TikZ：如何仅对存在的坐标使用绘制选项/foreach 问题

Question

我有一些坐标（比如 A、B、C）。

现在我做了这样的事情：\foreach \P in {A,B,C} \draw[fill=pink] (\P) circle[radius=2.5pt];

如果我说\foreach \P in {A,B,C,X} \draw[fill=pink] (\P) circle[radius=2.5pt];

我会得到错误No shape named 'X' is known.

所以我的问题是：我怎么能有像符号代码这样的东西

\ifcoordinateexist 
\draw[fill=pink]  (\P) circle[radius=2.5pt];
\else % nothing
\fi

我有一个简单的解决方案，也许使用 TikZ-tools？

\documentclass[border=2mm, tikz]{standalone}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}[]
\coordinate[label=A](A) at (0,0);
\coordinate[label=B](B) at (2,3);
\coordinate[label=C](C) at (1,1);

% Will work:
\foreach \P in {A,B,C} \draw[fill=pink]  (\P) circle[radius=2.5pt]; 


%% Will not work:
%\foreach \P in {A,B,C,X} \draw[fill=pink]  (\P) circle[radius=2.5pt]; 
% ---------> No shape named `X' is known.
\end{tikzpicture}
\end{document}

Answer 1

正如指出我之前的评论，

tikz 节点是全局定义的（也在Martin Scharrer 的原始答案），因此如果X在先前的 tikzpicture 中定义了一个节点，那么这个测试\ifcoorddefined（这个答案) 将会失败。

这是一个增强的测试器，可以测试给定的节点是否在当前（由 内部使用的环境）\ifNodeDefined{<node name>}{<true>}{<false>}中定义。pgfpicuretikzpicture

\documentclass{article}
\usepackage{tikz}

\makeatletter
\long\def\ifcoorddefined#1#2#3{%
    \@ifundefined{pgf@sh@ns@#1}{#3}{#2}%
}

\def\ifNodeDefined#1{%
    \@ifundefined{pgf@sh@ns@#1}{\@secondoftwo}{%
      \expandafter\ifx\csname pgf@sh@pi@#1\endcsname\pgfpictureid
        \expandafter\@firstoftwo
      \else
        \expandafter\@secondoftwo
      \fi}%
}
\makeatother

\begin{document}

\begin{tikzpicture}
  \coordinate[label=X] (X) at (1,0);
  \coordinate[label=Y] (Y) at (0,1);
\end{tikzpicture}
\qquad
\begin{tikzpicture}[baseline=0pt]
  \coordinate[label=A] (A) at (0,0);
  \coordinate[label=B] (B) at (2,3);
  \coordinate[label=C] (C) at (1,1);
  
  \foreach \P in {A,B,C, X, Y, L, M}{
    \ifcoorddefined{\P}
      {\draw[fill=pink] (\P) circle[radius=2pt];}
      {}
  }
  \node[anchor=north] at (1,-.5) {old tester};
\end{tikzpicture}
\qquad
\begin{tikzpicture}[baseline=0pt]
  \coordinate[label=A] (A) at (0,0);
  \coordinate[label=B] (B) at (2,3);
  \coordinate[label=C] (C) at (1,1);
  
  \foreach \P in {A,B,C, X, Y, L, M}{
    \ifNodeDefined{\P}
      {\draw[fill=pink] (\P) circle[radius=2pt];}
      {}
  }
  \node[anchor=north] at (1,-.5) {new tester};
\end{tikzpicture}

\end{document}

Answer 2

我在这里找到了一个解决方案： https://tex.stackexchange.com/a/85531/46023

\documentclass[border=2mm, tikz]{standalone}
\usepackage{tikz}
\begin{document}

\makeatletter
\long\def\ifcoorddefined#1#2#3{%
    \@ifundefined{pgf@sh@ns@#1}{#3}{#2}%
}
\makeatother

\begin{tikzpicture}[]
\coordinate[label=A](A) at (0,0);
\coordinate[label=B](B) at (2,3);
\coordinate[label=C](C) at (1,1);

\foreach \P in {A,B,C, X, Y, L, M}{
  \ifcoorddefined{\P}{  \draw[fill=pink] (\P) circle[radius=2pt];  }{}
}
\end{tikzpicture}

\end{document}