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MessageQueue.EndPeek Method

Completes the specified asynchronous peek operation.

[Visual Basic]
Public Function EndPeek( _
   ByVal asyncResult As IAsyncResult _
) As Message
[C#]
public Message EndPeek(
 IAsyncResult asyncResult
);
[C++]
public: Message* EndPeek(
 IAsyncResult* asyncResult
);
[JScript]
public function EndPeek(
   asyncResult : IAsyncResult
) : Message;

Parameters

asyncResult
The IAsyncResult that identifies the asynchronous peek operation to finish, and from which to retrieve an end result.

Return Value

The Message associated with the completed asynchronous operation.

Exceptions

Exception Type Condition
ArgumentNullException The asyncResult parameter is a null reference (Nothing in Visual Basic).
ArgumentException The syntax of the asyncResult parameter is invalid.
MessageQueueException An error occurred when accessing a Message Queuing API.

Remarks

When the PeekCompleted event is raised, EndPeek completes the operation that was initiated by the BeginPeek call. To do so, EndPeek peeks the message.

BeginPeek can specify a time-out, which causes the PeekCompleted event to be raised if the time-out occurs before a message appears in the queue. In this case, the IsCompleted property of the asyncResult parameter is set to true, but no message is associated with the operation. When a time-out occurs without a message arriving in the queue, a subsequent call to EndPeek throws an exception.

EndPeek is used to read the message that caused the PeekCompleted event to be raised.

If you want to continue to asynchronously peek messages, you can again call BeginPeek after calling EndPeek.

The following table shows whether this method is available in various Workgroup modes.

Workgroup Mode Available
Local computer Yes
Local computer + direct format name Yes
Remote computer No
Remote computer + direct format name Yes

Example

[Visual Basic, C#, C++] The following example creates an event handler named MyPeekCompleted, attaches it to the PeekCompleted event handler delegate, and calls BeginPeek to initiate an asynchronous peek operation on the queue that is located at the path ".\myQueue". When a PeekCompleted event is raised, the example peeks the message and writes its body to the screen. The example then calls BeginPeek again to initiate a new asynchronous peek operation.

[Visual Basic] 
Imports System
Imports System.Messaging


Namespace MyProject

    '/ <summary>
    '/ Provides a container class for the example.
    '/ </summary>
    Public Class MyNewQueue


        '**************************************************
        ' Provides an entry point into the application.
        '         
        ' This example performs asynchronous peek operation
        ' processing.
        '**************************************************

        Public Shared Sub Main()
            ' Create an instance of MessageQueue. Set its formatter.
            Dim myQueue As New MessageQueue(".\myQueue")
            myQueue.Formatter = New XmlMessageFormatter(New Type() _
                {GetType([String])})

            ' Add an event handler for the PeekCompleted event.
            AddHandler myQueue.PeekCompleted, AddressOf _
                MyPeekCompleted

            ' Begin the asynchronous peek operation.
            myQueue.BeginPeek()

            ' Do other work on the current thread.
            Return
        End Sub 'Main


        '**************************************************
        ' Provides an event handler for the PeekCompleted
        ' event.
        '**************************************************

        Private Shared Sub MyPeekCompleted(ByVal [source] As _
            [Object], ByVal asyncResult As PeekCompletedEventArgs)

            ' Connect to the queue.
            Dim mq As MessageQueue = CType([source], MessageQueue)

            ' End the asynchronous peek operation.
            Dim m As Message = mq.EndPeek(asyncResult.AsyncResult)

            ' Display message information on the screen.
            Console.WriteLine(("Message: " + CStr(m.Body)))

            ' Restart the asynchronous peek operation.
            mq.BeginPeek()

            Return

        End Sub 'MyPeekCompleted

    End Class 'MyNewQueue
End Namespace 'MyProject

[C#] 
using System;
using System.Messaging;

namespace MyProject
{
    /// <summary>
    /// Provides a container class for the example.
    /// </summary>
    public class MyNewQueue
    {

        //**************************************************
        // Provides an entry point into the application.
        //         
        // This example performs asynchronous peek operation
        // processing.
        //**************************************************

        public static void Main()
        {
            // Create an instance of MessageQueue. Set its formatter.
            MessageQueue myQueue = new MessageQueue(".\\myQueue");
            myQueue.Formatter = new XmlMessageFormatter(new Type[]
                {typeof(String)});

            // Add an event handler for the PeekCompleted event.
            myQueue.PeekCompleted += new 
                PeekCompletedEventHandler(MyPeekCompleted);
            
            // Begin the asynchronous peek operation.
            myQueue.BeginPeek();
            
            // Do other work on the current thread.

            return;
        }


        //**************************************************
        // Provides an event handler for the PeekCompleted
        // event.
        //**************************************************
        
        private static void MyPeekCompleted(Object source, 
            PeekCompletedEventArgs asyncResult)
        {
            // Connect to the queue.
            MessageQueue mq = (MessageQueue)source;

            // End the asynchronous peek operation.
            Message m = mq.EndPeek(asyncResult.AsyncResult);

            // Display message information on the screen.
            Console.WriteLine("Message: " + (string)m.Body);

            // Restart the asynchronous peek operation.
            mq.BeginPeek();
            
            return; 
        }
    }
}

[C++] 
#using <mscorlib.dll>
#using <system.dll>
#using <system.messaging.dll>

using namespace System;
using namespace System::Messaging;

// This example performs asynchronous peek operation
// processing.
//*************************************************

__gc class MyNewQueue 
{
// Provides an event handler for the PeekCompleted
// event.
public:
    static void MyPeekCompleted(Object* source, PeekCompletedEventArgs* asyncResult) 
    {
        // Connect to the queue.
        MessageQueue* mq = dynamic_cast<MessageQueue*>(source);

        // End the asynchronous peek operation.
        Message* m = mq->EndPeek(asyncResult->AsyncResult);

        // Display message information on the screen.
        Console::WriteLine(S"Message: {0}", static_cast<String*>(m->Body));

        // Restart the asynchronous peek operation.
        mq->BeginPeek();

        return; 
    }
};

// Provides an entry point into the application.
//         

int main() 
{
    // Create an instance of MessageQueue. Set its formatter.
    MessageQueue* myQueue = new MessageQueue(S".\\myQueue");

    Type* p __gc[] = new Type* __gc[1];
    p[0] = __typeof(String);
    myQueue->Formatter = new XmlMessageFormatter( p );

    // Add an event handler for the PeekCompleted event.
    myQueue->PeekCompleted += new PeekCompletedEventHandler(0, MyNewQueue::MyPeekCompleted);

    // Begin the asynchronous peek operation.
    myQueue->BeginPeek();

    // Do other work on the current thread.

    return 0;
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

.NET Framework Security: 

See Also

MessageQueue Class | MessageQueue Members | System.Messaging Namespace | BeginPeek | PeekCompleted | EndReceive

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