Exam class - box around correct choice letter

Question

I'm typing an exam in the exam class and I would like to put a box, like the one produced by \fbox, around the correct letter in the choices environment (when \printanswers is used).

For example,

What is 2+2?
\begin{choices}
\choice 1
\choice 2
\choice 3
\correctchoice 4
\end{choices}

puts a box around the letter D, but not around the full question as this answer does.

Does anyone have a solution for this?

Answer 1

EDIT: Work with exam-randomizechoices package.

documentclass[10pt,a4paper,answers]{exam}
\usepackage[T1]{fontenc}

\usepackage[randomize,overload]{exam-randomizechoices}

\newcommand{\correctchoicelabel}{\fbox{\thechoice}}
\CorrectChoiceEmphasis{\renewcommand{\choicelabel}{\correctchoicelabel}}

\begin{document}
    \begin{questions}
        \question What is 2+2?
        \begin{choices}
            \choice 1
            \choice 2
            \choice 3
            \CorrectChoice 4
        \end{choices}
    \end{questions}
\end{document}