SDK里面的例子，但是看不明白，请大家帮忙解析下。

Question

using System;
using System.Globalization;
using System.IO;
using System.Text;
using System.Threading;
using System.Net;
using System.Net.Sockets;
using System.Drawing;
using System.Windows.Forms;
class TalkForm:Form {    
    public TalkForm(Talker talker) {
        this.talker = talker;
        talker.Notifications += new 
                Talker.NotificationCallback(HandleTalkerNotifications);
        Splitter talkSplitter = new Splitter();
        Panel talkPanel = new Panel();        
        receiveText = new TextBox();
        sendText = new TextBox(); 
        receiveText.MaxLength = sendText.MaxLength = 65536;
        statusText = new Label();
        receiveText.Dock = DockStyle.Top;
        receiveText.Multiline = true;
        receiveText.ScrollBars = ScrollBars.Both;
        receiveText.Size = new Size(506, 192);
        receiveText.TabIndex = 1;
        receiveText.Text = "";
        receiveText.WordWrap = false;
        receiveText.ReadOnly = true;
        talkPanel.Anchor = (AnchorStyles.Top|AnchorStyles.Bottom
                    |AnchorStyles.Left|AnchorStyles.Right);
        talkPanel.Controls.AddRange(new Control[] {sendText,
                    talkSplitter,
                    receiveText});
        talkPanel.Size = new Size(506, 371);
        talkPanel.TabIndex = 0;
        talkSplitter.Dock = DockStyle.Top;
        talkSplitter.Location = new Point(0, 192);
        talkSplitter.Size = new Size(506, 6);
        talkSplitter.TabIndex = 2;
        talkSplitter.TabStop = false;
        statusText.Dock = DockStyle.Bottom;
        statusText.Location = new Point(0, 377);
        statusText.Size = new Size(507, 15);
        statusText.TabIndex = 1;
        statusText.Text = "Status:";
        sendText.Dock = DockStyle.Fill;
        sendText.Location = new Point(0, 198);
        sendText.Multiline = true;
        sendText.ScrollBars = ScrollBars.Both;
        sendText.Size = new Size(506, 173);
        sendText.TabIndex = 0;
        sendText.Text = "";
        sendText.WordWrap = false;
        sendText.TextChanged += new EventHandler(HandleTextChange);
        sendText.Enabled = false;
        AutoScaleBaseSize = new Size(5, 13);
        ClientSize = new Size(507, 392);
        Controls.AddRange(new Control[] {statusText,
                    talkPanel});
        Text = "WinTalk";
    }    
    protected override void OnClosed(EventArgs e){
        if(talker!=null){
            talker.Notifications -= new 
                Talker.NotificationCallback(HandleTalkerNotifications);
            talker.Dispose();
        }
        base.OnClosed(e);
    }
    private void HandleTalkerNotifications(
        Talker.Notification notify, Object data){
        switch(notify){
        case Talker.Notification.Initialized:
            break;
        case Talker.Notification.StatusChange:
            Talker.Status status = (Talker.Status)data;
            statusText.Text = String.Format("Status: {0}", status);
            if(status == Talker.Status.Connected){
                sendText.Enabled = true;
sendText.Focus();
            }
            break;
        case Talker.Notification.ReceivedAppend:
            receiveText.AppendText(data.ToString());       
            break;
        case Talker.Notification.ReceivedRefresh:
            receiveText.Text = data.ToString();
            receiveText.SelectionStart = Int32.MaxValue;
            receiveText.ScrollToCaret();        
            break;
        case Talker.Notification.Error:            
            Close(data.ToString());        
            break;
        case Talker.Notification.End:                                    
sendText.TextChanged -= new EventHandler(HandleTextChange); 
MessageBox.Show(this, data.ToString(), "Closing WinTalk");             
            Close();
            break;
        default:
            Close();
            break;
        }
    }
    private void HandleTextChange(Object sender, EventArgs e){
        if(talker != null){
            talker.SendTalk((sender as TextBox).Text);
        }        
    }
private void InitializeComponent()
{
this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(480, 273);
this.Name = "TalkForm";
}   
    private void Close(String message){   
        MessageBox.Show(message, "Error!");        
        Close();
    }
    private TextBox receiveText;        
    private TextBox sendText;    
    private Label statusText;
    private Talker talker;   
}
class App
{        
public static void Main(String[] args)
{        
if(ParseArgs(args))
{           
Talker talker = new Talker(endPoint, client);
TalkForm form = new TalkForm(talker);                   
talker.Start();
Application.Run(form);
}        
}
private static IPEndPoint endPoint;
private static bool client;
private static bool ParseArgs(String[] args)
{
try
{        
if(args.Length == 0)
{
client = false;
endPoint = new IPEndPoint(IPAddress.Any,5150);
return true;
}
if (args[0][0]!='/' && args[0][0]!='-') 
{
ShowUsage();
return false;
}
switch(Char.ToUpper(args[0][1], CultureInfo.InvariantCulture))
{
case 'L':
int port = 5150;
if(args.Length > 1)
{
port = Convert.ToInt32(args[1]);    
}
endPoint = new IPEndPoint(IPAddress.Any,port);
client = false;
break;
case 'C':
port = 5150;
String address = "127.0.0.1";
client = true;
if(args.Length > 1)
{
address = args[1];
port = Convert.ToInt32(args[2]);                                        
}                
endPoint = new IPEndPoint(Dns.Resolve(address).AddressList[0], port);
break;
default:
ShowUsage();
return false;
}
}
catch
{
ShowUsage();
return false;
}    
    
