IAsyncResult.AsyncState Eigenschaft
Definition
Wichtig
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Ruft ein benutzerdefiniertes Objekt ab, das einen asynchronen Vorgang qualifiziert oder Informationen darüber enthält.
public:
property System::Object ^ AsyncState { System::Object ^ get(); };public object AsyncState { get; }public object? AsyncState { get; }member this.AsyncState : objPublic ReadOnly Property AsyncState As ObjectEigenschaftswert
Ein benutzerdefiniertes Objekt, das einen asynchronen Vorgang qualifiziert oder Informationen darüber enthält.
Beispiele
Im folgenden Codebeispiel wird veranschaulicht, wie die AsyncState Eigenschaft verwendet wird, um Informationen an eine Rückrufmethode zu übergeben. Der letzte Parameter des BeginInvoke Methodenaufrufs ist eine Formatzeichenfolge, mit der die Rückrufmethode verwendet wird, um eine Ausgabemeldung zu formatieren.
Das Beispiel besteht aus zwei Klassen: die Klasse, die die Methode enthält, die asynchron aufgerufen wird, und die Klasse, die die Main Methode enthält, die den Aufruf vornimmt.
Weitere Informationen dazu, wie dieses Rückrufbeispiel funktioniert, und weitere Beispiele für Aufrufmethoden asynchron mithilfe von Stellvertretungen finden Sie unter Aufrufen synchroner Methoden asynchron.
using namespace System;
using namespace System::Threading;
using namespace System::Runtime::InteropServices;
namespace Examples {
namespace AdvancedProgramming {
namespace AsynchronousOperations
{
public ref class AsyncDemo
{
public:
// The method to be executed asynchronously.
String^ TestMethod(int callDuration, [OutAttribute] int% threadId)
{
Console::WriteLine("Test method begins.");
Thread::Sleep(callDuration);
threadId = Thread::CurrentThread->ManagedThreadId;
return String::Format("My call time was {0}.", callDuration);
}
};
// The delegate must have the same signature as the method
// it will call asynchronously.
public delegate String^ AsyncMethodCaller(int callDuration, [OutAttribute] int% threadId);
}}}
using System;
using System.Threading;
namespace Examples.AdvancedProgramming.AsynchronousOperations
{
public class AsyncDemo
{
// The method to be executed asynchronously.
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = Thread.CurrentThread.ManagedThreadId;
return String.Format("My call time was {0}.", callDuration.ToString());
}
}
// The delegate must have the same signature as the method
// it will call asynchronously.
public delegate string AsyncMethodCaller(int callDuration, out int threadId);
}
Imports System.Threading
Imports System.Runtime.InteropServices
Namespace Examples.AdvancedProgramming.AsynchronousOperations
Public Class AsyncDemo
' The method to be executed asynchronously.
Public Function TestMethod(ByVal callDuration As Integer, _
<Out> ByRef threadId As Integer) As String
Console.WriteLine("Test method begins.")
Thread.Sleep(callDuration)
threadId = Thread.CurrentThread.ManagedThreadId()
return String.Format("My call time was {0}.", callDuration.ToString())
End Function
End Class
' The delegate must have the same signature as the method
' it will call asynchronously.
Public Delegate Function AsyncMethodCaller(ByVal callDuration As Integer, _
<Out> ByRef threadId As Integer) As String
End Namespace
#using <TestMethod.dll>
using namespace System;
using namespace System::Threading;
using namespace System::Runtime::Remoting::Messaging;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;
// The callback method must have the same signature as the
// AsyncCallback delegate.
void CallbackMethod(IAsyncResult^ ar)
{
// Retrieve the delegate.
AsyncResult^ result = (AsyncResult^) ar;
AsyncMethodCaller^ caller = (AsyncMethodCaller^) result->AsyncDelegate;
// Retrieve the format string that was passed as state
// information.
String^ formatString = (String^) ar->AsyncState;
// Define a variable to receive the value of the out parameter.
// If the parameter were ref rather than out then it would have to
// be a class-level field so it could also be passed to BeginInvoke.
int threadId = 0;
// Call EndInvoke to retrieve the results.
String^ returnValue = caller->EndInvoke(threadId, ar);
// Use the format string to format the output message.
Console::WriteLine(formatString, threadId, returnValue);
};
void main()
{
// Create an instance of the test class.
AsyncDemo^ ad = gcnew AsyncDemo();
// Create the delegate.
AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);
// The threadId parameter of TestMethod is an out parameter, so
// its input value is never used by TestMethod. Therefore, a dummy
// variable can be passed to the BeginInvoke call. If the threadId
// parameter were a ref parameter, it would have to be a class-
// level field so that it could be passed to both BeginInvoke and
// EndInvoke.
int dummy = 0;
// Initiate the asynchronous call, passing three seconds (3000 ms)
// for the callDuration parameter of TestMethod; a dummy variable
// for the out parameter (threadId); the callback delegate; and
// state information that can be retrieved by the callback method.
// In this case, the state information is a string that can be used
// to format a console message.
IAsyncResult^ result = caller->BeginInvoke(3000,
dummy,
gcnew AsyncCallback(&CallbackMethod),
"The call executed on thread {0}, with return value \"{1}\".");
Console::WriteLine("The main thread {0} continues to execute...",
Thread::CurrentThread->ManagedThreadId);
// The callback is made on a ThreadPool thread. ThreadPool threads
// are background threads, which do not keep the application running
// if the main thread ends. Comment out the next line to demonstrate
// this.
Thread::Sleep(4000);
Console::WriteLine("The main thread ends.");
}
/* This example produces output similar to the following:
The main thread 1 continues to execute...
