Compartir a través de


Utilizar un delegado AsyncCallback y un objeto State

Actualización: noviembre 2007

Aquellas aplicaciones que pueden realizar otra tarea mientras esperan los resultados de una operación asincrónica, no se deberían bloquear mientras esperan a que la operación finalice. Utilice una de las siguientes opciones para seguir ejecutando instrucciones mientras se está a la espera de que una operación asincrónica finalice:

  • Utilice un delegado AsyncCallback para procesar los resultados de la operación asincrónica en un subproceso independiente. Este tema muestra la ejecución de dicho procedimiento.

  • Utilice la propiedad IsCompleted de la interfaz IAsyncResult devuelta por el método BeginnombreDeOperación de la operación asincrónica para determinar si la operación se ha completado. Para obtener un ejemplo de este procedimiento, vea Sondear el estado de una operación asincrónica.

Ejemplo

El siguiente ejemplo de código muestra cómo utilizar los métodos asincrónicos en la clase Dns con el fin de recuperar información sobre el Sistema de nombres de dominio (DNS) para equipos especificados por el usuario. Este ejemplo define y utiliza la clase HostRequest para almacenar información de estado. Un objeto HostRequest se crea para cada nombre de equipo escrito por el usuario. Este objeto se pasa al método BeginGetHostByName. Se llama al método ProcessDnsInformation cada vez que una solicitud finaliza. El objeto HostRequest se recupera utilizando la propiedad AsyncState. El método ProcessDnsInformation utiliza el objeto HostRequest para almacenar un IPHostEntry devuelto por la solicitud o un SocketException producido por la solicitud. Una vez que todas las solicitudes han finalizado, la aplicación recorre en iteración los objetos HostRequest y muestra la información DNS o mensaje de error SocketException.

' The following example demonstrates using asynchronous methods to
' get Domain Name System information for the specified host computer.

Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Collections

Namespace Examples.AdvancedProgramming.AsynchronousOperations
' Create a state object that holds each requested host name, 
' an associated IPHostEntry object or a SocketException.
    Public Class HostRequest
        ' Stores the requested host name.
        Dim hostNameValue as string
        ' Stores any SocketException returned by the Dns EndGetHostByName method.
        Dim e as SocketException
        ' Stores an IPHostEntry returned by the Dns EndGetHostByName method.
        Dim entry as IPHostEntry

        Public Sub New(name as String)
            hostNameValue = name
        End Sub

        ReadOnly Public Property HostName as String
            Get
                return hostNameValue
            End Get
        End Property

        Public Property ExceptionObject as SocketException
            Get
                return e
            End Get
            Set
                 e = value
            End Set
        End Property

        Public Property HostEntry as IPHostEntry
            Get
                return entry
            End Get
            Set
                entry = value
            End Set
        End Property
    End Class

    Public Class UseDelegateAndStateForAsyncCallback
        ' The number of pending requests.
        Dim Shared requestCounter as Integer
        Dim Shared hostData as ArrayList = new ArrayList()

        Shared Sub UpdateUserInterface()
            ' Print a message to indicate that the application
            ' is still working on the remaining requests.
            Console.WriteLine("{0} requests remaining.", requestCounter)
        End Sub

        Public Shared Sub Main()
            ' Create the delegate that will process the results of the 
            ' asynchronous request.
            Dim callBack as AsyncCallback = AddressOf ProcessDnsInformation
            Dim host as string

            Do
                Console.Write(" Enter the name of a host computer or <enter> to finish: ")
                host = Console.ReadLine()
                If host.Length > 0
                    ' Increment the request counter in a thread safe manner.
                    Interlocked.Increment (requestCounter)
                    ' Create and store the state object for this request.
                    Dim  request as HostRequest = new HostRequest(host)
                    hostData.Add(request)
                    ' Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, request)
                 End If
            Loop While host.Length > 0

            ' The user has entered all of the host names for lookup.
            ' Now wait until the threads complete.
            Do While requestCounter > 0
                UpdateUserInterface()
            Loop

            ' Display the results.
            For Each r as HostRequest In hostData
                    If IsNothing(r.ExceptionObject) = False
                        Console.WriteLine( _ 
                          "Request for host {0} returned the following error: {1}.", _
                          r.HostName, r.ExceptionObject.Message)
                    Else
                        ' Get the results.
                        Dim h as IPHostEntry = r.HostEntry
                        Dim aliases() as String = h.Aliases
                        Dim addresses() as IPAddress = h.AddressList
                        Dim j, k as Integer

