AsyncCallback Delegát
Definice
Důležité
Některé informace platí pro předběžně vydaný produkt, který se může zásadně změnit, než ho výrobce nebo autor vydá. Microsoft neposkytuje žádné záruky, výslovné ani předpokládané, týkající se zde uváděných informací.
Odkazuje na metodu, která se má volat při dokončení odpovídající asynchronní operace.
public delegate void AsyncCallback(IAsyncResult ^ ar);public delegate void AsyncCallback(IAsyncResult ar);[System.Serializable]
public delegate void AsyncCallback(IAsyncResult ar);[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public delegate void AsyncCallback(IAsyncResult ar);type AsyncCallback = delegate of IAsyncResult -> unit[<System.Serializable>]
type AsyncCallback = delegate of IAsyncResult -> unit[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type AsyncCallback = delegate of IAsyncResult -> unitPublic Delegate Sub AsyncCallback(ar As IAsyncResult)Parametry
- ar
- IAsyncResult
Výsledek asynchronní operace.
- Atributy
Příklady
Následující příklad kódu ukazuje použití asynchronních metod ve Dns třídě k načtení informací DNS (Domain Name System) pro počítače zadané uživatelem. Tento příklad vytvoří delegáta AsyncCallback , který odkazuje na metodu ProcessDnsInformation . Tato metoda se volá jednou pro každý asynchronní požadavek na informace DNS.
/*
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);
}
}
}
}
// 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.
open System
open System.Net
open System.Net.Sockets
open System.Threading
open System.Collections.Specialized
let mutable requestCounter = 0
let hostData = ResizeArray<Result<IPHostEntry, string>>()
let hostNames = StringCollection()
let updateUserInterface () =
// Print a message to indicate that the application
// is still working on the remaining requests.
printfn $"{requestCounter} requests remaining."
// The following function is called when each asynchronous operation completes.
let processDnsInformation (result: IAsyncResult) =
string result.AsyncState
|> hostNames.Add
|> ignore
try
try
// Get the results.
Dns.EndGetHostEntry result
|> Ok
|> hostData.Add
// Store the exception message.
with :? SocketException as e ->
Error e.Message
|> hostData.Add
finally
// Decrement the request counter in a thread-safe manner.
Interlocked.Decrement &requestCounter
|> ignore
// Create the delegate that will process the results of the asynchronous request.
let callBack = AsyncCallback processDnsInformation
let mutable host = " "
while host.Length > 0 do
printf " Enter the name of a host computer or <enter> to finish: "
host <- stdin.ReadLine()
if host.Length > 0 then
// Increment the request counter in a thread safe manner.
Interlocked.Increment &requestCounter |> ignore
// Start the asynchronous request for DNS information.
Dns.BeginGetHostEntry(host, callBack, host) |> ignore
// The user has entered all of the host names for lookup.
// Now wait until the threads complete.
while requestCounter > 0 do
updateUserInterface ()
// Display the results.
for i = 0 to hostNames.Count - 1 do
match hostData[i] with
| Error message ->
// A SocketException was thrown.
printfn $"Request for {hostNames[i]} returned message: {message}"
| Ok entry ->
// Get the results.
let aliases = entry.Aliases
let addresses = entry.AddressList
if aliases.Length > 0 then
printfn $"Aliases for {hostNames[i]}"
for alias in aliases do
printfn $"{alias}"
if addresses.Length > 0 then
printfn $"Addresses for {hostNames[i]}"
for address in addresses do
printfn $"{address}"
'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.
Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Collections.Specialized
Imports System.Collections
Namespace Examples.AdvancedProgramming.AsynchronousOperations
Public Class UseDelegateForAsyncCallback
Dim Shared requestCounter as Integer
Dim Shared hostData as ArrayList = new ArrayList()
Dim Shared hostNames as StringCollection = new StringCollection()
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
Dim host as string
Dim i, j, k as Integer
callback = AddressOf ProcessDnsInformation
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)
' Start the asynchronous request for DNS information.
Dns.BeginGetHostEntry(host, callBack, host)
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 i = 0 To hostNames.Count -1
Dim dataObject as Object = hostData (i)
Dim message as String
' Was a SocketException was thrown?
If TypeOf dataObject is String
message = CType(dataObject, String)
Console.WriteLine("Request for {0} returned message: {1}", _
hostNames(i), message)
Else
' Get the results.
Dim h as IPHostEntry = CType(dataObject, IPHostEntry)
Dim aliases() as String = h.Aliases
Dim addresses() as IPAddress = h.AddressList
If aliases.Length > 0
Console.WriteLine("Aliases for 0}", hostNames(i))
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}", hostNames(i))
For k = 0 To addresses.Length -1
Console.WriteLine("{0}",addresses(k).ToString())
Next k
End If
End If
Next i
End Sub
' The following method is called when each asynchronous operation completes.
Shared Sub ProcessDnsInformation(result as IAsyncResult)
Dim hostName as String = CType(result.AsyncState, String)
hostNames.Add(hostName)
Try
' Get the results.
Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
hostData.Add(host)
' Store the exception message.
Catch e as SocketException
hostData.Add(e.Message)
Finally
' Decrement the request counter in a thread-safe manner.
Interlocked.Decrement(requestCounter)
End Try
End Sub
End Class
End Namespace
Poznámky
Pomocí delegáta AsyncCallback můžete zpracovat výsledky asynchronní operace v samostatném vlákně. Delegát AsyncCallback představuje metodu zpětného volání, která je volána po dokončení asynchronní operace. Metoda zpětného IAsyncResult volání přebírá parametr, který se následně použije k získání výsledků asynchronní operace.
Další informace o asynchronním programování najdete v tématech Použití delegáta AsyncCallback k ukončení asynchronní operace a Použití delegáta AsyncCallback a objektu stavu v asynchronním vzoru založeném na událostech (EAP).
Metody rozšíření
| GetMethodInfo(Delegate) |
Získá objekt, který představuje metodu reprezentovanou zadaným delegátem. |