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IAsyncResult Interface

Represents the status of an asynchronous operation.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

[ComVisibleAttribute(true)] 
public interface IAsyncResult
/** @attribute ComVisibleAttribute(true) */ 
public interface IAsyncResult
ComVisibleAttribute(true) 
public interface IAsyncResult
Not applicable.

The IAsyncResult interface is implemented by classes containing methods that can operate asynchronously. It is the return type of methods that initiate an asynchronous operation, such as FileStream.BeginRead, and is the type of the third parameter of methods that conclude an asynchronous operation, such as FileStream.EndRead. IAsyncResult objects are also passed to methods invoked by AsyncCallback delegates when an asynchronous operation completes.

An object that supports the IAsyncResult interface stores state information for an asynchronous operation, and provides a synchronization object to allow threads to be signaled when the operation completes.

For a detailed description of how the IAsyncResult interface is used, see the Asynchronous Programming Overview topic.

The following sample demonstrates using an IAsyncResult to obtain the return value of an asynchronous operation.

// Asynchronous Callback method.
public static void MyCallback(IAsyncResult ar) {

    // Obtains the last parameter of the delegate call.
    int value = Convert.ToInt32(ar.AsyncState);

    // Obtains return value from the delegate call using EndInvoke.
    AsyncResult aResult = (AsyncResult)ar;
    SampSyncSqrDelegate temp = (SampSyncSqrDelegate)aResult.AsyncDelegate;
    int result = temp.EndInvoke(ar);

    Console.Write("Simple.SomeMethod (AsyncCallback): Result of ");
    Console.WriteLine("{0} in SampleSynchronized.Square is {1} ", value, result);
}

// Asynchronous Callback method.
public static void MyCallback(IAsyncResult ar)
{
    // Obtains the last parameter of the delegate call.
    SampSyncSqrDelegate sampDelg = (SampSyncSqrDelegate)ar.get_AsyncState();
    
    // Obtains return value from the delegate call using EndInvoke.
    AsyncResult aResult = (AsyncResult)ar;
    SampSyncSqrDelegate temp =
        (SampSyncSqrDelegate)(aResult.get_AsyncDelegate());
    int threadId = AppDomain.GetCurrentThreadId();
    int result = temp.EndInvoke(ar);

    Console.Write("Simple.SomeMethod (AsyncCallback): Result of ");
    Console.WriteLine("{0} in SampleSynchronized.Square is {1} ",
        (Int32)value, (Int32)result);
} //MyCallback

The following sample demonstrates waiting for an asynchronous operation to complete.

using System;
using System.Threading;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Contexts;
using System.Runtime.Remoting.Messaging;

//
// Context-Bound type with Synchronization Context Attribute
//
[Synchronization()]
public class SampleSyncronized : ContextBoundObject
{
    // A method that does some work - returns the square of the given number
    public int Square(int i)
    {
        Console.Write("SampleSyncronized.Square called.  ");
        Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode());
        return i*i;
    }
}


//
// Async delegate used to call a method with this signature asynchronously
//
public delegate int SampSyncSqrDelegate(int i);

//Main sample class
public class AsyncResultSample
{
    public static void Main()
    {
        int callParameter = 0;
        int callResult = 0;

        //Create an instance of a context-bound type SampleSynchronized
        //Because SampleSynchronized is context-bound, the object sampSyncObj 
        //is a transparent proxy
        SampleSyncronized sampSyncObj = new SampleSyncronized();


        //call the method synchronously
        Console.Write("Making a synchronous call on the object.  ");
        Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode());
        callParameter = 10;
        callResult = sampSyncObj.Square(callParameter);
        Console.WriteLine("Result of calling sampSyncObj.Square with {0} is {1}.\n\n", callParameter, callResult);


        //call the method asynchronously
        Console.Write("Making an asynchronous call on the object.  ");
        Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode());
        SampSyncSqrDelegate sampleDelegate = new SampSyncSqrDelegate(sampSyncObj.Square);
        callParameter = 17;

        IAsyncResult aResult = sampleDelegate.BeginInvoke(callParameter, null, null);

        //Wait for the call to complete
        aResult.AsyncWaitHandle.WaitOne();

        callResult = sampleDelegate.EndInvoke(aResult);
        Console.WriteLine("Result of calling sampSyncObj.Square with {0} is {1}.", callParameter, callResult);
    }
}

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0
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