Abrufen des Status einer asynchronen OperationPolling for the Status of an Asynchronous Operation

Anwendungen, die während des Wartens auf die Ergebnisse eines asynchronen Vorgangs weiterarbeiten können, sollten nicht blockiert werden, bis der Vorgang abgeschlossen ist.Applications that can do other work while waiting for the results of an asynchronous operation should not block waiting until the operation completes. Verwenden Sie eine der folgenden Optionen, um Anweisungen weiter auszuführen, während Sie darauf warten, dass ein asynchroner Vorgang abgeschlossen wird:Use one of the following options to continue executing instructions while waiting for an asynchronous operation to complete:

BeispielExample

Das folgende Codebeispiel demonstriert die Verwendung von asynchronen Methoden in der Dns-Klasse, um Informationen aus dem Domain Name System für einen benutzerdefinierten Computer abzurufen.The following code example demonstrates using asynchronous methods in the Dns class to retrieve Domain Name System information for a user-specified computer. Dieses Beispiel startet den asynchronen Vorgang und gibt dann Punkte („.“) in der Konsole aus, bis der Vorgang abgeschlossen ist.This example starts the asynchronous operation and then prints periods (".") at the console until the operation is complete. Beachten Sie, dass NULL (Nichts in Visual Basic) für die Parameter BeginGetHostByNameAsyncCallback und Object übergeben wird, da diese Argumente bei diesem Ansatz nicht benötigt werden.Note that null (Nothing in Visual Basic) is passed for the BeginGetHostByNameAsyncCallback and Object parameters because these arguments are not required when using this approach.

/*
The following example demonstrates using asynchronous methods to
get Domain Name System information for the specified host computer.
This example polls to detect the end of the asynchronous operation.
*/

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

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class PollUntilOperationCompletes
    {
        static void UpdateUserInterface()
        {
            // Print a period to indicate that the application
            // is still working on the request.
            Console.Write(".");
        }
        public static void Main(string[] args)
        {
            // Make sure the caller supplied a host name.
            if (args.Length == 0 || args[0].Length == 0)
            {
                // Print a message and exit.
                Console.WriteLine("You must specify the name of a host computer.");
                return;
            }
            // Start the asychronous request for DNS information.
            IAsyncResult result = Dns.BeginGetHostEntry(args[0], null, null);
            Console.WriteLine("Processing request for information...");
            
            // Poll for completion information.
            // Print periods (".") until the operation completes.
            while (result.IsCompleted != true)
            {
                UpdateUserInterface();
            }
            // The operation is complete. Process the results.
            // Print a new line.
            Console.WriteLine();
            try 
            {
                IPHostEntry host = Dns.EndGetHostEntry(result);
                string[] aliases = host.Aliases;
                IPAddress[] addresses = host.AddressList;
                if (aliases.Length > 0)
                {
                    Console.WriteLine("Aliases");
                    for (int i = 0; i < aliases.Length; i++)
                    {
                        Console.WriteLine("{0}", aliases[i]);
                    }
                }
                if (addresses.Length > 0)
                {
                    Console.WriteLine("Addresses");
                    for (int i = 0; i < addresses.Length; i++)
                    {
                        Console.WriteLine("{0}",addresses[i].ToString());
                    }
                }
            }
            catch (SocketException e)
            {
                Console.WriteLine("An exception occurred while processing the request: {0}", e.Message);
            }
        }
    }
}

'The following example demonstrates using asynchronous methods to
'get Domain Name System information for the specified host computer.
'This example polls to detect the end of the asynchronous operation.

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

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class PollUntilOperationCompletes
        Shared Sub UpdateUserInterface()
            ' Print a period to indicate that the application
            ' is still working on the request.
            Console.Write(".")
        End Sub
        Public Shared Sub Main(args() as String)
            ' Make sure the caller supplied a host name.
            If(args.Length = 0)
                ' Print a message and exit.
                Console.WriteLine("You must specify the name of a host computer.")
                End
            End If
            ' Start the asynchronous request for DNS information.
            Dim result as IAsyncResult= Dns.BeginGetHostEntry(args(0), Nothing, Nothing)
            Console.WriteLine("Processing request for information...")
            
            ' Poll for completion information.
            ' Print periods (".") until the operation completes.
            Do while result.IsCompleted <> True
                UpdateUserInterface()
            Loop
            ' The operation is complete. Process the results.
            ' Print a new line.
            Console.WriteLine()
            Try 
                Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
                Dim  aliases() as String = host.Aliases
                Dim addresses() as IPAddress = host.AddressList
                Dim i as Integer
                If aliases.Length > 0
                    Console.WriteLine("Aliases")
                    For i = 0 To aliases.Length -1 
                        Console.WriteLine("{0}", aliases(i))
                    Next i
                End If
                If addresses.Length > 0
                    Console.WriteLine("Addresses")
                    For i = 0 To addresses.Length -1
                        Console.WriteLine("{0}", addresses(i).ToString())
                    Next i
                End If
            Catch e as SocketException
                  Console.WriteLine("An exception occurred while processing the request: {0}", e.Message)
            End Try
        End Sub
    End Class
End Namespace

Siehe auchSee also