IDisposable Interfaccia

Definizione

public interface class IDisposable

[System.Runtime.InteropServices.ComVisible(true)]
public interface IDisposable

type IDisposable = interface

Public Interface IDisposable

Derivato

DbLinq.Util.BaseLock

Microsoft.Build.Debugging.DebuggerManager.IslandThread

Microsoft.Build.Evaluation.ProjectCollection

Microsoft.Build.Execution.BuildManager

Microsoft.Extensions.Caching.Memory.ICacheEntry

Altro…

Attributi

ComVisibleAttribute

Esempi

Nell'esempio seguente viene illustrato come creare una classe di risorse che implementa IDisposable l'interfaccia.The following example demonstrates how to create a resource class that implements the IDisposable interface.

#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

L'uso principale di questa interfaccia consiste nel rilasciare le risorse non gestite.The primary use of this interface is to release unmanaged resources. Il Garbage Collector rilascia automaticamente la memoria allocata a un oggetto gestito quando tale oggetto non viene più utilizzato.The garbage collector automatically releases the memory allocated to a managed object when that object is no longer used. Tuttavia, non è possibile prevedere quando si verificherà Garbage Collection.However, it is not possible to predict when garbage collection will occur. Inoltre, il Garbage Collector non conosce le risorse non gestite, ad esempio gli handle di finestra, né i file e i flussi aperti.Furthermore, the garbage collector has no knowledge of unmanaged resources such as window handles, or open files and streams.

Usare il Dispose metodo di questa interfaccia per rilasciare in modo esplicito le risorse non gestite insieme al Garbage Collector.Use the Dispose method of this interface to explicitly release unmanaged resources in conjunction with the garbage collector. Il consumer di un oggetto può chiamare questo metodo quando l'oggetto non è più necessario.The consumer of an object can call this method when the object is no longer needed.

Poiché l' IDisposable.Dispose implementazione viene chiamata dal consumer di un tipo quando le risorse di proprietà di un'istanza non sono più necessarie, è necessario eseguire il wrapping dell'oggetto gestito SafeHandle in un (alternativa consigliata) oppure eseguire l'override Object.Finalizedi.per liberare le risorse non gestite nel caso in cui il consumer dimentichi di chiamare Dispose.Because the IDisposable.Dispose implementation is called by the consumer of a type when the resources owned by an instance are no longer needed, you should either wrap the managed object in a SafeHandle (the recommended alternative), or you should override Object.Finalize to free unmanaged resources in the event that the consumer forgets to call Dispose.

Per una descrizione dettagliata del modo in cui vengono usate Object.Finalize questa interfaccia e il metodo, vedere gli argomenti Garbage Collection e Implementing a Dispose Method .For a detailed discussion about how this interface and the Object.Finalize method are used, see the Garbage Collection and Implementing a Dispose Method topics.

Uso di un oggetto che implementa IDisposableUsing an object that implements IDisposable

Se l'app usa semplicemente un oggetto che implementa l' IDisposable interfaccia, è necessario chiamare l' IDisposable.Dispose implementazione dell'oggetto al termine dell'uso.If your app simply uses an object that implements the IDisposable interface, you should call the object's IDisposable.Dispose implementation when you are finished using it. A seconda del linguaggio di programmazione, è possibile eseguire questa operazione in uno dei due modi seguenti:Depending on your programming language, you can do this in one of two ways:

• Utilizzando un costrutto di linguaggio, ad using esempio l' C# istruzione in e Visual Basic.By using a language construct such as the using statement in C# and Visual Basic.

• Eseguendo il wrapping della chiamata all' IDisposable.Dispose implementazione in un try / finally blocco.By wrapping the call to the IDisposable.Dispose implementation in a try/finally block.

C# E Visual Basic istruzione usingThe C# and Visual Basic Using statement

Se il linguaggio supporta un costrutto, ad esempio l'istruzione C# using in e l'istruzione using in Visual Basic, è possibile usarlo anziché chiamare IDisposable.Dispose in modo esplicito.If your language supports a construct such as the using statement in C# and the Using statement in Visual Basic, you can use it instead of explicitly calling IDisposable.Dispose yourself. Nell'esempio seguente viene usato questo approccio per la WordCount definizione di una classe che conserva le informazioni su un file e il numero di parole al suo interno.The following example uses this approach in defining a WordCount class that preserves information about a file and the number of words in it.

