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IAsyncResult Interface

Represents the status of an asynchronous operation.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Interface IAsyncResult

The IAsyncResult type exposes the following members.

  NameDescription
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsyncStateGets a user-defined object that qualifies or contains information about an asynchronous operation.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsyncWaitHandleGets a WaitHandle that is used to wait for an asynchronous operation to complete.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCompletedSynchronouslyGets a value that indicates whether the asynchronous operation completed synchronously.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsCompletedGets a value that indicates whether the asynchronous operation has completed.
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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 it is passed to 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.

NoteNote

The AsyncResult class is the implementation of IAsyncResult that is returned by the BeginInvoke method when you use a delegate to call a method asynchronously.

For a detailed description of how the IAsyncResult interface is used, see the Calling Synchronous Methods Asynchronously topic.

The following example demonstrates how to use the AsyncWaitHandle property to get a WaitHandle, and how to wait for an asynchronous call on a delegate. The WaitHandle is signaled when the asynchronous call completes, and you can wait for it by calling the WaitOne method.

The example consists of two classes: the class that contains the method that is called asynchronously, and the class that contains the Main method that makes the call.

For more information and more examples of calling methods asynchronously by using delegates, see Calling Synchronous Methods Asynchronously.

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


...


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.".

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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