I was reading the answer to this question Mixing overprint with blocks of enumerations
[I recopy the code so you dont' have to follow the link]
\documentclass{beamer}
\usetheme{Warsaw}
\begin{document}
\begin{frame}{Test}
\begin{center}
text before
\pause
\begin{overlayarea}{\textwidth}{3.3cm}
\only<2-3>{%
\begin{block}{Some title here}
\begin{enumerate}[<+->]
\item One
\item Two
\end{enumerate}
\end{block}}
\only<4-7>{%
\begin{block}{Some title here}
\begin{enumerate}[<+(2)->]
\item CHicken
\item Duck
\item Rooster
\end{enumerate}
\end{block}}
\end{overlayarea}
text after
\end{center}
\end{frame}
\end{document}
and I noticed the use of a number between parentheses in the default incremented overlay specification in the second enumerate
environment. (see the presence of [<+(2)->]
) Only then will the items of the second numbered list in the overlayarea
environment be uncovered incrementally.
Why is that needed ? It seems to imply that beamerpauses
is reset between the enumerate
environments ? Or is it reset between the only
commands in the overlay
environment?
Isnt that a nasty behaviour? Because it is as if you are supposed to keep track yourself of beamerpauses. The usefulness of [<+->]
is lost then, isn't it ?
Best Answer
The apparently odd phenomenon can be explained examining the following simple example:
After processing the document you'll have a three slide presentation showing the value of the
beamerpauses
counter at different stages.Up to slide two, everything goes as one would expect: at the end of the
enumerate
on slide two the value ofbeamerpauses
is three; however, on slide three,beamerpauses
is1
. Why happened this? Well, because the overlay specification for\only
was1-2
, so everything happening on slides 1 and 2 will occur only for those slides; in particular, the stepping ofbeamerpauses
produced by the enumerate will have effect only for slides one and two. In the third slide, which is not under the effect of the\only
, the counterbeamerpauses
will have the value that it had before.Is this showing something wrong with
beamer
? I don't think so; after all, the expected meaning of\only
is to keep things under its scope only for the specified slides.If you use
<1->
(or<1-3>
) instead of<1-2>
in the above example, as inyou'll see that now on slide three the counter has the value three, because the third slide is under the scope of
\only
.The "dirty" manual increment of the counter in the original example was simply due to the special effect the OP wanted to achieve. Perhaps this same effect could be achieved in another way, without manual intervention?