UnderlineBindingAdapter.java

    /**
     * Underline a portion of the text.
     *
     * @param view     The TextView containing the text to underline.
     * @param spanSize an array that contain the start index and the end index.
     */
    @android.databinding.BindingAdapter("underline")
    public static void underlineText(TextView view, @NonNull int[] spanSize) {
        if (view != null && spanSize.length == 2) {
            SpannableString content = new SpannableString(view.getText());
            content.setSpan(new UnderlineSpan(), spanSize[0], spanSize[1], 0);
            view.setText(content);
        }
    }