Asynchronní volání synchronních metodCalling Synchronous Methods Asynchronously

Rozhraní .NET Framework umožňuje volat jakékoli metody asynchronně.The .NET Framework enables you to call any method asynchronously. Provedete to tak můžete definovat delegáta se stejným podpisem jako metodu, kterou chcete volat; modul common language runtime automaticky definuje BeginInvoke a EndInvoke metody pro tento delegát s odpovídajícími podpisy.To do this you define a delegate with the same signature as the method you want to call; the common language runtime automatically defines BeginInvoke and EndInvoke methods for this delegate, with the appropriate signatures.

Poznámka

Volání asynchronních delegátů, konkrétně BeginInvoke a EndInvoke metody, nejsou podporovány v rozhraní .NET Compact Framework.Asynchronous delegate calls, specifically the BeginInvoke and EndInvoke methods, are not supported in the .NET Compact Framework.

BeginInvoke Zahájí asynchronní volání metody.The BeginInvoke method initiates the asynchronous call. Má stejné parametry jako metodu, která je zapotřebí spustit asynchronně, a navíc další dva volitelné parametry.It has the same parameters as the method that you want to execute asynchronously, plus two additional optional parameters. První parametr je AsyncCallback delegáta, který odkazuje na metodu, která se má volat po dokončení asynchronního volání.The first parameter is an AsyncCallback delegate that references a method to be called when the asynchronous call completes. Druhý parametr je objekt definovaný uživatelem, který předává informace do metody zpětného volání.The second parameter is a user-defined object that passes information into the callback method. BeginInvoke Vrátí hodnotu okamžitě a nečeká na dokončení asynchronního volání.BeginInvoke returns immediately and does not wait for the asynchronous call to complete. BeginInvoke Vrátí IAsyncResult, které lze použít ke sledování průběhu asynchronní volání.BeginInvoke returns an IAsyncResult, which can be used to monitor the progress of the asynchronous call.

EndInvoke Načítá výsledek z asynchronního volání metody.The EndInvoke method retrieves the results of the asynchronous call. Může být volán kdykoli po BeginInvoke.It can be called any time after BeginInvoke. Pokud asynchronní volání nebyla dokončena, EndInvoke blokuje volající vlákno, dokud se nedokončí.If the asynchronous call has not completed, EndInvoke blocks the calling thread until it completes. Parametry EndInvoke zahrnout out a ref parametry (<Out> ByRef a ByRef v jazyce Visual Basic) metody, která je zapotřebí spustit asynchronně, plus IAsyncResult vrácený BeginInvoke.The parameters of EndInvoke include the out and ref parameters (<Out> ByRef and ByRef in Visual Basic) of the method that you want to execute asynchronously, plus the IAsyncResult returned by BeginInvoke.

Poznámka

Funkce IntelliSense v sadě Visual Studio zobrazuje parametry BeginInvoke a EndInvoke.The IntelliSense feature in Visual Studio displays the parameters of BeginInvoke and EndInvoke. Pokud nepoužíváte Visual Studio nebo něco podobného, nebo pokud používáte C# pomocí sady Visual Studio, naleznete v tématu asynchronního programovacího modelu (APM) popis o parametrech definovaných pro tyto metody.If you're not using Visual Studio or a similar tool, or if you're using C# with Visual Studio, see Asynchronous Programming Model (APM) for a description of the parameters defined for these methods.

Příklady kódu v tomto tématu ukazují čtyři běžné způsoby použití BeginInvoke a EndInvoke pro asynchronní volání.The code examples in this topic demonstrate four common ways to use BeginInvoke and EndInvoke to make asynchronous calls. Po volání BeginInvoke můžete dělat tyto věci:After calling BeginInvoke you can do the following:

  • Provést některé práci a následně zavolat EndInvoke do bloku, dokud se nedokončí volání.Do some work and then call EndInvoke to block until the call completes.

  • Získat WaitHandle pomocí IAsyncResult.AsyncWaitHandle vlastnosti, použijte jeho WaitOne metodu pro provádění bloku, dokud WaitHandle signalizován a pak vyvolejte EndInvoke.Obtain a WaitHandle using the IAsyncResult.AsyncWaitHandle property, use its WaitOne method to block execution until the WaitHandle is signaled, and then call EndInvoke.

  • Dotazování IAsyncResult vrácený BeginInvoke k určení po dokončení asynchronního volání a následně zavolat EndInvoke.Poll the IAsyncResult returned by BeginInvoke to determine when the asynchronous call has completed, and then call EndInvoke.

  • Předání delegáta pro metodu zpětného volání pro BeginInvoke.Pass a delegate for a callback method to BeginInvoke. Metoda se spouští podle ThreadPool vlákna po dokončení asynchronního volání.The method is executed on a ThreadPool thread when the asynchronous call completes. Volání metody zpětného volání EndInvoke.The callback method calls EndInvoke.

