如何在框架中保存布尔值？

Question

我的布尔变量管理在article类中或在单个框架内有效，但在从一个框架到另一个框架时却不起作用，为什么？

\documentclass{beamer}
\usepackage{tikzducks}
\usepackage{ifthen}
\newboolean{toleft}
\setboolean{toleft}{false}     
\newcommand{\duckfamily}[1][1]{%
    \begin{center}
        \begin{tikzpicture}[xscale=#1]
        \begin{scope}[scale=.15]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+10pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+20pt, scale=.1]
        \duck
        \end{scope}
        \end{tikzpicture}
    \end{center}
}

\newcommand{\duckdecor}{%
    \ifthenelse{\boolean{toleft}}{%
        \duckfamily
        \setboolean{toleft}{false}
        }{%
        \duckfamily[-1]
        \setboolean{toleft}{true}
        } 
}

\begin{document}
\begin{frame}
    I would like to type this decor:
    \duckdecor
    alternatively from right to left
    \duckdecor
    and from left to right
    \duckdecor
\end{frame}
\begin{frame}
    But if it is in different frames\dots  
    \duckdecor
\end{frame}
\begin{frame}
    \dots it doesn't work.
    \duckdecor
\end{frame}
\begin{frame}
    Why?
    \duckdecor
\end{frame}
\end{document}

Answer 1

etoolbox 具有布尔命令，您可以将其加上前缀 \global：

\documentclass{beamer}
\usepackage{tikzducks}
\usepackage{etoolbox} %already loaded by beamer
\newbool{toleft}
\global\booltrue{toleft}
\newcommand{\duckfamily}[1][1]{%
    \begin{center}
        \begin{tikzpicture}[xscale=#1]
        \begin{scope}[scale=.15]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+10pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+20pt, scale=.1]
        \duck
        \end{scope}
        \end{tikzpicture}
    \end{center}
}

\newcommand{\duckdecor}{%
    \ifbool{toleft}{%
        \duckfamily
        \global\boolfalse{toleft}
        }{%
        \duckfamily[-1]
        \global\booltrue{toleft}
        }
}

\begin{document}
\begin{frame}
    I would like to type this decor:
    \duckdecor
    alternatively from right to left
    \duckdecor
    and from left to right
    \duckdecor
\end{frame}
\begin{frame}
    But if it is in different frames\dots
    \duckdecor
\end{frame}
\begin{frame}
    \dots it doesn't work.
    \duckdecor
\end{frame}
\begin{frame}
    Why?
    \duckdecor
\end{frame}
\end{document}

Answer 2

我使用了 Jagath 的答案变量在环境之外持续存在，在序言开头添加4行并注释掉\usepackage{ifthen}。

\documentclass{beamer}
\usepackage{tikzducks}
%\usepackage{ifthen}
%
\def\boolean#1{#1}
\def\newboolean#1{\expandafter\newif\csname if#1\expandafter\endcsname\csname  #1false\endcsname}
\def\setboolean#1#2{\expandafter\global\csname #1#2\endcsname}
\def\ifthenelse#1#2#3{\csname if#1\endcsname#2\else#3\fi}
%
\newboolean{toleft}
\setboolean{toleft}{false}     
\newcommand{\duckfamily}[1][1]{%
    \begin{center}
        \begin{tikzpicture}[xscale=#1]
        \begin{scope}[scale=.15]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+10pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+20pt, scale=.1]
        \duck
        \end{scope}
        \end{tikzpicture}
    \end{center}
}

\newcommand{\duckdecor}{%
    \ifthenelse{\boolean{toleft}}{%
        \duckfamily
        \setboolean{toleft}{false}
        }{%
        \duckfamily[-1]
        \setboolean{toleft}{true}
        } 
}

\begin{document}
\begin{frame}
    I would like to type this decor:
    \duckdecor
    alternatively from right to left
    \duckdecor
    and from left to right
    \duckdecor
\end{frame}
\begin{frame}
    But if it is in different frames\dots  
    \duckdecor
\end{frame}
\begin{frame}
    \dots it doesn't work.
    \duckdecor
\end{frame}
\begin{frame}
    Why?
    \duckdecor
\end{frame}
\end{document}

重新定义 可能不是一个好的做法\ifthenelse，而是将其命名为，例如，\def\gifthenelse#1#2#3{\csname if#1\endcsname#2\else#3\fi}然后在宏\gifthenelse内部使用\duckdecor来代替\ifthenelse。

Answer 3

问题是，beamer 将框架的内容包装在一个组内，您会遇到同样的问题{ \duckdecor } \duckdecor。

解决方法：使用计数器而不是布尔值并测试计数器是奇数还是偶数。

\documentclass{beamer}
\usepackage{tikzducks}

\newcommand{\duckfamily}[1][1]{%
    \begin{center}
        \begin{tikzpicture}[xscale=#1]
        \begin{scope}[scale=.15]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+10pt, scale=.1]
        \duck
        \end{scope}
        \begin{scope}[xshift=14pt+20pt, scale=.1]
        \duck
        \end{scope}
        \end{tikzpicture}
    \end{center}
}

\newcounter{test}
\setcounter{test}{1}

\newcommand{\duckdecor}{%
    \addtocounter{test}{1}%
    \ifodd\value{test}%
        \duckfamily%
    \else%
        \duckfamily[-1]%
    \fi%
}

\begin{document}

\begin{frame}
    \duckdecor
\end{frame}

\begin{frame}
    \duckdecor
\end{frame}

\end{document}