\includegraphics within braces with metropolis beamer theme: image doesn't appear

Question

I am using the Metropolis theme in beamer, and wondering why having \includegraphics within braces {...} doesn't work (image doesn't get added in). I get a blank slide (with title) with the code below:

\documentclass[10pt]{beamer}
\usetheme[progressbar=frametitle]{metropolis}
\begin{document}
\begin{frame}{test}
{\hfill\includegraphics[width=1cm]{example-image}\hfill}
\end{frame}
\end{document}

Commenting out the metropolis line, (thus, switching to using the default beamer theme), the image appears as expected. So I know this behaviour has something to do with the metropolis theme.

I know I can remove the braces, but you can imagine a scenario where I want some effect localized/grouped, e.g. \color{blue}. I want to know why does this happen?

Answer 1

It's not a problem with beamer-metropolis, it's a problem with your code.

beamerdefines this syntax \begin{frame}{frame title}{frame subtitle} where title and subtitle are optionals. Therefore your figure is considered as a subtitle, but metropolis has no subtitle commands, then it's ignored.

Compare this

\documentclass[10pt]{beamer}
\begin{document}
\begin{frame}{test}
{\hfill\includegraphics[width=1cm]{example-image}\hfill}
\end{frame}
\end{document}

with this:

\documentclass[10pt]{beamer}
\begin{document}
\begin{frame}{test}

{\hfill\includegraphics[width=1cm]{example-image}\hfill}
\end{frame}
\end{document}

As you can see, even without metropolis your syntax does not produce the expected result.

If you don't want to leave an empty line between title and contents, use this alternative syntax (or at least don't start new line with '{')

\documentclass[10pt]{beamer}
\usetheme[progressbar=frametitle]{metropolis}
\begin{document}
\begin{frame}{test}
\centerline{\includegraphics[width=1cm]{example-image}}
%{\hfill\includegraphics[width=1cm]{example-image}\hfill}
\end{frame}
\end{document}