Důležité

Bez ohledu na to, které techniku použít, vždy volejte EndInvoke na dokončení asynchronního volání.No matter which technique you use, always call EndInvoke to complete your asynchronous call.

Definování testovací metody a asynchronních delegátůDefining the Test Method and Asynchronous Delegate

Následující příklady kódu ukazují různé způsoby volání stejné metody dlouhotrvající TestMethod, asynchronně.The code examples that follow demonstrate various ways of calling the same long-running method, TestMethod, asynchronously. TestMethod Metoda zobrazí zprávu konzoly, chcete-li zobrazit, že byl zahájen zpracování, po prodlevě pár sekund a končí.The TestMethod method displays a console message to show that it has begun processing, sleeps for a few seconds, and then ends. TestMethodout parametr předvést způsob, jak tyto parametry jsou přidány do signatur BeginInvoke a EndInvoke.TestMethod has an out parameter to demonstrate the way such parameters are added to the signatures of BeginInvoke and EndInvoke. Dokáže zpracovat ref parametry podobně.You can handle ref parameters similarly.

Následující příklad kódu ukazuje definici TestMethod a delegáta s názvem AsyncMethodCaller , který je možné volat TestMethod asynchronně.The following code example shows the definition of TestMethod and the delegate named AsyncMethodCaller that can be used to call TestMethod asynchronously. Chcete-li zkompilovat příklady kódu, musí obsahovat definice pro TestMethod a AsyncMethodCaller delegovat.To compile the code examples, you must include the definitions for TestMethod and the AsyncMethodCaller delegate.

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
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

Čekání na asynchronní volání s EndInvokeWaiting for an Asynchronous Call with EndInvoke

Nejjednodušší způsob, jak provést asynchronní metody je spustit provedení metody při volání delegáta BeginInvoke metody, některé pracovat na hlavním vlákně a následně zavolat delegáta EndInvoke metody.The simplest way to execute a method asynchronously is to start executing the method by calling the delegate's BeginInvoke method, do some work on the main thread, and then call the delegate's EndInvoke method. EndInvoke může blokovat volající vlákno, protože nevrací až po dokončení asynchronního volání.EndInvoke might block the calling thread because it does not return until the asynchronous call completes. Toto je dobrý postup pomocí souboru nebo síťové operace.This is a good technique to use with file or network operations.

Důležité

Protože EndInvoke může blokovat, které by nikdy neměl volat z vlákna uživatelského rozhraní služby.Because EndInvoke might block, you should never call it from threads that service the user interface.

#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

void main() 
{
    // The asynchronous method puts the thread id here.
    int threadId = 2546;

    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);
       
    // Initiate the asychronous call.
    IAsyncResult^ result = caller->BeginInvoke(3000, 
        threadId, nullptr, nullptr);

    Thread::Sleep(1);
    Console::WriteLine("Main thread {0} does some work.",
        Thread::CurrentThread->ManagedThreadId);

    // Call EndInvoke to wait for the asynchronous call to complete,
    // and to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, result);

    Console::WriteLine("The call executed on thread {0}, with return value \"{1}\".",
        threadId, returnValue);
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */
using System;
using System.Threading;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        public static void Main() 
        {
            // The asynchronous method puts the thread id here.
            int threadId;

            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);
       
            // Initiate the asychronous call.
            IAsyncResult result = caller.BeginInvoke(3000, 
                out threadId, null, null);

            Thread.Sleep(0);
            Console.WriteLine("Main thread {0} does some work.",
                Thread.CurrentThread.ManagedThreadId);

            // Call EndInvoke to wait for the asynchronous call to complete,
            // and to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, result);

            Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".",
                threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */
Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations
    Public Class AsyncMain 
        Shared Sub Main() 
            ' The asynchronous method puts the thread id here.
            Dim threadId As Integer

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)
       
            ' Initiate the asynchronous call.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                threadId, Nothing, Nothing)

            Thread.Sleep(0)
            Console.WriteLine("Main thread {0} does some work.", _
                 Thread.CurrentThread.ManagedThreadId)

            ' Call EndInvoke to Wait for the asynchronous call to complete,
            ' and to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, result)

            Console.WriteLine("The call executed on thread {0}, with return value ""{1}"".", _
                threadId, returnValue)
        End Sub
    End Class

End Namespace

'This example produces output similar to the following:
'
'Main thread 1 does some work.
'Test method begins.
'The call executed on thread 3, with return value "My call time was 3000.".

Čekání na asynchronní volání s WaitHandleWaiting for an Asynchronous Call with WaitHandle

Můžete získat WaitHandle pomocí AsyncWaitHandle vlastnost IAsyncResult vrácený BeginInvoke.You can obtain a WaitHandle by using the AsyncWaitHandle property of the IAsyncResult returned by BeginInvoke. WaitHandle Signalizován po dokončení asynchronního volání a může čekat na jeho voláním WaitOne metody.The WaitHandle is signaled when the asynchronous call completes, and you can wait for it by calling the WaitOne method.

