IDisposable.Dispose Metoda

Definice

Provede aplikací definované úlohy spojené s uvolněním nebo resetováním nespravovaných prostředků.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 ()

Příklady

Následující příklad ukazuje, jak lze implementovat Dispose metodu.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

Poznámky

Tuto metodu použijte k zavření nebo uvolnění nespravovaných prostředků, jako jsou soubory, datové proudy a popisovače držené instancí třídy, která implementuje toto rozhraní.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. Podle konvence je tato metoda používána pro všechny úlohy spojené s uvolněním prostředků držených objektem nebo připravuje objekt pro opakované použití.By convention, this method is used for all tasks associated with freeing resources held by an object, or preparing an object for reuse.

Upozornění

Pokud používáte třídu, která implementuje IDisposable rozhraní, měli byste zavolat jeho Dispose implementaci po dokončení používání třídy.If you are using a class that implements the IDisposable interface, you should call its Dispose implementation when you are finished using the class. Další informace naleznete v části "použití objektu, který implementuje rozhraní IDisposable" v IDisposable tématu.For more information, see the "Using an object that implements IDisposable" section in the IDisposable topic.

Při implementaci této metody zajistěte, aby všechny držené prostředky byly uvolněny rozšířením volání prostřednictvím hierarchie omezení.When implementing this method, ensure that all held resources are freed by propagating the call through the containment hierarchy. Například pokud objekt A přiděluje objekt B a objekt B přiděluje objekt C, pak Dispose implementace musí zavolat Dispose na B, který musí volat v Dispose 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.

Důležité

Kompilátor C++ podporuje deterministické odstranění prostředků a neumožňuje přímou implementaci Dispose metody.The C++ compiler supports deterministic disposal of resources and does not allow direct implementation of the Dispose method.

Objekt musí také volat Dispose metodu své základní třídy, pokud implementuje základní třída IDisposable .An object must also call the Dispose method of its base class if the base class implements IDisposable. Další informace o implementaci IDisposable na základní třídu a jejích podtřídách naleznete v části IDisposable a Hierarchie dědičnosti v IDisposable tématu.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.

Je-li Dispose metoda objektu volána více než jednou, objekt musí ignorovat všechna volání po prvním z nich.If an object's Dispose method is called more than once, the object must ignore all calls after the first one. Objekt nesmí vyvolat výjimku Dispose , pokud je jeho metoda volána vícekrát.The object must not throw an exception if its Dispose method is called multiple times. Metody instance jiné než Dispose mohou vyvolat výjimku ObjectDisposedException , pokud jsou prostředky již uvolněny.Instance methods other than Dispose can throw an ObjectDisposedException when resources are already disposed.

Uživatelé můžou očekávat, že typ prostředku bude používat konkrétní konvenci k označení přiděleného stavu oproti uvolněnému stavu.Users might expect a resource type to use a particular convention to denote an allocated state versus a freed state. Příkladem jsou třídy streamu, které jsou tradičně považovány za otevřené nebo uzavřené.An example of this is stream classes, which are traditionally thought of as open or closed. Implementátor třídy, která má takovou konvenci, se může rozhodnout implementovat veřejnou metodu s přizpůsobeným názvem, například Close , který volá Dispose metodu.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.

Vzhledem k tomu, že Dispose Metoda musí být volána explicitně, existuje vždy nebezpečí, že nespravované prostředky nebudou uvolněny, protože příjemce objektu nemůže volat svou Dispose metodu.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. Neexistují dva způsoby, jak se tomu vyhnout:There are two ways to avoid this:

  • Zabalení spravovaného prostředku v objektu odvozeném z System.Runtime.InteropServices.SafeHandle .Wrap the managed resource in an object derived from System.Runtime.InteropServices.SafeHandle. Vaše Dispose implementace pak zavolá Dispose metodu System.Runtime.InteropServices.SafeHandle instancí.Your Dispose implementation then calls the Dispose method of the System.Runtime.InteropServices.SafeHandle instances. Další informace naleznete v části "alternativa SafeHandle" v Object.Finalize tématu.For more information, see "The SafeHandle alternative" section in the Object.Finalize topic.

  • Implementujte finalizační metodu pro uvolnění prostředků Dispose , když se nevolá.Implement a finalizer to free resources when Dispose is not called. Ve výchozím nastavení systém uvolňování paměti automaticky volá finalizační metodu objektu před tím, než se uvolní jeho paměť.By default, the garbage collector automatically calls an object's finalizer before reclaiming its memory. Nicméně, pokud byla Dispose metoda volána, je obvykle zbytečné, aby systém uvolňování paměti volal finalizační metodu odstraněného objektu.However, if the Dispose method has been called, it is typically unnecessary for the garbage collector to call the disposed object's finalizer. Chcete-li zabránit automatické finalizaci, Dispose implementace mohou volat GC.SuppressFinalize metodu.To prevent automatic finalization, Dispose implementations can call the GC.SuppressFinalize method.

Při použití objektu, který přistupuje k nespravovaným prostředkům, jako je StreamWriter dobrý postup, je vytvoření instance s using příkazem.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. usingPříkaz automaticky uzavře datový proud a volá Dispose objekt, když kód, který ho používá, byl dokončen.The using statement automatically closes the stream and calls Dispose on the object when the code that is using it has completed. Příklad naleznete v tématu StreamWriter Třída.For an example, see the StreamWriter class.

Platí pro

Viz také