IDisposable.Dispose IDisposable.Dispose IDisposable.Dispose IDisposable.Dispose Method

Definizione

Esegue attività definite dall'applicazione, come rilasciare o reimpostare risorse non gestite.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 ()

Esempi

Nell'esempio seguente viene illustrato come è possibile implementare Dispose il metodo.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

Commenti

Utilizzare questo metodo per chiudere o rilasciare le risorse non gestite, ad esempio file, flussi e handle contenuti in un'istanza della classe che implementa questa interfaccia.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. Per convenzione, questo metodo viene utilizzato per tutte le attività associate alla liberazione di risorse utilizzate da un oggetto o alla preparazione di un oggetto per il riutilizzo.By convention, this method is used for all tasks associated with freeing resources held by an object, or preparing an object for reuse.

Avviso

Se si usa una classe che implementa l' IDisposable interfaccia, è necessario chiamare la relativa Dispose implementazione al termine dell'uso della classe.If you are using a class that implements the IDisposable interface, you should call its Dispose implementation when you are finished using the class. Per ulteriori informazioni, vedere la sezione "utilizzo di un oggetto che implementa IDisposable" nell' IDisposable argomento.For more information, see the "Using an object that implements IDisposable" section in the IDisposable topic.

Quando si implementa questo metodo, assicurarsi che tutte le risorse mantenute vengano liberate propagando la chiamata attraverso la gerarchia di contenimento.When implementing this method, ensure that all held resources are freed by propagating the call through the containment hierarchy. Se, ad esempio, un oggetto A alloca un oggetto b e l'oggetto b alloca un oggetto C, è necessario che l' Dispose implementazione di a Dispose chiami su B, che a sua volta Dispose deve chiamare su C.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.

Importante

Il C++ compilatore supporta l'eliminazione deterministica delle risorse e non consente l' Dispose implementazione diretta del metodo.The C++ compiler supports deterministic disposal of resources and does not allow direct implementation of the Dispose method.

Un oggetto deve anche chiamare il Dispose metodo della relativa classe di base se la classe base IDisposableimplementa.An object must also call the Dispose method of its base class if the base class implements IDisposable. Per ulteriori informazioni sull'implementazione IDisposable di in una classe base e sulle relative sottoclassi, vedere la sezione "IDisposable e la gerarchia IDisposable di ereditarietà" nell'argomento.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.

Se il metodo di Dispose un oggetto viene chiamato più di una volta, l'oggetto deve ignorare tutte le chiamate successive alla prima.If an object's Dispose method is called more than once, the object must ignore all calls after the first one. L'oggetto non deve generare un'eccezione se il Dispose relativo metodo viene chiamato più volte.The object must not throw an exception if its Dispose method is called multiple times. I metodi di istanza Dispose diversi da possono ObjectDisposedException generare un'eccezione quando le risorse sono già eliminate.Instance methods other than Dispose can throw an ObjectDisposedException when resources are already disposed.

Gli utenti potrebbero prevedere che un tipo di risorsa usi una convenzione specifica per indicare uno stato allocato rispetto a uno stato liberato.Users might expect a resource type to use a particular convention to denote an allocated state versus a freed state. Un esempio è costituito dalle classi di flusso, che vengono tradizionalmente considerate aperte o chiuse.An example of this is stream classes, which are traditionally thought of as open or closed. L'implementatore di una classe che dispone di tale convenzione può scegliere di implementare un metodo pubblico con un nome personalizzato, ad esempio Close, che chiama il Dispose metodo.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.

Poiché il Dispose metodo deve essere chiamato in modo esplicito, esiste sempre il rischio che le risorse non gestite non vengano rilasciate, perché il consumer di un oggetto non riesce Dispose a chiamare il relativo metodo.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. Esistono due modi per evitare questo problema:There are two ways to avoid this:

  • Eseguire il wrapping della risorsa gestita in un oggetto System.Runtime.InteropServices.SafeHandlederivato da.Wrap the managed resource in an object derived from System.Runtime.InteropServices.SafeHandle. L'implementazione chiama quindi il Dispose metodo delle System.Runtime.InteropServices.SafeHandle istanze di. DisposeYour Dispose implementation then calls the Dispose method of the System.Runtime.InteropServices.SafeHandle instances. Per ulteriori informazioni, vedere la sezione "alternativa SafeHandle" nell' Object.Finalize argomento.For more information, see "The SafeHandle alternative" section in the Object.Finalize topic.

  • Implementare un finalizzatore per liberare risorse quando Dispose non viene chiamato.Implement a finalizer to free resources when Dispose is not called. Per impostazione predefinita, il Garbage Collector chiama automaticamente il finalizzatore di un oggetto prima di recuperare la memoria.By default, the garbage collector automatically calls an object's finalizer before reclaiming its memory. Tuttavia, se il Dispose metodo è stato chiamato, in genere non è necessario che il Garbage Collector chiami il finalizzatore dell'oggetto eliminato.However, if the Dispose method has been called, it is typically unnecessary for the garbage collector to call the disposed object's finalizer. Per evitare la finalizzazione automatica Dispose , le implementazioni possono GC.SuppressFinalize chiamare il metodo.To prevent automatic finalization, Dispose implementations can call the GC.SuppressFinalize method.

Quando si utilizza un oggetto che accede a risorse non gestite, ad esempio StreamWriter, è consigliabile creare l'istanza con un' using istruzione.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. L' using istruzione chiude automaticamente il flusso e chiama Dispose sull'oggetto quando il codice che lo usa è stato completato.The using statement automatically closes the stream and calls Dispose on the object when the code that is using it has completed. Per un esempio, vedere la StreamWriter classe.For an example, see the StreamWriter class.

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