Pokud používáte WaitHandle, můžete provést další zpracování před nebo po dokončení asynchronního volání, ale před voláním EndInvoke k načtení výsledků.If you use a WaitHandle, you can perform additional processing before or after the asynchronous call completes, but before calling EndInvoke to retrieve the results.

Poznámka

Popisovač čekání není uzavřená automaticky při volání EndInvoke.The wait handle is not closed automatically when you call EndInvoke. Pokud můžete uvolnit všechny odkazy na popisovač čekání, jsou uvolněny systémové prostředky při uvolňování paměti získá popisovač čekání.If you release all references to the wait handle, system resources are freed when garbage collection reclaims the wait handle. Uvolnit systémové prostředky, jakmile budete hotovi, pomocí popisovač čekání, vyřadit voláním WaitHandle.Close metody.To free the system resources as soon as you are finished using the wait handle, dispose of it by calling the WaitHandle.Close method. Uvolňování paměti funguje efektivněji, když se objekt explicitně uvolněn uvolnitelné objekty.Garbage collection works more efficiently when disposable objects are explicitly disposed.

#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

void main() 
{
    // The asynchronous method puts the thread id here.
    int threadId;

    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);
       
    // Initiate the asychronous call.
    IAsyncResult^ result = caller->BeginInvoke(3000, 
        threadId, nullptr, nullptr);

    Thread::Sleep(0);
    Console::WriteLine("Main thread {0} does some work.",
        Thread::CurrentThread->ManagedThreadId);

    // Wait for the WaitHandle to become signaled.
    result->AsyncWaitHandle->WaitOne();

    // Perform additional processing here.
    // Call EndInvoke to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, result);

    // Close the wait handle.
    result->AsyncWaitHandle->Close();

    Console::WriteLine("The call executed on thread {0}, with return value \"{1}\".",
        threadId, returnValue);
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */
using System;
using System.Threading;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        static void Main() 
        {
            // The asynchronous method puts the thread id here.
            int threadId;

            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);
       
            // Initiate the asychronous call.
            IAsyncResult result = caller.BeginInvoke(3000, 
                out threadId, null, null);

            Thread.Sleep(0);
            Console.WriteLine("Main thread {0} does some work.",
                Thread.CurrentThread.ManagedThreadId);

            // Wait for the WaitHandle to become signaled.
            result.AsyncWaitHandle.WaitOne();

            // Perform additional processing here.
            // Call EndInvoke to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, result);

            // Close the wait handle.
            result.AsyncWaitHandle.Close();

            Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".",
                threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */
Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class AsyncMain 
        Shared Sub Main() 
            ' The asynchronous method puts the thread id here.
            Dim threadId As Integer

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)
       
            ' Initiate the asynchronous call.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                threadId, Nothing, Nothing)

            Thread.Sleep(0)
            Console.WriteLine("Main thread {0} does some work.", _
                Thread.CurrentThread.ManagedThreadId)
            ' Perform additional processing here and then
            ' wait for the WaitHandle to be signaled.
            result.AsyncWaitHandle.WaitOne()

            ' Call EndInvoke to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, result)

            ' Close the wait handle.
            result.AsyncWaitHandle.Close()

            Console.WriteLine("The call executed on thread {0}, with return value ""{1}"".", _
                threadId, returnValue)
        End Sub
    End Class
End Namespace

'This example produces output similar to the following:
'
'Main thread 1 does some work.
'Test method begins.
'The call executed on thread 3, with return value "My call time was 3000.".

Dotazování na dokončení asynchronního voláníPolling for Asynchronous Call Completion

Můžete použít IsCompleted vlastnost IAsyncResult vrácený BeginInvoke ke zjišťování po dokončení asynchronního volání.You can use the IsCompleted property of the IAsyncResult returned by BeginInvoke to discover when the asynchronous call completes. Můžete tak učinit při provádění asynchronní volání z vlákna, které uživatelské rozhraní služby.You might do this when making the asynchronous call from a thread that services the user interface. Dotazování pro dokončení umožňuje volajícího vlákna má pokračovat provedením během asynchronního volání se spustí na ThreadPool vlákna.Polling for completion allows the calling thread to continue executing while the asynchronous call executes on a ThreadPool thread.

