Can I underline text in an Android layout?

It can be achieved if you are using a string resource xml file, which supports HTML tags like <b></b>, <i></i> and <u></u>.

<resources>
    <string name="your_string_here">This is an <u>underline</u>.</string>
</resources>

If you want to underline something from code use:

TextView textView = (TextView) view.findViewById(R.id.textview);
SpannableString content = new SpannableString("Content");
content.setSpan(new UnderlineSpan(), 0, content.length(), 0);
textView.setText(content);