根据部分和小节环境在框架中显示投影仪标题

Question

首先：该\section指令（在标准 LaTeX 中）不会启动环境。但是，您有点预见到您需要根据上一条更改界面。至少我的解决方案需要将部分分组到环境内。

条件逻辑最终并没有那么复杂。假设你有两个条件\ifinsertsection和\ifinsertsubsection。然后它们简单地嵌套在标题设置中，就像

\setbeamertemplate{headline}{%
  \ifinsertsection
    <do section headline>
    \ifinsertsubsection
      <do subsection headline>
    \fi
  \fi
}

现在实际的工作仍然是切换开关。第一个相当简单，因为当一个部分开始时它必须是 true。为此，您可以说

\let\ltx@section\section
\def\section{\insertsectiontrue\ltx@section}

或者采用环境方法：

\newenvironment{customsectionenv}[2][]{%
  \insertsectiontrue
  \section[#1]{#2}
}{}

完整的解决方案将使用此方法的版本，不仅因为需要控制子部分切换，而且因为可以知道某个部分在何处结束。

现在，子部分切换将与部分切换位于同一位置，但只有当部分主体至少包含一个时才应切换\subsection，如所要求。为此，您需要收集节环境的主体，将其存储到宏中（这包的用例environ）并扫描环境中的替换文本是否\BODY包含任何\subsection，可以通过以下方式解决这使用该包的问题substr：

\IfSubStringInString{\detokenize{\subsection}}{\detokenize\expandafter{\BODY}}
    {\insertsubsectiontrue}{}

完整的代码如下

\documentclass[handout]{beamer}

%Define colors
\definecolor{black}{RGB}{0,0,0}
\definecolor{darkblue}{RGB}{0,41,103}
\definecolor{lightblue}{RGB}{0,118,188}

\setbeamercolor*{section in head/foot}{fg=white, bg=lightblue}
\setbeamercolor*{section in head/foot shaded}{fg=white, bg=darkblue}
\setbeamercolor{subsection in head/foot}{fg=white, bg=darkblue}

\usepackage{environ,substr}% required for the solution

%Create headline environment
\newif\ifinsertsection
\newif\ifinsertsubsection

\NewEnviron{beamersection}[2][]{%
  \IfSubStringInString{\detokenize{\subsection}}{\detokenize\expandafter{\BODY}}
    {\insertsubsectiontrue}{}
  \insertsectiontrue
  \if\relax\detokenize{#1}\relax
    \section{#2}
  \else
    \section[#1]{#2}
  \fi
  \par\BODY
}

\setbeamertemplate{headline}{%
  \ifinsertsection
    \begin{beamercolorbox}[colsep=1.5pt]{upper separation line head}
    \end{beamercolorbox}
    \begin{beamercolorbox}{section in head/foot}
      \vskip2pt\insertsectionnavigationhorizontal{\paperwidth}{}{\hfill\hfill}\vskip2pt
    \end{beamercolorbox}%
    \ifinsertsubsection
      \begin{beamercolorbox}[ht=10pt]{subsection in head/foot}%
        \vskip2pt\insertsubsectionnavigationhorizontal{\paperwidth}{}{\hfill\hfill}\vskip2pt
      \end{beamercolorbox}%
      \begin{beamercolorbox}[colsep=1.5pt]{lower separation line head}
      \end{beamercolorbox}
    \fi
  \fi
  \vspace{20pt}
}

\begin{document}

\frame{%
  \frametitle{Frame outside section environment} 
  This frame should display neither the section, nor the subsection portion of the headline 
}

\begin{beamersection}{Section 1 (no subsections)}
\frame{%
  \frametitle{Frame in section environment with no subsections} 
  This frame should display the section portion of the headline, but not the subsection portion 
}
\end{beamersection}

\begin{beamersection}{Section 2 (with subsection)}
\subsection{Subsection 2.1}
\frame{%
  \frametitle{Frame in section environment (post-subsection)} 
  This frame should display both the section and subsection portions of the headline 
}
\end{beamersection}

\begin{beamersection}{Section 3 (with subsections)}
\frame{%
  \frametitle{Frame in section environment pre-subsection} 
  This frame should display both the section and subsection portions of the headline 
}
\subsection{Subsection 3.1}
\frame{%
  \frametitle{Frame in section environment post-subsection} 
  This frame should display both the section and subsection portions of the headline 
}
\end{beamersection}

\end{document}

几点说明：

我取消了第四个案例/部分。它相当于第三个案例/部分。
如上所述，使用此解决方案时，各部分的用户界面会发生变化；各部分将被编码为\begin{beamersection}[<opt. TOC title>]{<full title>} ... \end{beamersection}
输出图片由\usepackage{pgfpages}\pgfpagesuselayout{2 on 1}[letterpaper,border shrink=5mm]

Answer 1