UdpClient.BeginReceive(AsyncCallback, Object) UdpClient.BeginReceive(AsyncCallback, Object) UdpClient.BeginReceive(AsyncCallback, Object) UdpClient.BeginReceive(AsyncCallback, Object) Method

Definition

Receives a datagram from a remote host asynchronously.

public:
 IAsyncResult ^ BeginReceive(AsyncCallback ^ requestCallback, System::Object ^ state);
public IAsyncResult BeginReceive (AsyncCallback requestCallback, object state);
member this.BeginReceive : AsyncCallback * obj -> IAsyncResult
Public Function BeginReceive (requestCallback As AsyncCallback, state As Object) As IAsyncResult

Parameters

requestCallback
AsyncCallback AsyncCallback AsyncCallback AsyncCallback

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

state
Object Object Object 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.

Returns

An IAsyncResult object that references the asynchronous receive.

Examples

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

private:
    static int listenPort = 13000;

public:
    value struct UdpState
    {
    public:
        UdpClient^ udpClient;
        IPEndPoint^ ipEndPoint;
    };

    static bool isMessageReceived;

    static void ReceiveCallback(IAsyncResult^ asyncResult)
    {
        UdpClient^ udpClient =
            ((UdpState)(asyncResult->AsyncState)).udpClient;
        IPEndPoint^ ipEndPoint =
            ((UdpState)(asyncResult->AsyncState)).ipEndPoint;

        array<Byte>^ receiveBytes =
            udpClient->EndReceive(asyncResult, ipEndPoint);
        String^ receiveString =
            Encoding::ASCII->GetString(receiveBytes);

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

    static void ReceiveMessages()
    {
        // Receive a message and write it to the console.
        IPEndPoint^ ipEndPoint = gcnew IPEndPoint(IPAddress::Any, listenPort);
        UdpClient^ udpClient = gcnew UdpClient(ipEndPoint);

        UdpState^ udpState = gcnew UdpState();
        udpState->ipEndPoint = ipEndPoint;
        udpState->udpClient = udpClient;

        Console::WriteLine("listening for messages");
        udpClient->BeginReceive(gcnew AsyncCallback(ReceiveCallback),
            udpState);

        // Do some work while we wait for a message. For this example,
        // we'll just sleep
        while (!isMessageReceived)
        {
            Thread::Sleep(100);
        }
    }
public struct UdpState
{
    public UdpClient u;
    public IPEndPoint e;
}

public static bool messageReceived = false;

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

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

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

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

Remarks

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.

Applies to