Getting an optional title with nameref and xparse

Question

Suppose I defined an environment with an optional argument (using xparse) as in

\documentclass{article}
\usepackage{hyperref,xparse}
\newcounter{exercisecounter}
\stepcounter{exercisecounter}
\DeclareDocumentEnvironment{exercise}{o}
{\IfNoValueTF{#1}{Exercise \theexercisecounter:}{Exercise \theexercisecounter (#1):}}
{}
\begin{document}
\begin{exercise}[My Exercise]
This is my exercise.
\end{exercise}
Above is \nameref{my exercise}, which is Exercise \ref{my exercise}.
\end{document}

If I'd like to reference the exercise's title and the exercise counter using nameref and ref, respectively, how would I go about doing it? In general, given an arbitrary environment with an optional argument, how would I got about telling hyperref to use the optional argument as the title and a specified counter?

I understand that a solution would likely be based on using xpatch, but this is the extent of my knowledge.

Answer 1

You have to set the title using nameref's \NR@gettitle macro:

\documentclass{article}
\usepackage{hyperref,xparse}% hyperref also loads nameref
\newcounter{exercisecounter}
\makeatletter
\DeclareDocumentEnvironment{exercise}{o}
  {\par\refstepcounter{exercisecounter}%
   Exercise \theexercisecounter
   \IfNoValueF{#1}{ (#1)\NR@gettitle{#1}}%
   :\quad}
  {\par}
\makeatother
\begin{document}
\begin{exercise}[My Exercise]
This is my exercise.\label{my exercise}
\end{exercise}
Above is \nameref{my exercise}, which is Exercise \ref{my exercise}.
\end{document}

Also note, for reference purposes, you need \refstepcounter (inside the environment). Also, the above setup doesn't do much when you don't supply an optional argument. That can be adopted, but then again you won't use \nameref when it doesn't have an optional argument...