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範圍或覆蓋 \pause？

tag-icon • tag-icon beamer align pause
範圍或覆蓋 \pause？

我有一些包含多部分問題的講座幻燈片。我希望學生能夠看到整個問題的佈局，然後逐步填寫答案。只要填滿的內容可以分成漂亮的小塊，這是可行的：

\documentclass{beamer}
\begin{document}

\begin{frame}\onslide<+->{}
This problem has three parts.
  \begin{enumerate}
    \item What is the answer to part 1?\\
      \onslide<+->{First interpret the question.}\onslide<+->{ Then do some work.}\onslide<+->{ Now we can answer the question, and the answer is} \onslide<+->{ 42.}
    \item What is the answer to part 2?\\
      \onslide<+->{This problem is easy, and the answer is }\onslide<+->{0.}
    \item What is the answer to part 3?\\
      \onslide<+->{You'll have to figure this one out for yourself.}
  \end{enumerate}
\end{frame}
\end{document}

這個解決方案相當優雅（除了最初\onslide<+->增加計數器之外）。不幸的是，如果我想在環境中間暫停（例如對齊），它就會崩潰（或至少變得非常混亂）：

\documentclass{beamer}
\usepackage{amsmath}
\begin{document}
%% Standard (?) fix to make \pause work at all in align environment
\mode<presentation>{\setbeamercovered{transparent=0}}
\makeatletter
\def\beamerorig@set@color{%
  \pdfliteral{\current@color}%
  \aftergroup\reset@color
}
\def\beamerorig@reset@color{\pdfliteral{\current@color}}
\makeatother
%%

\begin{frame}
This problem has three parts.
  \begin{enumerate}
    \item What is the answer to part 1?\\\pause
      First interpret the question. Then calculate
      \begin{align*}
        \Pr[X\in A] &=\pause \frac{1}{2^n} \sum_{i=0}^n \binom{n}{i} \\ 
        &=\pause 1
      \end{align*}
    \item What is the answer to part 2?\\\pause
      More answers, \pause with more parts.
    \item What is the answer to part 3?\\\pause
      ...
  \end{enumerate}
\end{frame}
\end{document}

當然，如果我這樣做，問題的後面部分直到我們完成第一部分之後才會出現。

我可能可以通過將答案分解成更小的塊，然後確保前面的文本和第一部分align同時顯示來使前一種方法發揮作用，但這似乎需要根據具體情況進行大量手動調整- 案例基礎。我認為正確的解決方案是要么將 的影響限制\pause在答案本身的某個範圍內，要么通過強制我希望在開始時可見的後續材料不透明來覆蓋它（我相信修復已經align使其成為可能）這樣文本就始終存在，只是透明的）。

有沒有好的方法可以做到這一點？

答案1

我最終使用了以下解決方法，使用（誠然非常黑客）\always命令重置其內容的幻燈片計數器：

\documentclass{beamer}
\usepackage{amsmath}
%% Standard (?) fix to make \pause work at all in align environment
\mode<presentation>{\setbeamercovered{transparent=0}}
\makeatletter
\def\beamerorig@set@color{%
  \pdfliteral{\current@color}%
  \aftergroup\reset@color
}
\def\beamerorig@reset@color{\pdfliteral{\current@color}}
\makeatother
%%

%% \always{} command ensures that its contents are visible on all slides of the frame.
\newcounter{beamerpausessave}
\newcommand{\always}[1]{\setcounter{beamerpausessave}{\value{beamerpauses}}
    \setcounter{beamerpauses}{0}\pause #1 
    \setcounter{beamerpauses}{\value{beamerpausessave}}\addtocounter{beamerpauses}{-1}\pause}

\begin{document}
\begin{frame}
This problem has three parts.
  \begin{enumerate}
    \always{\item What is the answer to part 1?\\}\pause
      First interpret the question. Then calculate
      \begin{align*}
        \Pr[X\in A] &=\pause \frac{1}{2^n} \sum_{i=0}^n \binom{n}{i} \\ 
        &=\pause 1
      \end{align*}
    \always{\item What is the answer to part 2?\\}\pause
      More answers, \pause with more parts.
    \always{\item What is the answer to part 3?\\}\pause
      ...
  \end{enumerate}
\end{frame}

\end{document}

我仍然不太明白為什麼在沒有更簡單的方法的情況下，設定beamerpauses和使用的特定組合\pause會起作用。

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