Problems with counters and frame splitting commands and environments in beamer

Question

Using the package gb4e for linguists in the beamer environment in combination with frame splitting commands \pause or environments overprint, I face the following problem: The number are "jumping" strangely.

The same happens when I use the beispiel environment (see below) in combination with \pause command or the splitting environments. Therefore, I believe, that it is a general problem of a certain kind of counters with these commands and environments. My question is: How do I avoid this odd jumping behaviour? (In regard to the gb4e based environment the answer is more important. The other I just provided to show the general nature of this problem. However, I would like to see a possible solution here as well, to get a deeper understanding of LaTeX.)

\documentclass{beamer}
%\usetheme{Bergen}

\usepackage[ngerman]{babel} %dt. Silbentrennung
\usepackage[applemac]{inputenc}

  \usepackage{gb4e}

  \newcounter{beispz} %Beispiele mit durchgehender Nummerierung und  in italics
\newenvironment{beispiel}
    {\stepcounter{beispz}
    \begin{enumerate}\item[(\arabic{beispz})]\linespread{1}\em}
    {\end{enumerate}} %\label{\stepcounter{beispz}}

\begin{document}

\begin{frame}
\begin{exe}
\ex Du bist mir ein feiner Freund!\pause
\ex A: Wie viele Einwohner hat New York?
\end{exe}
\end{frame}

\begin{frame}
\begin{beispiel} asdfas\end{beispiel} \pause

\begin{beispiel} hand\end{beispiel}
\end{frame}

\end{document}

Remark: Werner gave a possible solution. It involves manually setting the counter number by adding \addtocounter{}{+previous no} in front of the counting environment and using \addtocounter{}{-last no} in the end of the environment (see below). For example:

\begin{beispiel}a\end{beispiel}\pause \begin{beispiel}b\end{beispiel}\addtocounter{beispz}{-2}\pause.

It works. But

As you can imagine, it involves a great deal of manual work if you are preparing a larger document. Therefore, I would like to ask if there is anyone out there who knows a solution that needs considerably less effort.

Answer 1

beamer does a lot of legwork in the background when you use the \pause command. In fact, to maintain the correct vertical/horizontal alignment, it still has to process whatever is presented after \pause, even though it is not printed on that particular slide. As such, it also parses the contents, incrementing counters as it going along. The following exaggerates this problem, but acts as a prime example:

\documentclass{beamer}% http://ctan.org/pkg/beamer
\begin{document}
\newcounter{beispz} %Beispiele mit durchgehender Nummerierung und  in italics
\newenvironment{beispiel}
  {\stepcounter{beispz}
   \begin{enumerate}\item[(\arabic{beispz})]\linespread{1}\em}
  {\end{enumerate}} %\label{\stepcounter{beispz}}

\begin{document}
\begin{frame}
\begin{beispiel} abc\end{beispiel} \pause
\begin{beispiel} def\end{beispiel}
\begin{beispiel} ghi\end{beispiel}
\begin{beispiel} jkl\end{beispiel}
\end{frame}

\end{document}​

Slide 1 only sets (1) abc with the correct counter. However, it also processes the remaining beispiel environment on slide 1, leaving the beispz counter at 4 at the end of slide 1. Then it reprocesses the frame to produce the second slide, this time starting with (5) abc, as expected.

To avoid this, you have to know which counters are being manipulated and compensate for them via \addtocounter{<cntr>}{<num>}. Here is you example, modified to match with the correct layout:

\documentclass{beamer}% http://ctan.org/pkg/beamer
\usepackage{gb4e}% http://ctan.org/pkg/gb4e

\newcounter{beispz} %Beispiele mit durchgehender Nummerierung und  in italics
\newenvironment{beispiel}
  {\stepcounter{beispz}
   \begin{enumerate}\item[(\arabic{beispz})]\linespread{1}\em}
  {\end{enumerate}} %\label{\stepcounter{beispz}}

\begin{document}

\begin{frame}
\begin{exe}
  \ex Du bist mir ein feiner Freund!\pause
  \ex A: Wie viele Einwohner hat New York? \addtocounter{xnumi}{-2}
\end{exe}
\end{frame}

\begin{frame}
\begin{beispiel} abc\end{beispiel} \pause
\begin{beispiel} def\end{beispiel} 
\begin{beispiel} ghi\end{beispiel}
\begin{beispiel} jkl\end{beispiel} \addtocounter{beispz}{-4}
\end{frame}
\end{document}​

The counter associated with the first environment exe is xnumi (from looking at the source code of gb4e), while that of the second beispiel is, of course, beispz.