unit untTResolve;

interface

uses Classes;

type
  TResolveEvent = procedure(Sender : TObject; Address : String; Ip : String) of Object;

type TResolve = class(TThread)
private
  _toResolve : String;
  FOnRes : TResolveEvent;

protected
  procedure execute; override;

public
  property OnIpResolved : TResolveEvent read FOnRes write FOnRes;
  procedure resolve(ip : String);
end;

implementation

{ TResolve }

procedure TResolve.execute;
var
  ResAddress : String;

begin
  inherited;

  // do resolving and all that stuff
  // ResAddress = fubar

  if assigend(FOnRes) then
    FOnRes(self, ResAddress, self._toResolve);

  self.Suspend();
end;

procedure TResolve.resolve(ip: String);
begin
  self._toResolve := ip;
  self.resume();
end;

end.

/// and the usage is....

procedure TForm1.Button1Click(Sender: TObject);
var
  res : TResolve;

begin
  res := TResolve.Create(true);
  res.OnIpResolved := self.HandleResolve;

  res.resolve();
end;

procedure TForm1.HandleResolve(Sender : TObject; Address : String; Ip : String);
begin
  listBox1.fubar := Address;
  // well normaly listBox1.items[...] and so on....
end;