Question

I am using Embarcadero RAD Studio XE2 Update 4 and the Indy package shipped with it.

My intention is to find a server in LAN with broadcast from a TIdUDPClient that waits for a response from the server to get its IP. Receiving the data works fine if I use the TIdUDPClient method ReceiveString with no arguments.

But when I try to use the overloaded version found in the Indy 10 Documentation version 10.5.8.3 coming with RAD Studio, it does not compile and shows ‘E2250: There is no overloaded version of ‘ReceiveString’ that can be called with these arguments’.
Here is my code:

unit Client;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, IdBaseComponent, IdComponent, IdUDPBase,
  IdUDPClient, Vcl.StdCtrls, IdGlobal;

type
  TFormLC = class(TForm)
    UDPClient: TIdUDPClient;
    LServer: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  FormLC: TFormLC;

implementation

{$R *.dfm}

function findServer:string;
var ans, ip : string;
    port: TIdPort;
begin
  with FormLC.UDPClient do begin
    Active := True;
    BroadcastEnabled:=True;
    Broadcast('ServerRequest', 1234);
    ans := ReceiveString(ip, port);
    Active := False;
  end;
  if SameText(ans, 'ServerAccept') then
    result := ip
  else
    result := '';
end;


procedure TFormLC.Button1Click(Sender: TObject);
var ans:string;
begin
  LServer.Caption := findServer;
end;

end.

I noticed that the online documentation of Indy differs from the documentation that comes with the IDE and tried it as described there, without succes.

Any help would be great!

Answer 1

Your issue is caused by the with statement, you are passing the port property of the TIdUDPClient instead of the local variable port to the ReceiveString method.

function findServer:string;
var ans, ip : string;
    port: TIdPort;
begin
  with FormLC.UDPClient do begin
    ....
    ans := ReceiveString(ip, port);//here you are passing the port property 
    Active := False;
  end;
  .... 
end;

As workaround rename you port local variable like so :

 function findServer:string;
var ans, ip : string;
    vport: TIdPort;
begin
  with FormLC.UDPClient do begin
    .... 
    ans := ReceiveString(ip, vport);//now will work
    Active := False;
  end;
end;

or even better don’t use the with statement.