AsyncCallback デリゲートおよび状態オブジェクトの使用
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。 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。
例
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。 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。 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。 このオブジェクトは BeginGetHostByName メソッドに渡されます。 ProcessDnsInformation メソッドは、要求が完了するたびに呼び出されます。 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。 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。 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。
/*
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
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