return true;
}
private static void ShowUsage()
{
MessageBox.Show("WinTalk [switch] [parameters...]\n\n"+
"  /L  [port]\t\t-- Listens on a port.  Default:  5150\n"+
"  /C  [address] [port]\t-- Connects to an address and port.\n\n"+
"Example Server - \n"+
"Wintalk /L\n\n"+
"Example Client - \n"+
"Wintalk /C ServerMachine 5150","WinTalk Usage");
}
}

Answer 1

class Talker:IDisposable{
    public Talker(IPEndPoint endPoint, bool client){
        this.endPoint = endPoint;
        this.client = client;
        socket = null;
        reader = null;
        writer = null;
        statusText = prevSendText = prevReceiveText = String.Empty;
    }
    ~Talker(){
        Dispose();
    }
    public void Dispose(){        
        GC.SuppressFinalize(this);
        if(reader != null){
            reader.Close();
            reader = null;
        }
        if(writer != null){
            writer.Close();
            writer = null;
        }
        if(socket != null){
            socket.Close();
            socket = null;
        }        
    }
    public delegate void NotificationCallback(Notification notify, Object data);
    public event NotificationCallback Notifications;
    public enum Notification{
        Initialized = 1,
        StatusChange,
        ReceivedRefresh,
ReceivedAppend,
        End,
        Error
    }
    public enum Status{
        Listening,
        Connected
    }
    public void Start(){
        ThreadPool.QueueUserWorkItem(new WaitCallback(EstablishSocket));
    }
    public void SendTalk(String newText){                
        String send;
        if((prevSendText.Length <= newText.Length) && String.CompareOrdinal(newText, 0, prevSendText, 0, prevSendText.Length)==0)
{
            String append = newText.Substring(prevSendText.Length);
            send = String.Format("A{0}:{1}", append.Length, append);
        }
else
{
            send = String.Format("R{0}:{1}", newText.Length, newText);
        }   
        writer.Write(send);
        writer.Flush();
        prevSendText = newText;
    }
    private void SetStatus(Status status)
{
        this.status = status;
        Notifications(Notification.StatusChange, status);
    }
    private void EstablishSocket(Object state){               
NetworkStream stream = null;
        try
{
            if(!client)
{
                Socket listener;
                
