type
  TForm2 = class(TForm)
    OtherThread: TWCThread;
    VeryHardTask: TTask;
    butStart: TButton;
    progressBar: TProgressBar;
    procedure butStartClick(Sender: TObject);
    procedure VeryHardTaskExecute(const Sender: TTask; const Msg: Word; var Param: Variant);
    procedure VeryHardTaskProgress(const Sender: TTask; const Msg, Value: Word);
    procedure VeryHardTaskFinish(const Sender: TTask; const Msg: Word; const Param: Variant);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.butStartClick(Sender: TObject);
begin
    progressBar.Position := 0;
    VeryHardTask.Start;
end;

procedure TForm2.VeryHardTaskExecute(const Sender: TTask; const Msg: Word; var Param: Variant);
var i: integer;
begin
    // other thread
    i := 0;
    while (i < 100) and (not Sender.Terminated) do begin
        Sender.WaitMs(100);
        inc(i);
        Sender.PostProgress(i);
    end;
end;

procedure TForm2.VeryHardTaskFinish(const Sender: TTask; const Msg: Word; const Param: Variant);
begin
    // very hard task finished
    ShowMessage('Finished');
end;

procedure TForm2.VeryHardTaskProgress(const Sender: TTask; const Msg, Value: Word);
begin
    // from sender.postProgress
    progressBar.Position := Value;
end;