using System;
using System.IO;
using System.Text.RegularExpressions;

public class WordCount
{
   private String filename = String.Empty;
   private int nWords = 0;
   private String pattern = @"\b\w+\b"; 

   public WordCount(string filename)
   {
      if (! File.Exists(filename))
         throw new FileNotFoundException("The file does not exist.");
      
      this.filename = filename;
      string txt = String.Empty;
      using (StreamReader sr = new StreamReader(filename)) {
         txt = sr.ReadToEnd();
      }
      nWords = Regex.Matches(txt, pattern).Count;
   }
   
   public string FullName
   { get { return filename; } }
   
   public string Name
   { get { return Path.GetFileName(filename); } }
   
   public int Count 
   { get { return nWords; } }
}   

Imports System.IO
Imports System.Text.RegularExpressions

Public Class WordCount
   Private filename As String
   Private nWords As Integer
   Private pattern As String = "\b\w+\b" 

   Public Sub New(filename As String)
      If Not File.Exists(filename) Then
         Throw New FileNotFoundException("The file does not exist.")
      End If   
      
      Me.filename = filename
      Dim txt As String = String.Empty
      Using sr As New StreamReader(filename)
         txt = sr.ReadToEnd()
      End Using
      nWords = Regex.Matches(txt, pattern).Count
   End Sub
   
   Public ReadOnly Property FullName As String
      Get
         Return filename
      End Get   
   End Property
   
   Public ReadOnly Property Name As String
      Get
         Return Path.GetFileName(filename)
      End Get   
   End Property
   
   Public ReadOnly Property Count As Integer
      Get
         Return nWords
      End Get
   End Property
End Class

L' using istruzione è in realtà una praticità sintattica.The using statement is actually a syntactic convenience. In fase di compilazione, il compilatore del linguaggio implementa il linguaggio intermedio (il try ) per un / finally blocco.At compile time, the language compiler implements the intermediate language (IL) for a try/finally block.

Per ulteriori informazioni sull' using istruzione, vedere gli argomenti istruzione using o istruzione using .For more information about the using statement, see the Using Statement or using Statement topics.

Blocco try/finallyThe Try/Finally block

Se il linguaggio di programmazione non supporta un costrutto come using l'istruzione C# in o Visual Basic o se si preferisce non usarlo, è possibile chiamare IDisposable.Dispose finally l'implementazione dal blocco di un try /istruzione. finallyIf your programming language does not support a construct like the using statement in C# or Visual Basic, or if you prefer not to use it, you can call the IDisposable.Dispose implementation from the finally block of a try/finally statement. Nell' using esempio seguente il blocco nell'esempio precedente viene sostituito con un try / finally blocco.The following example replaces the using block in the previous example with a try/finally block.

using System;
using System.IO;
using System.Text.RegularExpressions;

public class WordCount
{
   private String filename = String.Empty;
   private int nWords = 0;
   private String pattern = @"\b\w+\b"; 

   public WordCount(string filename)
   {
      if (! File.Exists(filename))
         throw new FileNotFoundException("The file does not exist.");
      
      this.filename = filename;
      string txt = String.Empty;
      StreamReader sr = null;
      try {
         sr = new StreamReader(filename);
         txt = sr.ReadToEnd();
      }
      finally {
         if (sr != null) sr.Dispose();     
      }
      nWords = Regex.Matches(txt, pattern).Count;
   }
   
   public string FullName
   { get { return filename; } }
   
   public string Name
   { get { return Path.GetFileName(filename); } }
   
   public int Count 
   { get { return nWords; } }
}   

Imports System.IO
Imports System.Text.RegularExpressions

Public Class WordCount
   Private filename As String
   Private nWords As Integer
   Private pattern As String = "\b\w+\b" 

   Public Sub New(filename As String)
      If Not File.Exists(filename) Then
         Throw New FileNotFoundException("The file does not exist.")
      End If   
      
      Me.filename = filename
      Dim txt As String = String.Empty
      Dim sr As StreamReader = Nothing
      Try
         sr = New StreamReader(filename)
         txt = sr.ReadToEnd()
      Finally
         If sr IsNot Nothing Then sr.Dispose() 
      End Try
      nWords = Regex.Matches(txt, pattern).Count
   End Sub
   
   Public ReadOnly Property FullName As String
      Get
         Return filename
      End Get   
   End Property
   
   Public ReadOnly Property Name As String
      Get
         Return Path.GetFileName(filename)
      End Get   
   End Property
   
   Public ReadOnly Property Count As Integer
      Get
         Return nWords
      End Get
   End Property
End Class

Per ulteriori informazioni sul try / finally modello, vedere try... Rileva... Istruzione finally, try-finallyo try-finally.For more information about the try/finally pattern, see Try...Catch...Finally Statement, try-finally, or try-finally Statement.

