Add command at the beginning of all frames

Question

I need to add a command \setRTL from the bidi package to write right-to-left text, at the beginning of every frame.

Another answer does not solve the issue; any suggestions?

\documentclass{beamer} 
\usefonttheme{serif}
\usetheme{Madrid}

\usepackage{etoolbox}  % no longer needed; loaded by Beamer from v3.36

\usepackage{bidi}

\AtBeginEnvironment{frame}{\setRTL}

\begin{document}
    \begin{frame}{frame title}
        hello world

        \begin{enumerate}
            \item first item
            \item second item
        \end{enumerate}
    \end{frame}
\end{document}

Answer 1

You cannot directly hook into the begin of Beamer's frame environment with the usual etoolbox \AtBeginEnvironment, as hinted at elsewhere.

Replacing your \AtBeginEnvironment with \BeforeBeginEnvironment, is actually sufficient. That is:

\BeforeBeginEnvironment{frame}{\setRTL}

This may, however, have undesirable side-effects, since it hooks in prior to the environment's definition.

One alternative is the following (hooking into @checkframetitle), adapted from another similar answer, however it will not affect the slide's title:

\makeatletter
    \pretocmd\beamer@checkframetitle{\setRTL}
\makeatother

Finally, you could instead hook into the earlier @framenotesbegin, which would affect the slide title (obtaining an equivalent result to the \BeforeBeginEnvironment approach):

\makeatletter
    \pretocmd\beamer@framenotesbegin{\setRTL}
\makeatother