                try
{
                    listener = new Socket(AddressFamily.InterNetwork,SocketType.Stream, ProtocolType.Tcp);
                    listener.Blocking = true;
                    listener.Bind(endPoint);
                    SetStatus(Status.Listening);                    
                    listener.Listen(0);
                    socket = listener.Accept();
listener.Close();          
stream = new NetworkStream(socket);
reader = new StreamReader(stream);
writer = new StreamWriter(stream);
writer.Write("WINTALK .NET");
writer.Flush();
                }
catch(SocketException e)
{
                    if(e.ErrorCode == 10048)
{
                        client = true;
                        endPoint = new IPEndPoint(Dns.Resolve("127.0.0.1").AddressList[0], endPoint.Port);
                    }
else
{
                        Notifications(Notification.Error, "Error Initializing Socket:\n"+e.ToString());                        
                    }
                }                                    
            }
            if(client)
{
                Socket temp = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
                temp.Blocking = true;
                temp.Connect(endPoint);
                socket = temp;
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 5000);
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.SendTimeout, 5000);
stream = new NetworkStream(socket);
reader = new StreamReader(stream);
writer = new StreamWriter(stream);
char[] handshake = new char[12];
try
{
if (!(reader.Read(handshake,0,12)>0 && new string(handshake)=="WINTALK .NET"))
{
socket.Close();
socket = null;
}
else
{
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout , 0);
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.SendTimeout, 0);
}
}
catch
{
socket.Close();
socket = null;
}
            }
            if(socket != null)
{
                SetStatus(Status.Connected);                 
                Notifications(Notification.Initialized, this);                
ReceiveTalk();
Notifications(Notification.End, "Remote connection has closed.");
}
else
{
                Notifications(Notification.Error, 
                    "Failed to Establish Socket, did you specify the correct port?");
            }
        }
catch(IOException e)
{ 
            SocketException sockExcept = e.InnerException as SocketException; 
            if(sockExcept != null && 10054 == sockExcept.ErrorCode)
{
                Notifications(Notification.End, "Remote connection has closed.");
            }
else
{
if (Notifications != null)
Notifications(Notification.Error, "Socket Error:\n"+e.Message);
            }                
        }
catch(Exception e)
{              
            Notifications(Notification.Error, "Socket Error:\n"+e.Message);
        }
    }
    private void ReceiveTalk()
{
        char[] commandBuffer = new char[20];
        char[] oneBuffer = new char[1];
        int readMode = 1;
        int counter = 0;        
        StringBuilder text = new StringBuilder();
        while(readMode != 0)
{
            if(reader.Read(oneBuffer, 0, 1)==0)
{
                readMode = 0;
                continue;
            }
switch(readMode)
{
            case 1:        
                if(counter == commandBuffer.Length)
{
                    readMode = 0;
                    continue;
                }
                if(oneBuffer[0] != ':')
{
                    commandBuffer[counter++] = oneBuffer[0];
                }
else
{
                    counter = Convert.ToInt32(new String(commandBuffer, 1, counter-1));
                    if(counter>0)
{
                        readMode = 2;                            
                        text.Length = 0;
                    }
else if(commandBuffer[0] == 'R')
{
                        counter = 0;
                        prevReceiveText = String.Empty;
                        Notifications(Notification.ReceivedRefresh, prevReceiveText);
                    }
                }
                break;
            case 2:
                text.Append(oneBuffer[0]);
                if(--counter == 0)
{
                    switch(commandBuffer[0])
{
                    case 'R':
                        prevReceiveText = text.ToString();
Notifications(Notification.ReceivedRefresh, prevReceiveText);                    
                        break;
                    default:
string newText = text.ToString();
                        prevReceiveText += newText;
                        Notifications(Notification.ReceivedAppend, newText);                    
break;
                    }                    
                    readMode = 1;
                }
                break;
            default:
                readMode = 0;
                continue;
            }            
        }        
    }
    private Socket socket;
    private TextReader reader;
    private TextWriter writer;
    bool client;
    IPEndPoint endPoint;
    private String prevSendText;
    private String prevReceiveText;
    private String statusText;
    private Status status;    
}