Export (0) Print
Expand All

IAsyncResult Interface

Represents the status of an asynchronous operation.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Interface IAsyncResult
'Usage
Dim instance As 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 Shared Sub MyCallback(ar As IAsyncResult)
   ' Obtains the last parameter of the delegate call.
   Dim value As Integer = Convert.ToInt32(ar.AsyncState)
   
   ' Obtains return value from the delegate call using EndInvoke.
   Dim aResult As AsyncResult = CType(ar, AsyncResult)
   Dim temp As SampSyncSqrDelegate = CType(aResult.AsyncDelegate, SampSyncSqrDelegate)
   Dim result As Integer = temp.EndInvoke(ar)
   
   Console.Write("Simple.SomeMethod (AsyncCallback): Result of ")
   Console.WriteLine("{0} in SampleSynchronized.Square is {1} ", value, result)
End Sub 'MyCallback  

// 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.

Imports System
Imports System.Threading
Imports System.Runtime.Remoting
Imports System.Runtime.Remoting.Contexts
Imports System.Runtime.Remoting.Messaging


'
' Context-Bound type with Synchronization Context Attribute
'
<Synchronization()> Public Class SampleSyncronized
   Inherits ContextBoundObject
   
   ' A method that does some work - returns the square of the given number
   Public Function Square(i As Integer) As Integer
      Console.Write("SampleSyncronized.Square called.  ")
      Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode())
      Return i * i
   End Function 'Square
End Class 'SampleSyncronized



'
' Async delegate used to call a method with this signature asynchronously
'
Delegate Function SampSyncSqrDelegate(i As Integer) As Integer


'Main sample class
Public Class AsyncResultSample
   
   Public Shared Sub Main()
      Dim callParameter As Integer = 0
      Dim callResult As Integer = 0
      
      'Create an instance of a context-bound type SampleSynchronized
      'Because SampleSynchronized is context-bound, the object sampSyncObj 
      'is a transparent proxy
      Dim sampSyncObj As 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}.", callParameter, callResult)
      Console.WriteLine("")
      Console.WriteLine("")
      
      
      '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())
      Dim sampleDelegate As New SampSyncSqrDelegate(AddressOf sampSyncObj.Square)
      callParameter = 17
      
      Dim aResult As IAsyncResult = sampleDelegate.BeginInvoke(callParameter, Nothing, Nothing)
      
      '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)

   End Sub 'Main

End Class 'AsyncResultSample

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

Community Additions

ADD
Show:
© 2015 Microsoft