How to insert "footline"-style page number into "headline"

Question

When inserting page numbers into beamer slides, I usually use:

\setbeamertemplate{footline}[page number]

Is it possible to do this for headline, something like:

\setbeamertemplate{headline}[page number]

Answer 1

Sure, it's not installed by default, but you do something like this:

\defbeamertemplate{headline}{page number}{%
    \vskip1pt%
    \setbeamertemplate{footline}[page number]%
    \usebeamertemplate{footline}%
}
\setbeamertemplate{headline}[page number]

Since the footline template is set inside the group it's not affected by your global theme. You can have a regular footline that's something else like infolines--although I assume you don't want that one because it's already got the page number in it.

This does seem to clobber the headline in some of the fancier themes. So you might try instead \addtobeamertemplate:

\addtobeamertemplate{headline}{%
    \vskip1pt%
    \setbeamertemplate{footline}[page number]%
    \setbeamercolor{page number in head/foot}{use=headline,fg=headline.fg,bg=headline.bg}
    \usebeamertemplate{footline}%    
}{% don't add anything after
}