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
The main thread ends.
*/
using System;
using System.Threading;
using System.Runtime.Remoting.Messaging;
namespace Examples.AdvancedProgramming.AsynchronousOperations
{
public class AsyncMain
{
static void Main()
{
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);
// The threadId parameter of TestMethod is an out parameter, so
// its input value is never used by TestMethod. Therefore, a dummy
// variable can be passed to the BeginInvoke call. If the threadId
// parameter were a ref parameter, it would have to be a class-
// level field so that it could be passed to both BeginInvoke and
// EndInvoke.
int dummy = 0;
// Initiate the asynchronous call, passing three seconds (3000 ms)
// for the callDuration parameter of TestMethod; a dummy variable
// for the out parameter (threadId); the callback delegate; and
// state information that can be retrieved by the callback method.
// In this case, the state information is a string that can be used
// to format a console message.
IAsyncResult result = caller.BeginInvoke(3000,
out dummy,
new AsyncCallback(CallbackMethod),
"The call executed on thread {0}, with return value \"{1}\".");
Console.WriteLine("The main thread {0} continues to execute...",
Thread.CurrentThread.ManagedThreadId);
// The callback is made on a ThreadPool thread. ThreadPool threads
// are background threads, which do not keep the application running
// if the main thread ends. Comment out the next line to demonstrate
// this.
Thread.Sleep(4000);
Console.WriteLine("The main thread ends.");
}
// The callback method must have the same signature as the
// AsyncCallback delegate.
static void CallbackMethod(IAsyncResult ar)
{
// Retrieve the delegate.
AsyncResult result = (AsyncResult) ar;
AsyncMethodCaller caller = (AsyncMethodCaller) result.AsyncDelegate;
// Retrieve the format string that was passed as state
// information.
string formatString = (string) ar.AsyncState;
// Define a variable to receive the value of the out parameter.
// If the parameter were ref rather than out then it would have to
// be a class-level field so it could also be passed to BeginInvoke.
int threadId = 0;
// Call EndInvoke to retrieve the results.
string returnValue = caller.EndInvoke(out threadId, ar);
// Use the format string to format the output message.
Console.WriteLine(formatString, threadId, returnValue);
}
}
}
/* This example produces output similar to the following:
The main thread 1 continues to execute...
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
The main thread ends.
*/
Imports System.Threading
Imports System.Runtime.Remoting.Messaging
Namespace Examples.AdvancedProgramming.AsynchronousOperations
Public Class AsyncMain
Shared Sub Main()
' Create an instance of the test class.
Dim ad As New AsyncDemo()
' Create the delegate.
Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)
' The threadId parameter of TestMethod is an <Out> parameter, so
' its input value is never used by TestMethod. Therefore, a dummy
' variable can be passed to the BeginInvoke call. If the threadId
' parameter were a ByRef parameter, it would have to be a class-
' level field so that it could be passed to both BeginInvoke and
' EndInvoke.
Dim dummy As Integer = 0
' Initiate the asynchronous call, passing three seconds (3000 ms)
' for the callDuration parameter of TestMethod; a dummy variable
' for the <Out> parameter (threadId); the callback delegate; and
' state information that can be retrieved by the callback method.
' In this case, the state information is a string that can be used
' to format a console message.
Dim result As IAsyncResult = caller.BeginInvoke(3000, _
dummy, _
AddressOf CallbackMethod, _
"The call executed on thread {0}, with return value ""{1}"".")
Console.WriteLine("The main thread {0} continues to execute...", _
Thread.CurrentThread.ManagedThreadId)
' The callback is made on a ThreadPool thread. ThreadPool threads
' are background threads, which do not keep the application running
' if the main thread ends. Comment out the next line to demonstrate
' this.
Thread.Sleep(4000)
Console.WriteLine("The main thread ends.")
End Sub
' The callback method must have the same signature as the
' AsyncCallback delegate.
Shared Sub CallbackMethod(ByVal ar As IAsyncResult)
' Retrieve the delegate.
Dim result As AsyncResult = CType(ar, AsyncResult)
Dim caller As AsyncMethodCaller = CType(result.AsyncDelegate, AsyncMethodCaller)
' Retrieve the format string that was passed as state
' information.
Dim formatString As String = CType(ar.AsyncState, String)
' Define a variable to receive the value of the <Out> parameter.
' If the parameter were ByRef rather than <Out> then it would have to
' be a class-level field so it could also be passed to BeginInvoke.
Dim threadId As Integer = 0
' Call EndInvoke to retrieve the results.
Dim returnValue As String = caller.EndInvoke(threadId, ar)
' Use the format string to format the output message.
Console.WriteLine(formatString, threadId, returnValue)
End Sub
End Class
End Namespace
' This example produces output similar to the following:
'
'The main thread 1 continues to execute...
'Test method begins.
'The call executed on thread 3, with return value "My call time was 3000.".
'The main thread ends.
Hinweise
Diese Eigenschaft gibt das Objekt zurück, das der letzte Parameter der Methode ist, die einen asynchronen Vorgang initiiert.
Hinweise für Ausführende
Implementieren Sie diese Eigenschaft, damit der Aufrufer eines asynchronen Vorgangs ein anwendungsdefiniertes Objekt abrufen kann, das am Anfang des Vorgangs angegeben ist.
Hinweise für Aufrufer
Dieses Objekt kann verwendet werden, um Statusinformationen für den asynchronen Vorgang an einen AsyncCallback von Ihnen bereitgestellten Vorgang zu übergeben.