检测空的 PGFKEYS

Question 1

我发现您的代码的主要问题是行\ifx\getValue{@mLT/Label}\empty。的行为\ifx是比较紧随其后的两个标记\ifx并检查它们是否相同。在这种情况下，这两个标记是\getValue和{。这两个标记永远不会相同，因此始终会采用错误分支。

解决方法是将\pgfkeysgetvalue值存储到宏中，然后进行比较：

\newcommand{\leftTailA}[1]{%
  \declare{@mLT/}%
  \setValue{@mLT, Label = #1 }%
  \pgfkeysgetvalue{@mLT/Label}{\temp}
  \ifx\getValue\temp\empty
  \else
    $>$\getValue{@mLT/Label}$<$%
  \fi
}

同样，中的比较\leftTailB也是错误的。一种解决方法是将的参数存储\leftTailB到宏中，然后将该宏与进行比较，\empty如下\ifx所示：

\newcommand{\leftTailB}[1]{%
  \def\temp{#1}%
  \ifx\temp\empty
  \else
    $>$#1$<$%
  \fi
}

如果要进行多次比较，可以定义一个名为的命令\ifempty：

\makeatletter
\def\ifempty#1{%
    \def\temp{#1}%
    \ifx\temp\empty
       \expandafter\@firstoftwo
    \else
       \expandafter\@secondoftwo
    \fi
}

\def\ifpgfkeyempty#1{%
    \pgfkeysgetvalue{#1}{\temp}%
    \ifx\temp\empty
       \expandafter\@firstoftwo
    \else
       \ifx\temp\relax
           \expandafter\expandafter\expandafter\@firstoftwo
       \else
           \expandafter\expandafter\expandafter\@secondoftwo
       \fi
    \fi
}
\makeatother

in是未定义键的参数。您定义一个未定义键处理程序，它将任何未定义的键变成一个新键并存储传递给它##1的\declare值。如果您直接说：

/variables/.unknown/.style = {\pgfkeyscurrentpath/\pgfkeyscurrentname/.initial = #1}

然后\pgfkeys{/variables/some new key=some value}将其some new key变成一个新变量 key 并存储some value到其中。在宏内部，#1指的是宏的第一个参数。 doubled##用于转义#1，以便它指的是未定义 key 的参数，而不是的参数\declare。

#1为了表明和之间的关系##1，请考虑以下代码：

 \def\test#1{\def\testinner##1{(#1/##1)}}
 \test{a} % This defines \testinner as #1->(a/#1)
 \testinner{b} % expands to (a/b)

完整代码（顺便说一下，这仍然不是好的代码）：

\documentclass{minimal}
\usepackage{etoolbox}
\usepackage{pgfkeys}

\newcommand{\setValue}[1]{\pgfkeys{/variables/#1}}
\newcommand{\getValue}[1]{\pgfkeysvalueof{/variables/#1}}
\newcommand{\declare}[1]{%
 \pgfkeys{
  /variables/#1.is family,
  /variables/#1.unknown/.style = {\pgfkeyscurrentpath/\pgfkeyscurrentname/.initial = ##1}
 }%
}

\declare{}

\makeatletter
\def\ifempty#1{%
    \def\temp{#1}%
    \ifx\temp\empty
       \expandafter\@firstoftwo
    \else
       \expandafter\@secondoftwo
    \fi
}

\def\ifpgfkeyempty#1{%
    \pgfkeysgetvalue{#1}{\temp}%
    \ifx\temp\empty
       \expandafter\@firstoftwo
    \else
       \expandafter\@secondoftwo
    \fi
}
\makeatother

\newcommand{\leftTailA}[1]{%
  \declare{@mLT/}%
  \setValue{@mLT/Label = #1 }%
  \ifpgfkeyempty{/variables/@mLT/Label}{}{%
      $>$\getValue{@mLT/Label}$<$%
  }
}

\newcommand{\leftTailB}[1]{%
  \ifempty{#1}{}{%
    $>$#1$<$%
  }
}

\pgfkeys{
  /distMarkup/.is family, /distMarkup,
  default/.style = { leftTailLabel = {} },
  leftTailLabel/.estore in = \myLeftTailLabel,
}

\newcommand\distMarkup[1][]{%
  \pgfkeys{/distMarkup, default,#1}%
  \ifx\myLeftTailLabel\empty
  \else
    $>$\myLeftTailLabel$<$%
  \fi
}

\begin{document}

A: This has a label: \leftTailA{ label number 1 }

A: This has no label: \leftTailA{}

B: This has a label: \leftTailB{ label number 1 }

B: This has no label: \leftTailB{}

MA: This has a label: \distMarkup[leftTailLabel=label number 1]

MA: This has no label: \distMarkup[]

\end{document}

Answer