C＃ TCP客户端窗体应用程序异步接收方式

1. 程序界面设计

大概设计一个如下的简单界面。

2. 各部分核心代码

2.1连接服务端

当请求连接按钮按下时，会触发点击事件，然后进行连接服务端请求。

private void btnConnect_Click(object sender, EventArgs e)
{
    
    try
    {
    
        if (IsConnected == false)
        {
    
            tcpClient = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);    // 创建一个Socket套接字 
            IPAddress ipaddress = IPAddress.Parse(cbbHostIP.Text);
            EndPoint point = new IPEndPoint(ipaddress, int.Parse(tbHostPort.Text));

            tcpClient.Connect(point);

            tcpClient.BeginReceive(recieveBuffer, 0, recieveBuffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
            IsConnected = true;
            btnConnect.Text = "断开连接";
        }
        else
        {
    
            tcpClient.Disconnect(false);
            IsConnected = false;
            btnConnect.Text = "请求连接";
        }
    }
    catch (Exception ex)
    {
    
        MessageBox.Show(ex.ToString());
    }
}

按下连接时，先创建一个socket套接字，然后从控件中获得用户输入的服务端IP和端口，然后进行连接。

最重要的是，这里进行了异步接收设计，设置了接收回调函数 ReceiveCallback。

2.2 发送数据

因为发送数据，是用户主动按下“发送”按钮发送的，所以比较简单，只要有按下发送按钮的点击事件，就发送数据。

private void btnSend_Click(object sender, EventArgs e)
{
    
    if (IsConnected == true)
    {
    
        tcpClient.Send(tbSend.Text.GetBytes("GBK"));
    }
    else
    {
    
        MessageBox.Show("请先连接服务端");
    }
}

2.3 接收数据

接收数据采用异步接收方式，因为无法确定服务端什么时候会发送数据给客户端。

private void ReceiveCallback(IAsyncResult AR)
{
    
    // Check how much bytes are recieved and call EndRecieve to finalize handshake
    try
    {
    
        int recieved = tcpClient.EndReceive(AR);

        if (recieved <= 0)
            return;

        string message = Encoding.GetEncoding("GBK").GetString(recieveBuffer, 0, recieved);     // 只将接收到的数据进行转化

        Print(message);

        // Start receiving again
        tcpClient.BeginReceive(recieveBuffer, 0, recieveBuffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
    }
    catch (SocketException ex)
    {
    
        MessageBox.Show(ex.ToString());
    }
}

其中，ReceiveCallback 函数是接收的回调函数。如果有数据接收，那么真正接收数据的处理过程，是在这个回调函数完成的。

3. 整个工程源码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Windows.Forms;

namespace Net_assistance
{
    
    public partial class Form1 : Form
    {
    
        public static Socket tcpClient;
        bool IsConnected = false;
        private byte[] recieveBuffer = new byte[8142];

        public Form1()
        {
    
            InitializeComponent();
            Control.CheckForIllegalCrossThreadCalls = false;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
    
            // 获取本地可用的IP地址
            string strHostIP = Dns.GetHostName();
            IPAddress[] ipadrlist = Dns.GetHostAddresses(strHostIP);
            foreach (IPAddress ipaddr in ipadrlist)
            {
    
                if (ipaddr.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
                    cbbHostIP.Items.Add(ipaddr.ToString());
            }
            cbbHostIP.Items.Add("127.0.0.1");   // 最后加上回环测试地址
            cbbHostIP.SelectedIndex = 0;

            tbHostPort.Text = "8080";

            tbSend.Text = "hello world!";
        }

        private void Print(string msg)
        {
    
            tbRecv.AppendText($"[{
      DateTime.Now.ToString("yyy-MM-dd HH.mm.ss.fff")}] {
      msg}\r\n");
        }


        private void ReceiveCallback(IAsyncResult AR)
        {
    
            // Check how much bytes are recieved and call EndRecieve to finalize handshake
            try
            {
    
                int recieved = tcpClient.EndReceive(AR);

                if (recieved <= 0)
                    return;

                string message = Encoding.GetEncoding("GBK").GetString(recieveBuffer, 0, recieved);     // 只将接收到的数据进行转化

                Print(message);

                // Start receiving again
                tcpClient.BeginReceive(recieveBuffer, 0, recieveBuffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
            }
            catch (SocketException ex)
            {
    
                MessageBox.Show(ex.ToString());
            }
        }

        private void btnConnect_Click(object sender, EventArgs e)
        {
    
            try
            {
    
                if (IsConnected == false)
                {
    
                    tcpClient = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);    // 创建一个Socket套接字 
                    IPAddress ipaddress = IPAddress.Parse(cbbHostIP.Text);
                    EndPoint point = new IPEndPoint(ipaddress, int.Parse(tbHostPort.Text));

                    tcpClient.Connect(point);

                    tcpClient.BeginReceive(recieveBuffer, 0, recieveBuffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
                    IsConnected = true;
                    btnConnect.Text = "断开连接";
                }
                else
                {
    
                    tcpClient.Disconnect(false);
                    IsConnected = false;
                    btnConnect.Text = "请求连接";
                }
            }
            catch (Exception ex)
            {
    
                MessageBox.Show(ex.ToString());
            }
        }

        private void btnSend_Click(object sender, EventArgs e)
        {
    
            if (IsConnected == true)
            {
    
                tcpClient.Send(tbSend.Text.GetBytes("GBK"));
            }
            else
            {
    
                MessageBox.Show("请先连接服务端");
            }
        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
    
            if (IsConnected == true)
            {
    // 关闭窗口时，如果正在连接着服务端，那么断开连接后再退出
                tcpClient.Disconnect(false);
            }
        }
    }
}

4. 测试

先用网络调试助手打开一个服务端。如下：

然后打开我们自己写的客户端程序，输入服务端的IP和端口后，点击连接。这时可以看到服务端监测到有有客户端的接入了，这时就可以互相收发数据了，效果如下：