MainForm:

var
  IndyThread: TDownloadThread;

....

  IndyThread := TDownloadThread.Create(True);
  IndyThread.FreeOnTerminate := True;
  IndyThread.URL := LinkList.Items.Item[i].Caption;
  IndyThread.FilePath := DownloadPfad;
  IndyThread.RsUsername := frmOptions.edtRSUsername.Text;
  IndyThread.RsPassword := frmOptions.edtRSPassword.Text;
  IndyThread.Resume;

  IndyThread := TDownloadThread.Create(True);
  IndyThread.FreeOnTerminate := True;
  IndyThread.URL := LinkList.Items.Item[i].Caption;
  IndyThread.FilePath := DownloadPfad;
  IndyThread.RsUsername := frmOptions.edtRSUsername.Text;
  IndyThread.RsPassword := frmOptions.edtRSPassword.Text;
  IndyThread.Resume;

....

unit ThreadUnit;

interface

uses
  Classes, SysUtils, Windows, IdBaseComponent, IdComponent, IdTCPConnection, IdTCPClient, IdHTTP, IdException, ComCtrls;

var
  is_abort: Boolean;

type
  TWorkBeginEvent = procedure(ASender: TObject; AWorkMode: TWorkMode; AWorkCountMax: Integer) of object;
  TWorkEvent = procedure(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Integer) of object;
  TWorkEndEvent = procedure(ASender: TObject; AWorkMode: TWorkMode) of object;
  TDownloadThread = class(TThread)
  private
    { Private-Deklarationen }
    FURL: string;
    FID: string;
    FFMessage: string;
    FFilePath: string;
    FFileName: string;
    FWorkCountMax: Integer;
    FWorkCount: Integer;

    IdHTTPDownload: TIdHTTP;
    filestream: TFileStream;

    procedure ShowStatus;
    procedure ShowEnd;
    procedure Error;
    procedure Successful;
    procedure Abort;
    procedure FWorkBeginEvent(ASender: TObject; AWorkMode: TWorkMode; AWorkCountMax: Integer);
    procedure FWorkEvent(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Integer);
    procedure FWorkEndevent(ASender: TObject; AWorkMode: TWorkMode);
  public
    property URL: string read FURL write FURL;
    property FilePath: string read FFilePath write FFilePath;
  protected
    procedure Execute; override;
  end;

implementation

uses
  MainU, GlobalsU;


{ TDownloadThread }


procedure TDownloadThread.Execute;
begin
  IdHTTPDownload := TIdHTTP.Create(nil);
  is_abort := False;

  try

    IdHTTPDownload.OnWorkBegin := FWorkBeginEvent;
    IdHTTPDownload.OnWork := FWorkEvent;
    IdHTTPDownload.OnWorkEnd := FWorkEndevent;


    FFileName := SetFileName(FURL);
    FID := FFileName;

    filestream := TFileStream.Create(FFilePath + FFileName, fmCreate);

    try
      IdHTTPDownload.Get(FURL, filestream);
    except
      on E: Exception do
      begin
        FFMessage := E.message;
        Synchronize(Error);
      end;
    end;

  finally
    IdHTTPDownload.Free;
    filestream.Free;
  end;
end;


procedure TDownloadThread.FWorkBeginEvent(ASender: TObject; AWorkMode: TWorkMode; AWorkCountMax: Integer);
begin
  FWorkCountMax := AWorkCountMax;

  Synchronize(ShowStatus);
end;


procedure TDownloadThread.FWorkEvent(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Integer);
begin
  FWorkCount := AWorkCount;
 
  if is_abort then
    Synchronize(Abort); // Wenn is_abort dann Download abbrechen

  // Berechnen der Statuswerte


  Synchronize(ShowStatus);
end;


procedure TDownloadThread.FWorkEndevent(ASender: TObject; AWorkMode: TWorkMode);
begin
  if not is_abort then
  begin
    Synchronize(ShowEnd);
    Synchronize(Successful);
  end;
end;


procedure TDownloadThread.ShowStatus;
begin
  // Zugriff auf die Vcl der Mainform
end;


procedure TDownloadThread.Successful;
begin
  // Zugriff auf die Vcl der Mainform
end;

procedure TDownloadThread.ShowEnd;
begin
  // Zugriff auf die Vcl der Mainform
end;

procedure TDownloadThread.Error;
begin
  // Zugriff auf die Vcl der Mainform
end;

procedure TDownloadThread.Abort;
begin
  // Download abbrechen
  IdHTTPDownload.Disconnect;
  // Zugriff auf die Vcl der Mainform
end;


end.