Client's udpserver don't response - delphi

Question

My server form has stringgride that accept only 4 tcp connected user
For this purpose, I put udpclient in my server and udpserver in clients
In tcp-onconnect event in server form :
//Server Side has udp client
procedure TForm1.IdTCPServer1Connect(AThread: TIdPeerThread);
begin
//when fifth user want to connect to tcpserver
//server first ensure at list one of the 4 connected user in grid has disconnected
//by send udp broadcast to 4 user
//but in this timeout None of these users do not respond , Although still connected
IdUDPClient1.Broadcast('IP', 1718);
For i:=1 To 4 Do
begin
IPList.Add(IdUDPClient1.ReceiveString(200););
end;
end;
//Client Side has udp server
procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
ABinding: TIdSocketHandle);
begin
//
ip:=GetipAddress();
ABinding.SendTo(ABinding.PeerIP, ABinding.PeerPort, ip[1], Length(ip));
end;
I run ethereal in client to check network and saw udp massage send from server to client but client do not respond.
Please help me what's my code problems

Answer 1

Your TIdUDPServer.OnUDPRead event handler does not have the correct signature, not even close. TIdUDPServer does not use TIdPeerThread at all, only TIdTCPServer does. You need to do something more like this instead:
Server:
procedure TForm1.IdTCPServer1Connect(AThread: TIdPeerThread);
begin
//when fifth user want to connect to tcpserver
//server first ensure at list one of the 4 connected user in grid has disconnected
//by send udp broadcast to 4 user
//but in this timeout None of these users do not respond , Although still connected
IPList.Clear;
IdUDPServer1.Broadcast('IP', 1718);
Sleep(1000);
end;
procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream; ABinding: TIdSocketHandle);
var
S: String;
begin
if AData.Size > 0 then
begin
SetLength(S, AData.Size);
AData.ReadBuffer(S[1], AData.Size);
IPList.Add(S);
end;
end;
Client:
procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream; ABinding: TIdSocketHandle);
var
S: String;
begin
if AData.Size > 0 then
begin
SetLength(S, AData.Size);
AData.ReadBuffer(S[1], AData.Size);
end;
if S = 'IP' then
begin
S := ABinding.IP;
if (S = '') or (S = '0.0.0.0') then
S := GStack.LocalAddress;
ABinding.SendTo(ABinding.PeerIP, ABinding.PeerPort, S[1], Length(S));
end;
end;