Allow theorem split in many frames in beamer

Question

How can a theorem-like environment be (automatically) split into multiple frames if the vertical space it needs is not enough in a frame?

In my document preamble I have

\theoremstyle{definition}
\newtheorem{exercise}{Exercício}

And a given frame in the document has an exercise environment which does not fit into a single frame. So I want it split in more frames.

Any clues?

Answer 1

Generally you can use the beamer option allowframebreaks to split a frame automatically if its content doesn't fit on one frame:

\begin{frame}[allowframebreaks]
  ...
\end{frame}

Sadly, this doesn't work for theorem-like environments, the reason being that these are typeset using a beamercolorbox by default. The contents of a beamercolorbox are gathered in one single box which can't be split across frames.

I only see two possibilities to overcome this at the moment:

1. Make the theorem environments not use a beamercolorbox for the content. This can be done by redefining the beamer templates theorem begin and theorem end:

   \documentclass{beamer}
   \theoremstyle{definition}
   \newtheorem{exercise}{Exercício}
   \setbeamertemplate{theorem begin}
   {%
     \par\vskip\medskipamount%
     \begin{beamercolorbox}[colsep*=.75ex]{block title}
       \usebeamerfont*{block title}%
         \inserttheoremname
         \ifx\inserttheoremaddition\empty\else\ (\inserttheoremaddition)\fi%
     \end{beamercolorbox}%
     {\parskip0pt\par}%
     \ifbeamercolorempty[bg]{block title}
     {}
     {\ifbeamercolorempty[bg]{block body}{}{\nointerlineskip\vskip-0.5pt}}%
     \usebeamerfont{block body}%
     \vskip-.25ex\vbox{}%
   }
   \setbeamertemplate{theorem end}{}
   \usepackage{lipsum}
   \begin{document}
   \begin{frame}[allowframebreaks]
   \begin{exercise}
   \lipsum[1]
   \lipsum[2]
   \end{exercise}
   \end{frame}
   \end{document}
   

   _{(The lipsum is for creating dummy text, you can remove it and replace it with your own content.)}

   Note however, that this may considerably change the look of your theorems if you use a theme that has a colored background for theorems. For sober themes like the default one or Montpellier it should be perfectly fine.

2. You can manually issue the frame breaks. To do this, define a new macro \theorembreak that ends the current beamercolorbox, starts a new frame and a new beamercolorbox:

   \documentclass{beamer}
   \theoremstyle{definition}
   \newtheorem{exercise}{Exercício}
   \newcommand*{\theorembreak}{\usebeamertemplate{theorem end}\framebreak\usebeamertemplate{theorem begin}}
   \usepackage{lipsum}
   \begin{document}
   \begin{frame}[allowframebreaks]
   \begin{exercise}
   \lipsum[1]
   \theorembreak
   \lipsum[2]
   \end{exercise}
   \end{frame}
   \end{document}
   

   

   This has the advantage that you can keep the exact style of your theorems, but forces you to do the breaking manually.

Answer 2

Since the theorem-like structures use a beamercolorbox, using allowframebreaks option directly won't work in this case. A workaround would be to "simulate" your theorem-like heading with a beamercolorbox and then write the text outside the box with the allowframebreaks option:

\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usepackage{lipsum}

\begin{document}

\begin{frame}[allowframebreaks=0.8]

\begin{beamercolorbox}{section in head/foot}
Exercício
\end{beamercolorbox}{}
\lipsum[1-2]
\end{frame}

\end{document}