Footnote rule in beamer showing too early with overlays

Question

Consider the following MWE :

\documentclass{beamer}

\begin{document}

\begin{frame}

\begin{itemize}[<+->]
\item item
\item item\footnote<.->{footnote}
\item item
\end{itemize}

\end{frame}

\end{document}

The horizontal rule which is displayed between the main text and the footnote is showing on the first slide, although the footnote itself is uncovered only on the second slide.

Is there a way for this rule to be printed only with the footnote and not before?

Answer 1

This rule is not part of the \footnote command but the frame with footnotes. It's drawn with \footnoterule command within \beamer@autobreakframebox in file beamerbaseframesize.sty. When beamer computes frame dimensions it considers if frame has footnotes and draws the rule in this case.

The best solution I can provide is not draw the rule at all. Next code includes a copy of \beamer@autobreakframebox in your file with a commented \footnoterule command. I don't know if this solution will work with other themes (I hope so).

\documentclass{beamer}

\makeatletter
\def\beamer@autobreakframebox{%
  \global\setbox\beamer@splitbox=\box\voidb@x%
  \ifbeamer@autobreak%
    % Ok, frame was overful -> split it!
    \setbox\@tempboxa=\vsplit\beamer@framebox to\beamer@autobreakfactor\textheight%
    \global\setbox\beamer@splitbox=\box\beamer@framebox%
    \@tempdima=\ht\beamer@splitbox%
    \ifdim\@tempdima<\beamer@autobreaklastheight%
      \global\beamer@autobreaklastheight=\@tempdima\relax%
    \else%
      \setbox\@tempboxa=\vbox{\unvbox\@tempboxa\unvbox\beamer@splitbox}%
      \global\setbox\beamer@splitbox=\box\voidb@x%
    \fi%
    \setbox\beamer@framebox=\vbox to\textheight{\unvbox\@tempboxa%
      \vskip\beamer@framebottomskipautobreak%
      \ifvoid\beamer@splitbox%
        \ifvoid\beamer@footins%
        \else%
          \begingroup
            \usebeamercolor*[fg]{footnote}%
%            \footnoterule%
            \unvbox \beamer@footins%
            \global\setbox\beamer@footins=\box\voidb@x%
          \endgroup  
        \fi%
      \fi%
      \beamer@exitcode%
    }%
  \else%
    \setbox\beamer@framebox=\vbox to\textheight{\unvbox\beamer@framebox%
      \vskip\beamer@framebottomskip%
      \ifvoid\beamer@footins%
      \else%
        \begingroup
          \usebeamercolor*[fg]{footnote}%
%         \footnoterule%
          \unvbox \beamer@footins%
          \global\setbox\beamer@footins=\box\voidb@x%
        \endgroup 
      \fi%
      \beamer@exitcode}%
    \global\setbox\beamer@footins=\box\voidb@x%
  \fi%
  }
\makeatother
\begin{document}

\begin{frame}

\begin{itemize}[]
\item<1-> item
\item<2-> {item\footnote<2->{footnote}}
\item<3-> item
\end{itemize}

\end{frame}

\end{document}