Implementazione di IDisposableImplementing IDisposable

È consigliabile implementare IDisposable solo se il tipo utilizza direttamente le risorse non gestite.You should implement IDisposable only if your type uses unmanaged resources directly. I consumer del tipo possono chiamare IDisposable.Dispose l'implementazione di per liberare risorse quando l'istanza non è più necessaria.The consumers of your type can call your IDisposable.Dispose implementation to free resources when the instance is no longer needed. Per gestire i casi in cui non è possibile Disposechiamare, è necessario usare una classe derivata da SafeHandle per eseguire il wrapping delle risorse non gestite oppure eseguire l'override del Object.Finalize metodo per un tipo di riferimento.To handle cases in which they fail to call Dispose, you should either use a class derived from SafeHandle to wrap the unmanaged resources, or you should override the Object.Finalize method for a reference type. In entrambi i casi, si utilizza Dispose il metodo per eseguire la pulizia necessaria dopo l'utilizzo delle risorse non gestite, ad esempio la liberazione, il rilascio o la reimpostazione delle risorse non gestite.In either case, you use the Dispose method to perform whatever cleanup is necessary after using the unmanaged resources, such as freeing, releasing, or resetting the unmanaged resources.

IDisposable e gerarchia di ereditarietàIDisposable and the inheritance hierarchy

Una classe di base con sottoclassi che devono essere Disposable deve implementare IDisposable come indicato di seguito.A base class with subclasses that should be disposable must implement IDisposable as follows. È consigliabile usare questo modello ogni volta che IDisposable si implementa in qualsiasi tipo sealed nonNotInheritable (in Visual Basic).You should use this pattern whenever you implement IDisposable on any type that isn't sealed (NotInheritable in Visual Basic).

• Deve fornire un metodo pubblico, non virtuale Dispose() e un metodo virtuale Dispose(Boolean disposing) protetto.It should provide one public, non-virtual Dispose() method and a protected virtual Dispose(Boolean disposing) method.

• Il Dispose() metodo deve chiamare Dispose(true) e deve impedire la finalizzazione per le prestazioni.The Dispose() method must call Dispose(true) and should suppress finalization for performance.

• Il tipo di base non deve includere alcun finalizzatore.The base type should not include any finalizers.

Il frammento di codice seguente riflette il modello Dispose per le classi base.The following code fragment reflects the dispose pattern for base classes. Si presuppone che il tipo non esegua l' Object.Finalize override del metodo.It assumes that your type does not override the Object.Finalize method.

using Microsoft.Win32.SafeHandles;
using System;
using System.Runtime.InteropServices;

class BaseClass : IDisposable
{
   // Flag: Has Dispose already been called?
   bool disposed = false;
   // Instantiate a SafeHandle instance.
   SafeHandle handle = new SafeFileHandle(IntPtr.Zero, true);
   
   // Public implementation of Dispose pattern callable by consumers.
   public void Dispose()
   { 
      Dispose(true);
      GC.SuppressFinalize(this);           
   }
   
   // Protected implementation of Dispose pattern.
   protected virtual void Dispose(bool disposing)
   {
      if (disposed)
         return; 
      
      if (disposing) {
         handle.Dispose();
         // Free any other managed objects here.
         //
      }
      
      disposed = true;
   }
}

Imports Microsoft.Win32.SafeHandles
Imports System.Runtime.InteropServices

Class BaseClass : Implements IDisposable
   ' Flag: Has Dispose already been called?
   Dim disposed As Boolean = False
   ' Instantiate a SafeHandle instance.
   Dim handle As SafeHandle = New SafeFileHandle(IntPtr.Zero, True)

   ' Public implementation of Dispose pattern callable by consumers.
   Public Sub Dispose() _
              Implements IDisposable.Dispose
      Dispose(True)
      GC.SuppressFinalize(Me)           
   End Sub
   
   ' Protected implementation of Dispose pattern.
   Protected Overridable Sub Dispose(disposing As Boolean)
      If disposed Then Return
      
