@Override
  public void update(AnActionEvent e) {
    final DataContext dc = e.getDataContext();

    final Presentation presentation = e.getPresentation();

    // presentation.setVisible(isVisible(dc));
    presentation.setEnabled(isVisible(dc) && isEnabled(dc));
  }
  public void actionPerformed(AnActionEvent e) {
    final DataContext dc = e.getDataContext();
    if ((!isVisible(dc)) || (!isEnabled(dc))) return;

    final Project project = CommonDataKeys.PROJECT.getData(dc);
    final Iterable<Pair<VirtualFilePointer, FileStatus>> iterable =
        e.getRequiredData(VcsDataKeys.UPDATE_VIEW_FILES_ITERABLE);
    final Label before = (Label) e.getRequiredData(VcsDataKeys.LABEL_BEFORE);
    final Label after = (Label) e.getRequiredData(VcsDataKeys.LABEL_AFTER);
    final String selectedUrl = VcsDataKeys.UPDATE_VIEW_SELECTED_PATH.getData(dc);

    MyDiffRequestChain requestChain =
        new MyDiffRequestChain(project, iterable, before, after, selectedUrl);
    DiffManager.getInstance().showDiff(project, requestChain, DiffDialogHints.FRAME);
  }