UdpClient.BeginSend Method (Byte[], Int32, String, Int32, AsyncCallback, Object)

Sends a datagram to a destination asynchronously. The destination is specified by the host name and port number.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public IAsyncResult BeginSend(
	byte[] datagram,
	int bytes,
	string hostname,
	int port,
	AsyncCallback requestCallback,
	Object state


Type: System.Byte[]

A Byte array that contains the data to be sent.

Type: System.Int32

The number of bytes to send.

Type: System.String

The destination host.

Type: System.Int32

The destination port number.

Type: System.AsyncCallback

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

Type: System.Object

A user-defined object that contains information about the send 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 send.

The asynchronous BeginSend operation must be completed by calling the EndSend 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 one of the Send method overloads.

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


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 following code example uses BeginSend to asynchronously send a server request.

public static bool messageSent = false;

public static void SendCallback(IAsyncResult ar)
  UdpClient u = (UdpClient)ar.AsyncState;

  Console.WriteLine("number of bytes sent: {0}", u.EndSend(ar));
  messageSent = true;
static void SendMessage3(string server, string message)
  // create the udp socket
  UdpClient u = new UdpClient();

  Byte [] sendBytes = Encoding.ASCII.GetBytes(message);

  // send the message 
  // the destination is defined by the server name and port
  u.BeginSend(sendBytes, sendBytes.Length, server, listenPort,
              new AsyncCallback(SendCallback), u);

  // Do some work while we wait for the send to complete. For  
  // this example, we'll just sleep 
  while (!messageSent)

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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