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);
  }
 private boolean isVisible(final DataContext dc) {
   final Project project = CommonDataKeys.PROJECT.getData(dc);
   return (project != null)
       && (VcsDataKeys.LABEL_BEFORE.getData(dc) != null)
       && (VcsDataKeys.LABEL_AFTER.getData(dc) != null);
 }