AsyncCallback 代理人

定義

命名空間:

System

組件:

System.Runtime.dll

組件:

mscorlib.dll

組件:

netstandard.dll

參考要在對應之非同步作業完成時呼叫的方法。

C#

public delegate void AsyncCallback(IAsyncResult ar);

C#

[System.Serializable]
public delegate void AsyncCallback(IAsyncResult ar);

C#

[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public delegate void AsyncCallback(IAsyncResult ar);

參數

ar

IAsyncResult

非同步作業的結果。

屬性

SerializableAttribute ComVisibleAttribute

範例

下列範例示範在 Dns 類別中使用非同步方法，以擷取使用者指定電腦的網域名稱系統 (DNS) 資訊。 此範例會建立參考ProcessDnsInformation方法的 AsyncCallback 委派。 此方法會呼叫每一個非同步要求一次以取得 DNS 資訊。

C#

/*
The following example demonstrates using asynchronous methods to
get Domain Name System information for the specified host computers.
This example uses a delegate to obtain the results of each asynchronous
operation.
*/

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

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class UseDelegateForAsyncCallback
    {
        static int requestCounter;
        static ArrayList hostData = new ArrayList();
        static StringCollection hostNames = new StringCollection();
        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);
                    // Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, host);
                 }
            } 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.
            for (int i = 0; i< hostNames.Count; i++)
            {
                object data = hostData [i];
                string message = data as string;
                // A SocketException was thrown.
                if (message != null)
                {
                    Console.WriteLine("Request for {0} returned message: {1}",
                        hostNames[i], message);
                    continue;
                }
                // Get the results.
                IPHostEntry h = (IPHostEntry) data;
                string[] aliases = h.Aliases;
                IPAddress[] addresses = h.AddressList;
                if (aliases.Length > 0)
                {
                    Console.WriteLine("Aliases for {0}", hostNames[i]);
                    for (int j = 0; j < aliases.Length; j++)
                    {
                        Console.WriteLine("{0}", aliases[j]);
                    }
                }
                if (addresses.Length > 0)
                {
                    Console.WriteLine("Addresses for {0}", hostNames[i]);
                    for (int k = 0; k < addresses.Length; k++)
                    {
                        Console.WriteLine("{0}",addresses[k].ToString());
                    }
                }
            }
       }

        // The following method is called when each asynchronous operation completes.
        static void ProcessDnsInformation(IAsyncResult result)
        {
            string hostName = (string) result.AsyncState;
            hostNames.Add(hostName);
            try
            {
                // Get the results.
                IPHostEntry host = Dns.EndGetHostEntry(result);
                hostData.Add(host);
            }
            // Store the exception message.
            catch (SocketException e)
            {
                hostData.Add(e.Message);
            }
            finally
            {
                // Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(ref requestCounter);
            }
        }
    }
}

備註

AsyncCallback使用委派在個別執行緒中處理非同步作業的結果。 委派 AsyncCallback 代表非同步作業完成時所呼叫的回呼方法。 回呼方法會採用 IAsyncResult 參數，其後續會用來取得非同步作業的結果。

如需非同步程式設計的詳細資訊，請參閱使用 AsyncCallback 委派結束非同步作業和使用事件架構非同步模式中的AsyncCallback 委派和狀態物件， (EAP) 。

擴充方法

GetMethodInfo(Delegate)

取得表示特定委派所代表之方法的物件。

適用於

另請參閱

• IAsyncResult
• 使用 AsyncCallback 委派結束非同步作業
• 使用 AsyncCallback 委派和狀態物件
• 以非同步的方式呼叫同步方法
• 事件架構非同步模式 (EAP)
• 處理和引發事件