@Override
  protected void onSaveInstanceState(@NonNull Bundle outState) {
    // If there's an animation in progress, cancel it first to ensure our state is up-to-date.
    if (mCurrentAnimator != null) {
      mCurrentAnimator.cancel();
    }

    super.onSaveInstanceState(outState);
    outState.putInt(KEY_CURRENT_STATE, mCurrentState.ordinal());
    outState.putString(
        KEY_CURRENT_EXPRESSION,
        mTokenizer.getNormalizedExpression(mFormulaEditText.getCleanText()));
  }
 protected String getNormalizedExpression(String expr) {
   return mTokenizer.getNormalizedExpression(expr);
 }