C#监听器

Question

C#中什么叫做监听器，几个例子，最好给了简单的例子

Answer 1

监听端口吗？
看看这个：using System;
using System.Windows.Forms;
using System.Net.Sockets;
using System.IO;
namespace TCPSocketServer
{
    public class Server : Form
    {
        Button btnStartServer;
        private StreamWriter serverStreamWriter;
        private StreamReader serverStreamReader;        public Server()
        {
            //create StartServer button set its properties & event handlers 
            this.btnStartServer = new Button();
            this.btnStartServer.Text = "Start Server";
            this.btnStartServer.Click += new System.EventHandler(this.btnStartServer_Click);
            //add controls to form            this.Controls.Add(this.btnStartServer);
        }        ///Main Method
        public static void Main(string[] args)
        {
            //creat n display windows form            Server tcpSockServer = new Server();
            Application.Run(tcpSockServer);
        }        ///Start Server
        private bool StartServer()
        {
            //create server's tcp listener for incoming connection
            TcpListener tcpServerListener = new TcpListener(4444);
            tcpServerListener.Start(); //start server            Console.WriteLine("Server Started");
            this.btnStartServer.Enabled = false;
            //block tcplistener to accept incoming connection            Socket serverSocket = tcpServerListener.AcceptSocket();            try
            {
                if (serverSocket.Connected)
                {
                    Console.WriteLine("Client connected");
                    //open network stream on accepted socket                    NetworkStream serverSockStream = new NetworkStream(serverSocket);
                    serverStreamWriter = new StreamWriter
                    (serverSockStream);
                    serverStreamReader = new StreamReader(serverSockStream);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.StackTrace);
                return false;
            }            return true;
        }        ///Event handlers
        private void btnStartServer_Click(object sender, System.EventArgs e)
        {
            //start server
            if (!StartServer())
                Console.WriteLine("Unable to start server");            //sending n receiving msgs            while (true)
            {
                Console.WriteLine
                ("CLIENT: " + serverStreamReader.ReadLine());
                serverStreamWriter.WriteLine("Hi!");
                serverStreamWriter.Flush();
            }//while        }
    }
}

Answer 2

客户端代码：using System;
using System.Windows.Forms;
using System.Net.Sockets;
using System.IO;namespace TCPSocketClient
{
    public class Client : Form
    {
        private Button btnConnectToServer;
        private Button btnSendMessage;
        private StreamReader clientStreamReader;
        private StreamWriter clientStreamWriter;        public Client()
        {
            //create ConnectToServer button, set its properties & event handlers
            this.btnConnectToServer = new Button();
            this.btnConnectToServer.Text = "Connect";
            this.btnConnectToServer.Click +=
              new System.EventHandler(btnConnectToServer_Click);
            //create SendMessage button, set its properties & event handlers            this.btnSendMessage = new Button();
            this.btnSendMessage.Text = "Send Message";
            this.btnSendMessage.Top += 30;
            this.btnSendMessage.Width += 20;
            this.btnSendMessage.Click += new System.EventHandler(btnSendMessage_Click);
            //add controls to windows form            this.Controls.Add(this.btnConnectToServer);
            this.Controls.Add(this.btnSendMessage);
        }
        ///Main method
        public static void Main(string[] args)
        {
            //create n display windows form
            Client tcpSockClient = new Client();
            Application.Run(tcpSockClient);
        }        ///Connect to server
        private bool ConnectToServer()
        {
            //connect to server at given port
            try
            {
                TcpClient tcpClient = new TcpClient("localhost", 4444);
                Console.WriteLine("Connected to Server");
                //get a network stream from server                NetworkStream clientSockStream = tcpClient.GetStream();
                clientStreamReader = new StreamReader(clientSockStream);
                clientStreamWriter = new StreamWriter(clientSockStream);
            }
            catch (Exception e)
            {
                Console.WriteLine(e.StackTrace);
                return false;
            }
            return true;
        }        ///Event Handlers
        private void btnConnectToServer_Click(object sender, System.EventArgs e)
        {
            //connect to server
            if (!ConnectToServer())
                Console.WriteLine("Unable to connect to server");
        }
        private void btnSendMessage_Click(object sender, System.EventArgs e)
        {
            try
            {
                //send message to server
                clientStreamWriter.WriteLine("Hello!");
                clientStreamWriter.Flush();
                Console.WriteLine("SERVER: " + clientStreamReader.ReadLine());
            }
            catch (Exception se)
            {
                Console.WriteLine(se.StackTrace);
            }
        }
    }
}

Answer 3

为什么中间还有Main方法？
给解释下。。

Answer 4

Main方法是程序的入口，没有它程序从哪里开始执行？