如何在 itemize 环境中测量项目的宽度？

Question

我希望下面代码的输出像这张图片一样。怎么做？
请记住，[Foo Bar Foo] 的宽度是可变的。所以它应该自动计算。

\documentclass{book}
\begin{document}
\noindent Just enough text to make the line break so we get to see a second line.
\begin{itemize}
  \item[Foo] An item
  \item[Foo Bar Foo] An item An item An item An item An item An item An item An item An item An item An item An item An item An item  
  \item[Bar Bar] An item 
\end{itemize}
Just enough text to make the line break so we get to see a second line.
\end{document}

编辑：我不想使用表格或类似的环境，因为有许多项目应该跨越一些页面。

Answer 1

如果的主体中没有标签或计数器设置（例如编号方程式）等危险的东西itemize，您可以本地重新定义\item以进行测量：

\documentclass{article}
\usepackage{enumitem,environ}

\newlength{\xitemlenx}
\newlength{\xitemleny}
\NewEnviron{xitemize}{%
  \setbox0=\vbox{
    \xitemlenx=0pt
    \def\item[##1]{\measureitem{##1}}
    \BODY
    \global\xitemleny\xitemlenx
  }%
  \itemize[
    leftmargin=\dimexpr\xitemleny+\labelsep,
    labelwidth=\xitemleny,
    align=left
  ]
  \BODY
  \enditemize
}
\newcommand{\measureitem}[1]{%
  \settowidth{\dimen0}{#1}%
  \ifdim\dimen0>\xitemlenx
    \xitemlenx=\dimen0
  \fi
}

\begin{document}

Just enough text to make the line break so we get to see a second line.
Just enough text to make the line break so we get to see a second line.
\begin{xitemize}
  \item[Foo] An item
  \item[Foo Bar Foo] An item An item An item An item An item An item An item An item An item An item An item An item An item An item  
  \item[Bar Bar] An item 
\end{xitemize}
Just enough text to make the line break so we get to see a second line.
Just enough text to make the line break so we get to see a second line.
\end{document}

如果您需要单个项目，正如您从评论中看到的那样，这会更容易，因为只需要测量一个标签；这是集成在前面的代码中的想法。

\documentclass{article}
\usepackage{enumitem,environ}

\newlength{\xitemlenx}
\newlength{\xitemleny}
\NewEnviron{xitemize}{%
  \setbox0=\vbox{
    \xitemlenx=0pt
    \def\item[##1]{\measureitem{##1}}
    \BODY
    \global\xitemleny\xitemlenx
  }%
  \itemize[
    leftmargin=\dimexpr\xitemleny+\labelsep,
    labelwidth=\xitemleny,
    align=left
  ]
  \BODY
  \enditemize
}
\newcommand{\measureitem}[1]{%
  \settowidth{\dimen0}{#1}%
  \ifdim\dimen0>\xitemlenx
    \xitemlenx=\dimen0
  \fi
}

\newcommand{\singleitem}[2]{%
  \settowidth{\xitemleny}{#1}%
  \begin{itemize}[
    leftmargin=\dimexpr\xitemleny+\labelsep,
    labelwidth=\xitemleny,
    align=left
  ]
  \item[#1]\textbf{#2}
  \end{itemize}%
}

\begin{document}

Just enough text to make the line break so we get to see a second line.
Just enough text to make the line break so we get to see a second line.
\begin{xitemize}
  \item[Foo] An item
  \item[Foo Bar Foo] An item An item An item An item An item An item An item An item An item An item An item An item An item An item  
  \item[Bar Bar] An item 
\end{xitemize}
Just enough text to make the line break so we get to see a second line.
Just enough text to make the line break so we get to see a second line.
Now a single item:
\singleitem{Foo Bar}{An item An item An item An item An item An item An item An item An item An item An item An item An item An item}
Just enough text to make the line break so we get to see a second line.
Just enough text to make the line break so we get to see a second line.

\end{document}

Answer 2

使用结合了和ltablex功能的软件包，一切都变得非常容易：tabularxlongtable

\documentclass{book}
\usepackage[utf8]{inputenc}
\usepackage{fourier, heuristica}
\usepackage{array, ltablex}

\begin{document}
\noindent Just enough text to make the line break so we get to see a second line. Text text text text tex text text text tex.

\begin{tabularx}{\linewidth}{@{}l@{\quad}X@{}}
 Foo & An item \\
Foo Bar Foo & An item An item An item An item An item An item An item An item An item An item An item An item An item An item\\
Bar Bar & An item
\end{tabularx}
Just enough text to make the line break so we get to see a second line. Text text text text tex text text text tex.

\end{document}