TcpListener.BeginAcceptTcpClient Method (AsyncCallback, Object)


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Begins an asynchronous operation to accept an incoming connection attempt.

Namespace:   System.Net.Sockets
Assembly:  System (in System.dll)

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)>
Public Function BeginAcceptTcpClient (
	callback As AsyncCallback,
	state As Object
) As IAsyncResult


Type: System.AsyncCallback

An AsyncCallback delegate that references the method to invoke when the operation is complete.

Type: System.Object

A user-defined object containing information about the accept operation. This object is passed to the callback delegate when the operation is complete.

Return Value

Type: System.IAsyncResult

An IAsyncResult that references the asynchronous creation of the TcpClient.

Exception Condition

An error occurred while attempting to access the socket. See the Remarks section for more information.


The Socket has been closed.

The asynchronous BeginAcceptTcpClient operation must be completed by calling the EndAcceptTcpClient method. Typically, the method is invoked by the callback delegate.

This method does not block until the operation completes. To block until the operation completes, use the AcceptTcpClient method.

For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.


If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code and refer to the Windows Sockets version 2 API error code documentation in the MSDN library at for a detailed description of the error.


This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.

The following code example demonstrates the use of the BeginAcceptTcpClient method to create and connect a socket. The callback delegate calls the EndAcceptTcpClient method to end the asynchronous request.

' Thread signal.
Public Shared tcpClientConnected As New ManualResetEvent(False)

' Accept one client connection asynchronously.
Public Shared Sub DoBeginAcceptTcpClient(listener As TcpListener)
   ' Set the event to nonsignaled state.

   ' Start to listen for connections from a client.
   Console.WriteLine("Waiting for a connection...")

   ' Accept the connection. 
   ' BeginAcceptSocket() creates the accepted socket.
   listener.BeginAcceptTcpClient(New AsyncCallback(AddressOf DoAcceptTcpClientCallback), listener)

   ' Wait until a connection is made and processed before 
   ' continuing.
End Sub 'DoBeginAcceptTcpClient

' Process the client connection.
Public Shared Sub DoAcceptTcpClientCallback(ar As IAsyncResult)
   ' Get the listener that handles the client request.
   Dim listener As TcpListener = CType(ar.AsyncState, TcpListener)

   ' End the operation and display the received data on 
   ' the console.
   Dim client As TcpClient = listener.EndAcceptTcpClient(ar)

   ' Process the connection here. (Add the client to a
   ' server table, read data, etc.)
   Console.WriteLine("Client connected completed")

   ' Signal the calling thread to continue.
End Sub 'DoAcceptTcpClientCallback

.NET Framework
Available since 2.0
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