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UdpClient.BeginReceive Method

.NET Framework 3.5

Receives a datagram from a remote host asynchronously.

Namespace:  System.Net.Sockets
Assembly:  System (in System.dll)
C#
C++
JScript
VB
Copy 
[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public IAsyncResult BeginReceive(
	AsyncCallback requestCallback,
	Object state
)

Parameters

requestCallback
Type: System.AsyncCallback
An AsyncCallback delegate that references the method to invoke when the operation is complete.
state
Type: System.Object
A user-defined object that contains information about the receive operation. This object is passed to the requestCallback delegate when the operation is complete.

Return Value

Type: System.IAsyncResult
An IAsyncResult object that references the asynchronous receive.
Note Note:

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The asynchronous BeginReceive operation must be completed by calling the EndReceive method. Typically, the method is invoked by the requestCallback delegate.

This method does not block until the operation is complete. To block until the operation is complete, use the Receive method.

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

The following code example uses BeginReceive to asynchronously receive a server response.

C#
C++
Copy 
public static bool messageReceived = false;

public static void ReceiveCallback(IAsyncResult ar)
{
  UdpClient u = (UdpClient)((UdpState)(ar.AsyncState)).u;
  IPEndPoint e = (IPEndPoint)((UdpState)(ar.AsyncState)).e;

  Byte[] receiveBytes = u.EndReceive(ar, ref e);
  string receiveString = Encoding.ASCII.GetString(receiveBytes);

  Console.WriteLine("Received: {0}", receiveString);
  messageReceived = true;
}

public static void ReceiveMessages()
{
  // Receive a message and write it to the console.
  IPEndPoint e = new IPEndPoint(IPAddress.Any, listenPort);
  UdpClient u = new UdpClient(e);

  UdpState s = new UdpState();
  s.e = e;
  s.u = u;

  Console.WriteLine("listening for messages");
  u.BeginReceive(new AsyncCallback(ReceiveCallback), s);

  // Do some work while we wait for a message. For this example,
  // we'll just sleep
  while (!messageReceived)
  {
    Thread.Sleep(100);
  }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

Supported in: 3.5, 3.0, 2.0
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Annotations FAQ
Related to the UdpState
Using the method BeginReceive included in the UdpClient class, I tried to follow the example given by msdn website in order to use it properly.
As I wasn't very familiar with this C# class I first copied the code to make it work but the code doesn't actually compile. The reason is the UdpState is not recognized, and so for the only reason that it is not a proper C# class.

For the incoming people who wants to use that method, you must create a class called UdpState containing an IPEndPoint and a UdpClient as below:

class UdpState
{
public IPEndPoint e;
public UdpClient u;
}

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