AsyncCallback デリゲートおよび状態オブジェクトの使用Using an AsyncCallback Delegate and State Object

AsyncCallback デリゲートを使用し、別個のスレッドで非同期操作の結果を処理するとき、状態オブジェクトを使用してコールバック間で情報を渡し、最終的な結果を取得できます。When you use an AsyncCallback delegate to process the results of the asynchronous operation in a separate thread, you can use a state object to pass information between the callbacks and to retrieve a final result. このトピックでは、「AsyncCallback デリゲートの使用による非同期操作の終了」の例をさらに展開することでそれを実践します。This topic demonstrates that practice by expanding the example in Using an AsyncCallback Delegate to End an Asynchronous Operation.

Example

次のコード例は、ユーザー指定のコンピューターのドメイン ネーム システム (DNS) 情報を取得するために、Dns クラスの非同期メソッドを使用してデモを実行します。The following code example demonstrates using asynchronous methods in the Dns class to retrieve Domain Name System (DNS) information for user-specified computers. この例では、HostRequest クラスを定義して使用し、状態情報を格納します。This example defines and uses the HostRequest class to store state information. HostRequest オブジェクトは、ユーザーがコンピューター名を入力するたびに作成されます。A HostRequest object gets created for each computer name entered by the user. このオブジェクトは BeginGetHostByName メソッドに渡されます。This object is passed to the BeginGetHostByName method. ProcessDnsInformation メソッドは、要求が完了するたびに呼び出されます。The ProcessDnsInformation method is called each time a request completes. HostRequest オブジェクトは AsyncState プロパティを利用して取得されます。The HostRequest object is retrieved using the AsyncState property. ProcessDnsInformation メソッドは HostRequest オブジェクトを使用し、要求により返された IPHostEntry か、スローされた SocketException を格納します。The ProcessDnsInformation method uses the HostRequest object to store the IPHostEntry returned by the request or a SocketException thrown by the request. 要求がすべて完了すると、アプリケーションは HostRequest オブジェクトを反復処理し、DNS 情報か SocketException エラー メッセージを表示します。When all requests are complete, the application iterates over the HostRequest objects and displays the DNS information or SocketException error message.

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

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

関連項目See also