Beamer: Correct vertical alignment using \only

Question

I'll get straight to the point. MWE:

\documentclass{beamer}
\usetheme{metropolis}

\begin{document}

\begin{frame}[t]{title}
\begin{itemize}
    \item 0
    \only<+>{
        \item a
    }
    \only<+>{
        \item b
        \item c
    }
    \only<+>{
        \item d
        \item e
        \item f
        \item 
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
    }
\end{itemize}
\end{frame}
\end{document}

I.e. 0 stays at the top all the time, a is on the first slide then leaves, b and c come and leave on slide two and so forth.

The problem is, that d-g are very long and thus on the third slide item 0 floats very slightly to the top (less than say 0.5em). However, I still have enough space at the bottom of the slide to not have this happen. Frame option [t] does not seem to help. This is super irritating as the third slide seems to be something totally new to the eye at first.

I'm sure there is a very easy fix to this. I appreciate any help. Many thanks!

Answer 1

You can solve this problem by wrapping the whole itemization in an overlay area which is height enough to accommodate even the items with the long text:

\documentclass{beamer}
\usetheme{metropolis}

\begin{document}

\begin{frame}[t]{title}
\begin{overlayarea}{\textwidth}{.86\textheight}
\begin{itemize}
    \item 0
    \only<+>{%
        \item a
    }
    \only<+>{%
        \item b
        \item c
    }
    \only<+>{%
        \item d
        \item e
        \item f
        \item 
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
        ggggggggggggggggggggggggggggggggggggggggg
    }
\end{itemize}
\end{overlayarea}
\end{frame}
\end{document}