【发布时间】：2020-10-02 16:43:01
【问题描述】：
我需要通过 TCP 异步发送数据。它是一个字符串集合ICollection<string>。
我搜索并找到了一个很好的starting example from Microsoft（见下文）。该示例似乎在.NET Framework 下，但我认为它也适用于.NET Core。
我在做什么：
-
我将代码重新用作非静态类
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我想发送一组字符串
ICollection<string>。我知道我可以重写它以在 main 方法中发送字符串集合。没问题。 -
我希望收到对发送的每条消息的响应并对其进行处理。当前响应静态存储在
private static String response = String.Empty;中。我不希望它是静态的。我想要一个局部方法变量。 -
我的挑战从项目 3. 开始。如何返回似乎只能从
private static void ReceiveCallback( IAsyncResult ar )内部访问的响应消息我不认为将其更改为
private static string ReceiveCallback( IAsyncResult ar )会起作用。如果是这样，我如何从client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReceiveCallback), state);读取它？
我在一篇非常古老的帖子上针对我发现的一个类似问题提出了 300 分赏金：C# Asyn. Socket Programming。很高兴奖励任何在这里和那里回答的人。
另外一个问题是：建议的做法是打开一个 TCP 连接，发送多条消息，然后关闭它？还是为正在发送的每条消息打开一个 TCP 连接？
微软示例
using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Text;
// State object for receiving data from remote device.
public class StateObject {
// Client socket.
public Socket workSocket = null;
// Size of receive buffer.
public const int BufferSize = 256;
// Receive buffer.
public byte[] buffer = new byte[BufferSize];
// Received data string.
public StringBuilder sb = new StringBuilder();
}
public class AsynchronousClient {
// The port number for the remote device.
private const int port = 11000;
// ManualResetEvent instances signal completion.
private static ManualResetEvent connectDone =
new ManualResetEvent(false);
private static ManualResetEvent sendDone =
new ManualResetEvent(false);
private static ManualResetEvent receiveDone =
new ManualResetEvent(false);
// The response from the remote device. <------ ### the response data that I want to access, non statically
private static String response = String.Empty;
private static void StartClient() {
// Connect to a remote device.
try {
// Establish the remote endpoint for the socket.
// The name of the
// remote device is "host.contoso.com".
IPHostEntry ipHostInfo = Dns.GetHostEntry("host.contoso.com");
IPAddress ipAddress = ipHostInfo.AddressList[0];
IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);
// Create a TCP/IP socket.
Socket client = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
// Connect to the remote endpoint.
client.BeginConnect( remoteEP,
new AsyncCallback(ConnectCallback), client);
connectDone.WaitOne();
// Send test data to the remote device.
Send(client,"This is a test<EOF>");
sendDone.WaitOne();
// Receive the response from the remote device.
Receive(client);
receiveDone.WaitOne();
// Write the response to the console.
Console.WriteLine("Response received : {0}", response);
// Release the socket.
client.Shutdown(SocketShutdown.Both);
client.Close();
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
private static void ConnectCallback(IAsyncResult ar) {
try {
// Retrieve the socket from the state object.
Socket client = (Socket) ar.AsyncState;
// Complete the connection.
client.EndConnect(ar);
Console.WriteLine("Socket connected to {0}",
client.RemoteEndPoint.ToString());
// Signal that the connection has been made.
connectDone.Set();
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
private static void Receive(Socket client) {
try {
// Create the state object.
StateObject state = new StateObject();
state.workSocket = client;
// Begin receiving the data from the remote device.
client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReceiveCallback), state); //<------ The receive callback is here, how do I return the result to the caller?
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
private static void ReceiveCallback( IAsyncResult ar ) {
try {
// Retrieve the state object and the client socket
// from the asynchronous state object.
StateObject state = (StateObject) ar.AsyncState;
Socket client = state.workSocket;
// Read data from the remote device.
int bytesRead = client.EndReceive(ar);
if (bytesRead > 0) {
// There might be more data, so store the data received so far.
state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead));
// Get the rest of the data.
client.BeginReceive(state.buffer,0,StateObject.BufferSize,0,
new AsyncCallback(ReceiveCallback), state);
} else {
// All the data has arrived; put it in response.
if (state.sb.Length > 1) {
response = state.sb.ToString(); //<--------- ### Where it is assigned, I want it returned
}
// Signal that all bytes have been received.
receiveDone.Set();
}
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
private static void Send(Socket client, String data) {
// Convert the string data to byte data using ASCII encoding.
byte[] byteData = Encoding.ASCII.GetBytes(data);
// Begin sending the data to the remote device.
client.BeginSend(byteData, 0, byteData.Length, 0,
new AsyncCallback(SendCallback), client);
}
private static void SendCallback(IAsyncResult ar) {
try {
// Retrieve the socket from the state object.
Socket client = (Socket) ar.AsyncState;
// Complete sending the data to the remote device.
int bytesSent = client.EndSend(ar);
Console.WriteLine("Sent {0} bytes to server.", bytesSent);
// Signal that all bytes have been sent.
sendDone.Set();
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
public static int Main(String[] args) {
StartClient();
return 0;
}
}
【问题讨论】：
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为您的通信类创建一个事件（类似于 IncomingData）并在 ReceiveCallback 中触发它。确保委托具有合适的参数来包含响应。如果这样做，客户端类可以订阅 IncomingData 事件并收到收到的每个响应的通知。
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根据 TCP 连接：为每条消息打开一个新的 TCP 连接并不高效，因为如果您需要持续的消息交换，这将需要为每个新连接重新握手。不过，这取决于您需要连接到这些设备的频率以及在每个会话中您要与它们交换多少消息。由于 TCP 是一种面向连接的协议，因此即使没有实际的数据流，连接也可以无限期地保持打开状态。
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谢谢@FandangoOnCore，但代码会是什么样子？
标签： c# asynchronous .net-core tcp tcpclient