function CopyFileProgress(TotalFileSize, TotalBytesTransferred, StreamSize,
  StreamBytesTransferred: LARGE_INTEGER; dwStreamNumber, dwCallbackReason,
  hSourceFile, hDestinationFile, lpData: DWORD): DWORD; stdcall;
begin
  Application.ProcessMessages;
  if CancelCopy = True then
  begin
    ShowMessage('Abbruch');
    result := PROGRESS_CANCEL;
    Form1.ProgressBar1.Position := 0;
    Exit;
  end
  else
  Application.ProcessMessages;
  case dwCallbackReason of
    CALLBACK_CHUNK_FINISHED:
      begin
        Form1.ProgressBar1.Position := TotalBytesTransferred.QuadPart;
        result := PROGRESS_CONTINUE;
      end;
    CALLBACK_STREAM_SWITCH:
      begin
        Form1.ProgressBar1.Max := TotalFileSize.QuadPart;
        result := PROGRESS_CONTINUE;
      end;
    end;
end;


procedure TForm1.Button1Click(Sender: TObject);
var
  Cancel: PBOOL;
begin
  CancelCopy := False;
  Cancel := nil;
  CopyFileEx('C:\aaa.exe', 'D:\aaa.exe',
    @CopyFileProgress, nil, Cancel, 0);
  Form1.ProgressBar1.Position := 0;
end;


procedure TForm1.Button2Click(Sender: TObject);
begin
  CancelCopy := True;
end;

end.