我怎样才能让 beamer 的框架标题在所有情况下都顶部对齐？

Question

以下 MCE 指出，对于某些beamer主题，框架标题是垂直的：

• 在有（可能不可见的）框架字幕的情况下顶部对齐，
• 居中显示，无框架字幕。

我怎样才能使框架标题在所有情况下都顶部对齐？

\documentclass[9pt]{beamer}

\usetheme{PaloAlto}

\begin{document}

\begin{frame}
  \frametitle{Top aligned frame title if subtitle}
  \framesubtitle{Frame subtitle}
\end{frame}

\begin{frame}
  \frametitle{Top aligned frame title if (possibly invisible) subtitle}
  \framesubtitle{\mbox{}}
\end{frame}

\begin{frame}
  \frametitle{Vertically centered frame title if no frame subtitle}
\end{frame}

\end{document}

Answer 1

\strut您可以在frametitle模板中插入类似内容

\documentclass[9pt]{beamer}

\usetheme{PaloAlto}

\makeatletter
  \setbeamertemplate{frametitle}{%
    \nointerlineskip%
    \vskip-\beamer@headheight%
    \vbox to \beamer@headheight{%
      \vfil
      \leftskip=-\beamer@leftmargin%
      \advance\leftskip by0.3cm%
      \rightskip=-\beamer@rightmargin%
      \advance\rightskip by0.3cm plus1fil%
      {\usebeamercolor[fg]{frametitle}\usebeamerfont{frametitle}\insertframetitle\par}%
      {\usebeamercolor[fg]{framesubtitle}\usebeamerfont{framesubtitle}%
      \strut% NEW
      \insertframesubtitle\par}%
      \vbox{}%
      \vskip-1em%
      \vfil
    }%
  }
\makeatother

\begin{document}

\begin{frame}
  \frametitle{Top aligned frame title if subtitle}
  \framesubtitle{Frame subtitle}
\end{frame}

\begin{frame}
  \frametitle{Top aligned frame title if (possibly invisible) subtitle}
  \framesubtitle{\mbox{}}
\end{frame}

\begin{frame}
  \frametitle{Vertically centered frame title if no frame subtitle}
\end{frame}

\end{document}