      If disposing Then
         handle.Dispose()
         ' Free any other managed objects here.
         '
      End If
      
      disposed = True
   End Sub
End Class

Se si esegue l'override Object.Finalize del metodo, la classe deve implementare il modello seguente.If you do override the Object.Finalize method, your class should implement the following pattern.

using System;

class BaseClass : IDisposable
{
   // Flag: Has Dispose already been called?
   bool disposed = false;
   
   // Public implementation of Dispose pattern callable by consumers.
   public void Dispose()
   { 
      Dispose(true);
      GC.SuppressFinalize(this);           
   }
   
   // Protected implementation of Dispose pattern.
   protected virtual void Dispose(bool disposing)
   {
      if (disposed)
         return; 
      
      if (disposing) {
         // Free any other managed objects here.
         //
      }
      
      // Free any unmanaged objects here.
      //
      disposed = true;
   }

   ~BaseClass()
   {
      Dispose(false);
   }
}

Class BaseClass : Implements IDisposable
   ' Flag: Has Dispose already been called?
   Dim disposed As Boolean = False
   
   ' Public implementation of Dispose pattern callable by consumers.
   Public Sub Dispose() _
              Implements IDisposable.Dispose
      Dispose(True)
      GC.SuppressFinalize(Me)           
   End Sub
   
   ' Protected implementation of Dispose pattern.
   Protected Overridable Sub Dispose(disposing As Boolean)
      If disposed Then Return
      
      If disposing Then
         ' Free any other managed objects here.
         '
      End If
      
      ' Free any unmanaged objects here.
      '
      disposed = True
   End Sub

   Protected Overrides Sub Finalize()
      Dispose(False)      
   End Sub
End Class

Le sottoclassi devono implementare il modello Disposable come segue:Subclasses should implement the disposable pattern as follows:

• È necessario eseguire l'override di Dispose(Boolean) e chiamare l'implementazione Dispose(Boolean) della classe di base.They must override Dispose(Boolean) and call the base class Dispose(Boolean) implementation.

• Possono fornire un finalizzatore, se necessario.They can provide a finalizer if needed. Il finalizzatore deve chiamare Dispose(false).The finalizer must call Dispose(false).

Si noti che le classi derivate non IDisposable implementano l'interfaccia e non includono un Dispose metodo senza parametri.Note that derived classes do not themselves implement the IDisposable interface and do not include a parameterless Dispose method. Eseguono solo l'override del metodo Dispose(Boolean) della classe base.They only override the base class Dispose(Boolean) method.

Il frammento di codice seguente riflette il modello Dispose per le classi derivate.The following code fragment reflects the dispose pattern for derived classes. Si presuppone che il tipo non esegua l' Object.Finalize override del metodo.It assumes that your type does not override the Object.Finalize method.

using Microsoft.Win32.SafeHandles;
using System;
using System.Runtime.InteropServices;

class DerivedClass : BaseClass
{
   // Flag: Has Dispose already been called?
   bool disposed = false;
   // Instantiate a SafeHandle instance.
   SafeHandle handle = new SafeFileHandle(IntPtr.Zero, true);

   // Protected implementation of Dispose pattern.
   protected override void Dispose(bool disposing)
   {
      if (disposed)
         return; 
      
      if (disposing) {
         handle.Dispose();
         // Free any other managed objects here.
         //
      }
      
      // Free any unmanaged objects here.
      //

      disposed = true;
      // Call base class implementation.
      base.Dispose(disposing);
   }
}

Imports Microsoft.Win32.SafeHandles
Imports System.Runtime.InteropServices

Class DerivedClass : Inherits BaseClass 
   ' Flag: Has Dispose already been called?
   Dim disposed As Boolean = False
   ' Instantiate a SafeHandle instance.
   Dim handle As SafeHandle = New SafeFileHandle(IntPtr.Zero, True)

   ' Protected implementation of Dispose pattern.
   Protected Overrides Sub Dispose(disposing As Boolean)
      If disposed Then Return
      
      If disposing Then
         handle.Dispose()
         ' Free any other managed objects here.
         '
      End If
      
      ' Free any unmanaged objects here.
      '
      disposed = True
      
      ' Call base class implementation.
      MyBase.Dispose(disposing)
   End Sub
End Class

Metodi

Si applica a

Vedi anche

• SafeFileHandle
• Implementazione di un metodo DisposeImplementing a Dispose Method