                        If aliases.Length > 0
                            Console.WriteLine("Aliases for {0}", r.HostName)
                            For j = 0 To aliases.Length - 1
                                Console.WriteLine("{0}", aliases(j))
                            Next j
                        End If
                        If addresses.Length > 0
                            Console.WriteLine("Addresses for {0}", r.HostName)
                            For k = 0 To addresses.Length -1
                                Console.WriteLine("{0}",addresses(k).ToString())
                            Next k
                        End If
                    End If
            Next r
       End Sub

        ' The following method is invoked when each asynchronous operation completes.
        Shared Sub ProcessDnsInformation(result as IAsyncResult)
           ' Get the state object associated with this request.
           Dim request as HostRequest= CType(result.AsyncState,HostRequest)
            Try 
                ' Get the results and store them in the state object.
                Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
                request.HostEntry = host
            Catch e as SocketException
                ' Store any SocketExceptions.
                request.ExceptionObject = e
            Finally 
                ' Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(requestCounter)
            End Try
        End Sub
    End Class
End Namespace
/*
The following example demonstrates using asynchronous methods to
get Domain Name System information for the specified host computer.
*/

using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Collections;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
// Create a state object that holds each requested host name, 
// an associated IPHostEntry object or a SocketException.
    public class HostRequest
    {
        // Stores the requested host name.
        private string hostName;
        // Stores any SocketException returned by the Dns EndGetHostByName method.
        private SocketException e;
        // Stores an IPHostEntry returned by the Dns EndGetHostByName method.
        private IPHostEntry entry;

        public HostRequest(string name)
        {
            hostName = name;
        }

        public string HostName
        {
            get 
            {
                return hostName;
            }
        }

        public SocketException ExceptionObject
        {
            get 
            {
                return e;
            }
            set 
            {
                 e = value;
            }
        }

        public IPHostEntry HostEntry
        {
            get 
            {
                return entry;
            }
            set 
            {
                entry = value;
            }
        }
    }

    public class UseDelegateAndStateForAsyncCallback
    {
        // The number of pending requests.
        static int requestCounter;
        static ArrayList hostData = new ArrayList();
        static void UpdateUserInterface()
        {
            // Print a message to indicate that the application
            // is still working on the remaining requests.
            Console.WriteLine("{0} requests remaining.", requestCounter);
        }
        public static void Main()
        {
            // Create the delegate that will process the results of the 
            // asynchronous request.
            AsyncCallback callBack = new AsyncCallback(ProcessDnsInformation);
            string host;
            do
            {
                Console.Write(" Enter the name of a host computer or <enter> to finish: ");
                host = Console.ReadLine();
                if (host.Length > 0)
                {
                    // Increment the request counter in a thread safe manner.
                    Interlocked.Increment(ref requestCounter);
                    // Create and store the state object for this request.
                    HostRequest request = new HostRequest(host);
                    hostData.Add(request);
                    // Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, request);
                 }
            } while (host.Length > 0);
            // The user has entered all of the host names for lookup.
            // Now wait until the threads complete.
            while (requestCounter > 0)
            {
                UpdateUserInterface();
            }
            // Display the results.
            foreach(HostRequest r in hostData)
            {
                    if (r.ExceptionObject != null)
                    {
                        Console.WriteLine("Request for host {0} returned the following error: {1}.", 
                            r.HostName, r.ExceptionObject.Message);
                    }
                    else
                    {
                        // Get the results.
                        IPHostEntry h = r.HostEntry;
                        string[] aliases = h.Aliases;
                        IPAddress[] addresses = h.AddressList;
                        if (aliases.Length > 0)
                        {
                            Console.WriteLine("Aliases for {0}", r.HostName);
                            for (int j = 0; j < aliases.Length; j++)
                            {
                                Console.WriteLine("{0}", aliases[j]);
                            }
                        }
                        if (addresses.Length > 0)
                        {
                            Console.WriteLine("Addresses for {0}", r.HostName);
                            for (int k = 0; k < addresses.Length; k++)
                            {
                                Console.WriteLine("{0}",addresses[k].ToString());
                            }
                        }
                    }
            }
       }

        // The following method is invoked when each asynchronous operation completes.
        static void ProcessDnsInformation(IAsyncResult result)
        {
           // Get the state object associated with this request.
           HostRequest request = (HostRequest) result.AsyncState;
            try 
            {
                // Get the results and store them in the state object.
                IPHostEntry host = Dns.EndGetHostEntry(result);
                request.HostEntry = host;
            }
            catch (SocketException e)
            {
                // Store any SocketExceptions.
                request.ExceptionObject = e;
            }
            finally 
            {
                // Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(ref requestCounter);
            }
        }
    }
}

Vea también

Conceptos

Información general sobre el modelo asincrónico basado en eventos

Utilizar un delegado AsyncCallback para finalizar una operación asincrónica

Otros recursos

Modelos de diseño para la programación asincrónica