensure that all held resources are freed by propagating the call through the containment hierarchy. Wenn ein Objekt a z. b. ein Objekt b zuordnet und Objekt b ein Objekt C zuordnet, muss die Dispose-Implementierung von a Dispose auf B abrufen, das wiederum Dispose in C aufgerufen werden muss.For example, if an object A allocates an object B, and object B allocates an object C, then A's Dispose implementation must call Dispose on B, which must in turn call Dispose on C.

Wichtig

Der C++ Compiler unterstützt die deterministische Freigabe von Ressourcen und lässt keine direkte Implementierung der Dispose-Methode zu.The C++ compiler supports deterministic disposal of resources and does not allow direct implementation of the Dispose method.

Ein Objekt muss auch die Dispose-Methode seiner Basisklasse aufzurufen, wenn die Basisklasse IDisposableimplementiert.An object must also call the Dispose method of its base class if the base class implements IDisposable. Weitere Informationen zum Implementieren von IDisposable für eine Basisklasse und deren Unterklassen finden Sie im Abschnitt "iverwerfand the Vererbungs Hierarchie" des Themas IDisposable.For more information about implementing IDisposable on a base class and its subclasses, see the "IDisposable and the inheritance hierarchy" section in the IDisposable topic.

Wenn die Dispose-Methode eines Objekts mehrmals aufgerufen wird, muss das Objekt alle Aufrufe nach dem ersten ignorieren.If an object's Dispose method is called more than once, the object must ignore all calls after the first one. Das-Objekt darf keine Ausnahme auslösen, wenn die Dispose-Methode mehrmals aufgerufen wird.The object must not throw an exception if its Dispose method is called multiple times. Andere Instanzmethoden als Dispose können eine ObjectDisposedException auslösen, wenn bereits Ressourcen verworfen wurden.Instance methods other than Dispose can throw an ObjectDisposedException when resources are already disposed.

Benutzer erwarten möglicherweise, dass ein Ressourcentyp eine bestimmte Konvention verwendet, um einen zugewiesenen Zustand oder einen freigegebenen Zustand anzugeben.Users might expect a resource type to use a particular convention to denote an allocated state versus a freed state. Ein Beispiel hierfür sind Streamklassen, die üblicherweise als offen oder geschlossen angesehen werden.An example of this is stream classes, which are traditionally thought of as open or closed. Der Implementierer einer Klasse, die über eine solche Konvention verfügt, kann eine öffentliche Methode mit einem angepassten Namen implementieren, z. b. Close, der die Dispose-Methode aufruft.The implementer of a class that has such a convention might choose to implement a public method with a customized name, such as Close, that calls the Dispose method.

Da die Dispose-Methode explizit aufgerufen werden muss, besteht immer die Gefahr, dass die nicht verwalteten Ressourcen nicht freigegeben werden, da der Consumer eines Objekts seine Dispose-Methode nicht aufrufen kann.Because the Dispose method must be called explicitly, there is always a danger that the unmanaged resources will not be released, because the consumer of an object fails to call its Dispose method. Es gibt zwei Möglichkeiten, dies zu vermeiden:There are two ways to avoid this:

  • Wrappen Sie die verwaltete Ressource in einem Objekt, das von System.Runtime.InteropServices.SafeHandleabgeleitet ist.Wrap the managed resource in an object derived from System.Runtime.InteropServices.SafeHandle. Die Dispose-Implementierung ruft dann die Dispose-Methode der System.Runtime.InteropServices.SafeHandle-Instanzen auf.Your Dispose implementation then calls the Dispose method of the System.Runtime.InteropServices.SafeHandle instances. Weitere Informationen finden Sie im Abschnitt "SafeHandle Alternative" des Object.Finalize Themas.For more information, see "The SafeHandle alternative" section in the Object.Finalize topic.

  • Implementieren Sie einen Finalizer, um Ressourcen freizugeben, wenn Dispose nicht aufgerufen wird.Implement a finalizer to free resources when Dispose is not called. Standardmäßig ruft der Garbage Collector automatisch den Finalizer eines Objekts auf, bevor der zugehörige Speicher freigegeben wird.By default, the garbage collector automatically calls an object's finalizer before reclaiming its memory. Wenn jedoch die Dispose-Methode aufgerufen wurde, ist es in der Regel nicht erforderlich, dass der Garbage Collector den Finalizer des verworfenen Objekts aufruft.However, if the Dispose method has been called, it is typically unnecessary for the garbage collector to call the disposed object's finalizer. Um die automatische Finalisierung zu verhindern, können Dispose Implementierungen die GC.SuppressFinalize-Methode aufzurufen.To prevent automatic finalization, Dispose implementations can call the GC.SuppressFinalize method.

Wenn Sie ein Objekt verwenden, das auf nicht verwaltete Ressourcen zugreift, wie z. b. eine StreamWriter, empfiehlt es sich, die Instanz mit einer using-Anweisung zu erstellen.When you use an object that accesses unmanaged resources, such as a StreamWriter, a good practice is to create the instance with a using statement. Die using-Anweisung schließt den Stream automatisch und ruft Dispose für das-Objekt auf, wenn der Code, der ihn verwendet, abgeschlossen ist.The using statement automatically closes the stream and calls Dispose on the object when the code that is using it has completed. Ein Beispiel finden Sie in der StreamWriter-Klasse.For an example, see the StreamWriter class.

Gilt für:

Siehe auch