关于信息传达的问题？(100分)

在三层的系统里，我要实现一个功能：客户端的某一个用户要向另一客户端的用户发出一个通知，并且即时接收得到，就类似QQ里的发信息一样，只要用户已经登记了系统，我发的信息，对方可以马上看到？

D6有例子

网中戏 ：我现在用的开发环境就是D6，能不能告诉我是哪个Demo？

你看看idudpserver这个控件。就可以知道怎么做。
还有，网上有整个indy的demo.

http://www.2ccc.com/article.asp?articleid=3437

还是实现不了，能不能提供详细一点的例子，意思是：一个客户端发一条信息给服务器，信息包括：发给某一客户端和内容，服务器在接收到信息后，再找到这个客户端，如果这个客户端已经登录了系统，就把信息发给他并自动接收。

我给你贴一段indy使用tcp协议实现的，和你的要求是一样．

{-----------------------------------------------------------------------------
Demo Name: ServerFrmMainUnit
Author: Helge Jung (helge@eco-logic-software.de)
Copyright: Indy Pit Crew
Purpose:
History: Improvements supplied by: Enver ALTIN
Date: 27/10/2002 00:23:25
Checked with Indy version: 9.0 - Allen O'Neill - Springboard Technologies Ltd - http://www.springboardtechnologies.com
-----------------------------------------------------------------------------
Notes:

Demonstration on how to use TIdTCPServer and TIdTCPClient
with using Threads and WriteBuffer/ReadBuffer

}

unit ServerFrmMainUnit;

interface

uses
Windows,Messages,SysUtils,Classes,Graphics,Controls,Forms,Dialogs,
StdCtrls,IdTCPServer,IdThreadMgr,IdThreadMgrDefault,IdBaseComponent,
IdComponent;

type
PClient=^TClient;
TClient=record // Object holding data of client (see events)
DNS:string[20]; { Hostname }
Connected, { Time of connect }
LastAction:TDateTime; { Time of last transaction }
Threadointer; { Pointer to thread }
end;

TServerFrmMain=class(TForm)
Server:TIdTCPServer;
CBServerActive:TCheckBox;
Protocol:TMemo;
IdThreadMgrDefault1:TIdThreadMgrDefault;

procedure CBServerActiveClick(Sender:TObject);
procedure ServerConnect(AThread:TIdPeerThread);
procedure ServerExecute(AThread:TIdPeerThread);
procedure ServerDisconnect(AThread:TIdPeerThread);
procedure FormCreate(Sender:TObject);
procedure FormClose(Sender:TObject; var Action:TCloseAction);

private

public
end;

var
ServerFrmMain:TServerFrmMain;
Clients:TThreadList; // Holds the data of all clients

implementation

uses GlobalUnit;

{$R *.DFM}

procedure TServerFrmMain.CBServerActiveClick(Sender:TObject);
begin
Server.Active:=CBServerActive.Checked;
end;

procedure TServerFrmMain.ServerConnect(AThread:TIdPeerThread);
var
NewClientClient;

begin
GetMem(NewClient,SizeOf(TClient));

NewClient.DNS:=AThread.Connection.LocalName;
NewClient.Connected:=Now;
NewClient.LastAction:=NewClient.Connected;
NewClient.Thread:=AThread;

AThread.Data:=TObject(NewClient);

try
Clients.LockList.Add(NewClient);
finally
Clients.UnlockList;
end;

Protocol.Lines.Add(TimeToStr(Time)+' Connection from "'+NewClient.DNS+'"');
end;

procedure TServerFrmMain.ServerExecute(AThread:TIdPeerThread);
var
ActClient,RecClientClient;
CommBlock,NewCommBlock:TCommBlock;
RecThread:TIdPeerThread;
i:Integer;

begin
if not AThread.Terminated and AThread.Connection.Connected then
begin
AThread.Connection.ReadBuffer(CommBlock,SizeOf(CommBlock));
ActClient:=PClient(AThread.Data);
ActClient.LastAction:=Now; // update the time of last action

if (CommBlock.Command='MESSAGE')or(CommBlock.Command='DIALOG') then
begin // 'MESSAGE': A message was send - forward or broadcast it
// 'DIALOG': A dialog-window shall popup on the recipient's screen
// it's the same code for both commands...

if CommBlock.ReceiverName='' then
begin // no recipient given - broadcast
Protocol.Lines.Add(TimeToStr(Time)+' Broadcasting '+CommBlock.Command+': "'+CommBlock.Msg+'"');
NewCommBlock:=CommBlock; // nothing to change ;-))

with Clients.LockList do
try
for i:=0 to Count-1 do // iterate through client-list
begin
RecClient:=Items; // get client-object
RecThread:=RecClient.Thread; // get client-thread out of it
RecThread.Connection.WriteBuffer(NewCommBlock,SizeOf(NewCommBlock),True); // send the stuff
end;
finally
Clients.UnlockList;
end;
end
else
begin // receiver given - search him and send it to him
NewCommBlock:=CommBlock; // again: nothing to change ;-))
Protocol.Lines.Add(TimeToStr(Time)+' Sending '+CommBlock.Command+' to "'+CommBlock.ReceiverName+'": "'+CommBlock.Msg+'"');
with Clients.LockList do
try
for i:=0 to Count-1 do
begin
RecClient:=Items;
if RecClient.DNS=CommBlock.ReceiverName then // we don't have a login function so we have to use the DNS (Hostname)
begin
RecThread:=RecClient.Thread;
RecThread.Connection.WriteBuffer(NewCommBlock,SizeOf(NewCommBlock),True);
end;
end;
finally
Clients.UnlockList;
end;
end;
end
else
begin // unknown command given
Protocol.Lines.Add(TimeToStr(Time)+' Unknown command from "'+CommBlock.MyUserName+'": '+CommBlock.Command);
NewCommBlock.Command:='DIALOG'; // the message should popup on the client's screen
NewCommBlock.MyUserName:='[Server]'; // the server's username
NewCommBlock.Msg:='I don''t understand your command: "'+CommBlock.Command+'"'; // the message to show
NewCommBlock.ReceiverName:='[return-to-sender]'; // unnecessary

AThread.Connection.WriteBuffer(NewCommBlock,SizeOf(NewCommBlock),True); // and there it goes...
end;
end;
end;

procedure TServerFrmMain.ServerDisconnect(AThread:TIdPeerThread);
var
ActClientClient;

begin
ActClient:=PClient(AThread.Data);
Protocol.Lines.Add(TimeToStr(Time)+' Disconnect from "'+ActClient^.DNS+'"');
try
Clients.LockList.Remove(ActClient);
finally
Clients.UnlockList;
end;
FreeMem(ActClient);
AThread.Data:=nil;
end;

procedure TServerFrmMain.FormCreate(Sender:TObject);
begin
Clients:=TThreadList.Create;
end;

procedure TServerFrmMain.FormClose(Sender:TObject; var Action:TCloseAction);
begin
Server.Active:=False;
Clients.Free;
end;

end.

／／相关的结构定义，
unit GlobalUnit;

interface

type
TCommBlock = record // the Communication Block used in both parts (Server+Client)
Command,
MyUserName, // the sender of the message
Msg, // the message itself
ReceiverName: string[100]; // name of receiver
end;

implementation

end.

请恕小弟愚钝，能不能把例子发到我的邮箱：sdiwen88@yahoo.com.cn,谢谢了