Printing answer on dotted line exam class

Question

I am making a worksheet for a task for my teachertraining. My worksheet should leave the students enough place to answer, but also show what answer I expect.

The exam-class is perfect for making worksheets, however, I have one problem: I am using dotted lines for answers. If I print the answer, the dotted lines disappear and instead, my answer is printed in a box (which wraps perfectly around the answer, thus not showing how much place I would leave for the students to answer).

Is there some way, to make the answer appear on the dotted lines? This way, I can show my expected answer and how much place I think students would need. I am aware of the answerline-command, but I prefer dotted lines.

EDIT: As per comment, some code to show my problem:

1) version with answering lines, without answer:

\documentclass[11pt]{exam}

\setlength\dottedlinefillheight{.25in}

\begin{document}
\begin{questions}
   \question What is $2 + 2$?
   \begin{solutionordottedlines}[0.5in]
   This sum equals $4$.
\end{solutionordottedlines}
\end{document}

2) version with answer, but the dotted lines disappeared

\documentclass[11pt, answers]{exam}

\setlength\dottedlinefillheight{.25in}

\begin{document}
   \begin{questions}
   \question What is $2 + 2$?
   \begin{solutionordottedlines}[0.5in]
   This sum equals $4$.
   \end{solutionordottedlines}
\end{document}

Question: how to combine both documents, such that, when the answer is displayed, it appears on top of the dotted lines, while keeping the original amount of dotted lines?

Answer 1

Based on this answer, with some changes (using ulem package), following solution maybe used.

    \documentclass[11pt, answers]{exam}
    \usepackage[normalem]{ulem} 
    \newbox\allanswers
    \setbox\allanswers=\vbox{}
    \newenvironment{answer}
    {%
      \global\setbox\allanswers=\vbox\bgroup
      \unvbox\allanswers
    }%
    {%
      \bigbreak
      \egroup
      }
    \newcommand{\showanswers}{\unvbox\allanswers}
    \begin{document}
       \begin{questions}
       \question What is $2 + 2$?
       \begin{answer}
      \dotuline{ This sum equals $4$. Hence the answer is "four". Also the answer is $2^2$}
       \end{answer}
       \vspace{0.5cm}
       \showanswers
       \end{questions}
    \end{document}

EDIT: The answer is displayed, it appears on top of the dotted lines, while keeping the original amount of dotted lines.

\documentclass[11pt]{exam}
\newbox\allanswers
\setbox\allanswers=\vbox{}
\newenvironment{answer}
{%
  \global\setbox\allanswers=\vbox\bgroup
  \unvbox\allanswers
}%
{%
  \bigbreak
  \egroup
  }
\newcommand{\showanswers}{\unvbox\allanswers}
\setlength\dottedlinefillheight{.25in}
\begin{document}
   \begin{questions}
   \question What is $2 + 2$?
   \begin{answer}
   This sum equals $4$. This sum equals $4$. This sum equals $4$. This sum equals $4$. This sum equals $4$.This sum equals $4$. This sum equals $4$. This sum equals $4$. This sum equals $4$.
   \begin{solutionordottedlines}[0.5in]
   \end{solutionordottedlines}
   \end{answer}

   \vspace{0.5cm}
  \showanswers
   \end{questions}
\end{document}