计数器的问题

Question

在尝试回答问题时，我遇到了计数器问题，我需要一些帮助。这个想法是收集一些编号练习的答案，这样收集到的答案就可以在文档的稍后时间全部排版；我的方法是使用collect打包来收集答案：

\documentclass{scrartcl}
\usepackage{collect}

\definecollection{answers}

\makeatletter
\newenvironment{answer}
  {\@nameuse{collect}{answers}%
    {\par\medskip\noindent\textbf{Answer to~\theexercise}}%
    {\par}%
    {}%
    {}%
  }
  {\@nameuse{endcollect}}
\makeatother

\newcounter{exercise}
\newenvironment{ex}
  {\refstepcounter{exercise}\par\noindent This is exercise~\theexercise}
  {\par}

\begin{document}

\begin{ex}
\end{ex}
\begin{answer}
This is the answer to exercise 1 but it is numbered 3.
\end{answer}

\begin{ex}
\end{ex}
\begin{answer}
This is the answer to exercise 2 but it is numbered 3.
\end{answer}

\begin{ex}
\end{ex}
\begin{answer}
This is the answer to exercise 3 and it is numbered 3.
\end{answer}

\includecollection{answers}

\end{document}

然而，正如预期的那样，使用这种方法，所有答案都会收到与计数器最后一个值相对应的数字exercise，而不是与它们对应的练习相关的数字（见图）。如何解决这个问题？

Answer 1

\theexercise在进行写入之前您必须进行扩展：

\documentclass{scrartcl}
\usepackage{collect}

\definecollection{answers}

\newcommand\mycollect[1]{%
  \collect{answers}
    {\par\medskip\noindent\textbf{Answer to~#1}}
    {\par}
    {}{}%
}

\newenvironment{answer}
  {\begingroup\edef\x{\endgroup\noexpand\mycollect{\theexercise}}\x}
  {\endcollect}

\newcounter{exercise}
\newenvironment{ex}
  {\refstepcounter{exercise}\par\noindent This is exercise~\theexercise}
  {\par}

\begin{document}

\begin{ex}
\end{ex}
\begin{answer}
This is the answer to exercise 1 but it is numbered 3.
\end{answer}

\begin{ex}
\end{ex}
\begin{answer}
This is the answer to exercise 2 but it is numbered 3.
\end{answer}

\begin{ex}
\end{ex}
\begin{answer}
This is the answer to exercise 3 and it is numbered 3.
\end{answer}

\includecollection{answers}

\end{document}