#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

void main() 
{
    // The asynchronous method puts the thread id here.
    int threadId;

    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);
       
    // Initiate the asychronous call.
    IAsyncResult^ result = caller->BeginInvoke(3000, 
        threadId, nullptr, nullptr);

    // Poll while simulating work.
    while(result->IsCompleted == false)
    {
        Thread::Sleep(250);
        Console::Write(".");
    }

    // Call EndInvoke to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, result);

    Console::WriteLine("\nThe call executed on thread {0}, with return value \"{1}\".",
        threadId, returnValue);
}

/* This example produces output similar to the following:

Test method begins.
.............
The call executed on thread 3, with return value "My call time was 3000.".
 */
using System;
using System.Threading;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        static void Main() {
            // The asynchronous method puts the thread id here.
            int threadId;

            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);
       
            // Initiate the asychronous call.
            IAsyncResult result = caller.BeginInvoke(3000, 
                out threadId, null, null);

            // Poll while simulating work.
            while(result.IsCompleted == false) {
                Thread.Sleep(250);
                Console.Write(".");
            }

            // Call EndInvoke to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, result);

            Console.WriteLine("\nThe call executed on thread {0}, with return value \"{1}\".",
                threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

Test method begins.
.............
The call executed on thread 3, with return value "My call time was 3000.".
 */
Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class AsyncMain 
        Shared Sub Main() 
            ' The asynchronous method puts the thread id here.
            Dim threadId As Integer

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)
       
            ' Initiate the asynchronous call.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                threadId, Nothing, Nothing)

            ' Poll while simulating work.
            While result.IsCompleted = False
                Thread.Sleep(250)
                Console.Write(".")
            End While

            ' Call EndInvoke to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, result)

            Console.WriteLine(vbCrLf & _
                "The call executed on thread {0}, with return value ""{1}"".", _
                threadId, returnValue)
        End Sub
    End Class
End Namespace

' This example produces output similar to the following:
'
'Test method begins.
'.............
'The call executed on thread 3, with return value "My call time was 3000.".

Provádění metody zpětného volání při dokončení asynchronní voláníExecuting a Callback Method When an Asynchronous Call Completes

Pokud podproces, který iniciuje asynchronní volání nemusí být vlákna, která zpracovává výsledky, je možné spustit metodu zpětného volání při dokončení volání.If the thread that initiates the asynchronous call does not need to be the thread that processes the results, you can execute a callback method when the call completes. Metoda zpětného volání, které se spouští podle ThreadPool vlákna.The callback method is executed on a ThreadPool thread.

Pokud chcete použít metodu zpětného volání, musíte předat BeginInvoke AsyncCallback delegáta, který představuje metodu zpětného volání.To use a callback method, you must pass BeginInvoke an AsyncCallback delegate that represents the callback method. Můžete také předat objekt, který obsahuje informace, které použije metoda zpětného volání.You can also pass an object that contains information to be used by the callback method. V metodě zpětného volání, můžete přetypovat IAsyncResult, na který je jediným parametrem metody zpětného volání AsyncResult objektu.In the callback method, you can cast the IAsyncResult, which is the only parameter of the callback method, to an AsyncResult object. Pak můžete použít AsyncResult.AsyncDelegate vlastnost k získání delegáta, který byl použit k iniciujte hovor, takže můžete volat EndInvoke.You can then use the AsyncResult.AsyncDelegate property to get the delegate that was used to initiate the call so that you can call EndInvoke.

Poznámky v tomto příkladu:Notes on the example:

  • threadId Parametr TestMethod je out parametr ([<Out> ByRef v jazyce Visual Basic), takže jeho vstupní hodnotu nikdy používají TestMethod.The threadId parameter of TestMethod is an out parameter ([<Out> ByRef in Visual Basic), so its input value is never used by TestMethod. Fiktivní proměnná je předána BeginInvoke volání.A dummy variable is passed to the BeginInvoke call. Pokud threadId byly parametr ref parametr (ByRef v jazyce Visual Basic), proměnné by mohl být pole třídu úrovně tak, aby ho mohli předat i BeginInvoke a EndInvoke.If the threadId parameter were a ref parameter (ByRef in Visual Basic), the variable would have to be a class-level field so that it could be passed to both BeginInvoke and EndInvoke.

  • Informace o stavu, který je předán BeginInvoke je formátovací řetězec, který používá metodu zpětného volání k formátování výstupní zprávu.The state information that is passed to BeginInvoke is a format string, which the callback method uses to format an output message. Protože je předán jako typ Object, informace o stavu musí být přetypovat na typ správné předtím, než je možné.Because it is passed as type Object, the state information must be cast to its proper type before it can be used.

  • Je provedeno zpětné volání ThreadPool vlákna.The callback is made on a ThreadPool thread. ThreadPool vlákna jsou vlákna na pozadí, které není byla aplikace spuštěná, pokud hlavní podproces skončí, takže do režimu spánku dostatečně dlouhou dobu na dokončení zpětného volání obsahuje hlavní vlákno v příkladu.ThreadPool threads are background threads, which do not keep the application running if the main thread ends, so the main thread of the example has to sleep long enough for the callback to finish.

#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
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.

Viz také:See also