private void gridChange(Object itemId) {
    Collection<Object> ids = (Collection<Object>) gridFilter.getGrid().getValue();

    Button btnCheck = (Button) commandbar.getButton(COMMAND.CHECK.getValue());
    Button btnFavorite = (Button) commandbar.getButton(COMMAND.POP_MY_FAVORITE.getValue());
    Button btnCompare = (Button) commandbar.getButton(COMMAND.COMPARE.getValue());

    if (ids.size() != 0) {
      btnCompare.setEnabled(true);

      List<Item> selection = gridFilter.getGrid().getSelection();
      // 選擇多筆時, 只有btnCompare有可能Enabeld
      if (selection.size() > 1) {
        menu.setMenuBarEnabled(false);
        btnCheck.setEnabled(false);
        btnFavorite.setEnabled(false);
      } else {
        menu.setMenuBarEnabled(true);
        btnCheck.setEnabled(true);
        btnFavorite.setEnabled(true);
      }
      // 沒選到任何資料時
    } else {
      menu.setMenuBarEnabled(false);
      btnCheck.setEnabled(false);
      btnFavorite.setEnabled(false);
      btnCompare.setEnabled(false);
    }
  }
 private void perform(String instruction) {
   if (instruction.equals(COMMAND.CHECK.getValue())) {
     check(instruction);
   } else if (instruction.equals(COMMAND.POP_MY_FAVORITE.getValue())) {
     popMyFavorite(instruction);
   } else if (instruction.equals(COMMAND.SAVE_MY_FAVORITE.getValue())) {
     saveMyFavorite();
   } else if (instruction.equals(COMMAND.CLOSE_MY_FAVORITE.getValue())) {
     closeMyFavorite();
   } else if (instruction.equals(COMMAND.COMPARE.getValue())) {
     compare();
   } else if (instruction.equals(COMMAND.RESET.getValue())) {
     refresh();
   }
 }