Have multiple overlay items at the same position

Question

I want to have a list of items on a beamer slid which should appear one by one. For each item, I want to have a separate explanation block which should only be visible as the item appears. What I have is this code:

\begin{frame}
  \begin{itemize}
      \item<1-> Foo
      \item<2-> Bar
      \item<3-> Bla
  \end{itemize}
  \begin{block}{About Foo}<1>
    ...
  \end{block}
  \begin{block}{About Bar}<2>
    ...
  \end{block}
  \begin{block}{About Bla}<3>
    ...
  \end{block}
\end{frame}

This does work, but my problem is, that the three blocks are below each other. They get their fixed position as if I was not using overlays and just get hidden.

What I want is the three blocks to be all on the same position (the one of the About Foo block). Is that possible?

Answer 1

You can warp your blocks in onlyenv to get the desired result:

\documentclass{beamer}

\begin{document}

\begin{frame}
  \begin{itemize}[<+->]
      \item Foo
      \item Bar
      \item Bla
  \end{itemize}
  \begin{onlyenv}<1>
      \begin{block}{About Foo}
        ...
      \end{block}
  \end{onlyenv}
  \begin{onlyenv}<2>
      \begin{block}{About Bar}
        ...
      \end{block}
  \end{onlyenv}
  \begin{onlyenv}<3>
      \begin{block}{About Bla}
        ...
      \end{block}
  \end{onlyenv}    
\end{frame}

\end{document}