引用投影仪幻灯片编号时并非所有幻灯片都显示（未定义的引用错误）

Question

我有一张逐渐打开的幻灯片。假设它通常有 n 张幻灯片。但是“现在”我决定不从幻灯片 1 开始，而是从幻灯片 2 开始。尽管仍然显示了 n-1 张幻灯片，但 LaTeX 仍然认为它无法再找到标签定义！我该如何解决这个问题？

下面我提供了一个最小的例子。请注意，我复制了所有幻灯片，这样我就可以定义标签作为幻灯片的参数，也可以以“通常的方式”定义标签——只是为了表明这不会改变任何东西。

这里是代码：

\documentclass{beamer}

\begin{document}

\begin{frame}<2->{Title of Slide 1}\label{LabelOfSlideOne}
  Slide 1 has three subslides, opened one by one, normally. Here, however, we start at slide number 2!
  \begin{itemize}[<+->]
    \item 1
    \item 2
    \item 3
  \end{itemize}
\end{frame}


\begin{frame}<2->[label=LabelOfSlideTwo]{Title of Slide 2}
  Slide 2 is exactly as slide 1, we simply define the label differently.
  \begin{itemize}[<+->]
    \item 1
    \item 2
    \item 3
  \end{itemize}
\end{frame}


\begin{frame}{Title of Slide 3}\label{LabelOfSlideThree}
  Slide 3 has two subslides, we show them incrementally, as normal.
  \begin{itemize}[<+->]
    \item 1
    \item 2
  \end{itemize}
\end{frame}


\begin{frame}[label=LabelOfSlideFour]{Title of Slide 4}
  Slide 4 is exactly as slide 3, we simply define the label differently.
  \begin{itemize}[<+->]
    \item 1
    \item 2
  \end{itemize}
\end{frame}


\begin{frame}{Slide 5: Test all the references!}
  \begin{itemize}
    \item This should show a 1: \ref{LabelOfSlideOne}
    \item This should show a 2: \ref{LabelOfSlideTwo}
    \item This should show a 3: \ref{LabelOfSlideThree}
    \item This should show a 4: \ref{LabelOfSlideFour}
  \end{itemize}
\end{frame}

\end{document}

这就是结果：

这表明通常情况下定义标签可以完美运行（最后两张幻灯片），但当我们不显示所有幻灯片时（前两张幻灯片），它不起作用。

那么...如何解决这个问题？

Answer 1

有几种方法可以避免这个问题：

• 您可以在特定的覆盖层上指定标签，例如\label<2>{LabelOfSlideOne}

• 您可以引用标签的特定覆盖，例如\ref{LabelOfSlideTwo<2>}

---

\documentclass{beamer}

\begin{document}

\begin{frame}<2->{Title of Slide 1}\label<2>{LabelOfSlideOne}
  Slide 1 has three subslides, opened one by one, normally. Here, however, we start at slide number 2!
  \begin{itemize}[<+->]
    \item 1
    \item 2
    \item 3
  \end{itemize}
\end{frame}


\begin{frame}<2->[label=LabelOfSlideTwo]{Title of Slide 2}
  Slide 2 is exactly as slide 1, we simply define the label differently.
  \begin{itemize}[<+->]
    \item 1
    \item 2
    \item 3
  \end{itemize}
\end{frame}


\begin{frame}{Title of Slide 3}\label{LabelOfSlideThree}
  Slide 3 has two subslides, we show them incrementally, as normal.
  \begin{itemize}[<+->]
    \item 1
    \item 2
  \end{itemize}
\end{frame}


\begin{frame}[label=LabelOfSlideFour]{Title of Slide 4}
  Slide 4 is exactly as slide 3, we simply define the label differently.
  \begin{itemize}[<+->]
    \item 1
    \item 2
  \end{itemize}
\end{frame}


\begin{frame}{Slide 5: Test all the references!}
  \begin{itemize}
    \item This should show a 1: \ref{LabelOfSlideOne}
    \item This should show a 2: \ref{LabelOfSlideTwo<2>}
    \item This should show a 3: \ref{LabelOfSlideThree}
    \item This should show a 4: \ref{LabelOfSlideFour}
  \end{itemize}
\end{frame}

\end{document}