UdpClient.BeginReceive(AsyncCallback, Object) 方法

定义

命名空间:

System.Net.Sockets

程序集:

System.Net.Sockets.dll

Source:

UDPClient.cs

从远程主机异步接收数据报。

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

参数

requestCallback

AsyncCallback

一个 AsyncCallback 委托，它引用操作完成时要调用的方法。

state

Object

一个用户定义的对象，其中包含接收操作的相关信息。 当操作完成时，此对象会被传递给 requestCallback 委托。

返回

IAsyncResult

一个 IAsyncResult 对象，它引用异步接收。

示例

下面的代码示例使用 BeginReceive 异步接收服务器响应。

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);
    }
}

注解

BeginReceive异步操作必须通过调用 EndReceive 方法来完成。 通常，委托会调用 requestCallback 方法。

在操作完成之前，此方法不会阻止。 若要在操作完成之前阻止，请使用 Receive 方法。

有关使用异步编程模型的详细信息，请参阅 异步调用同步方法。