TikZ：带有边缘节点的箭头不正确

Question

为什么左箭头是错误的，我该如何修复它？

\documentclass[border=5pt]{standalone}

\usepackage{tikz}

\begin{document}
    \begin{tikzpicture}[auto]
    \draw[<->] (0,0) edge node {$a$} (1,0);
    \end{tikzpicture}
\end{document}  

如果没有边缘节点，它可以正常工作：

...
\draw[<->] (0,0) -- (1,0);
...

Answer 1

以下是解决此问题的几种方法。问题是edge创建了一条独立路径。正如最初指出的那样保罗·加博利，可以使用键tip=proper或tips=on proper draw，它们在 pgfmanual v3.1.4b 第 188 页中有描述。在我看来，更干净的解决方案是将箭头传递给edge。可以说最干净的方法是用 替换edge，to这样可以避免绘制两条单独的路径。还有其他选项，例如使用\path而不是绘制，但在我看来，这违背了目的，因为路径仍然存在，并且可能（至少在原则上）改变边界框，比如说。

\documentclass[border=5pt]{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[auto,font=\sffamily]
 \begin{scope}[local bounding box=original]
    \draw[<->] (0,0) edge node {$a$} (1,0); 
 \end{scope}    
 \node[above] at (original.north) {original situation};
 %
 \begin{scope}[xshift=4cm,local bounding box=proper,tips=proper]
    \draw[<->] (0,0) edge node {$a$} (1,0); 
 \end{scope}    
 \node[above] at (proper.north) {\texttt{tips=proper}};
 %
 \begin{scope}[yshift=-2cm,local bounding box=on proper draw,tips=on proper draw]
    \draw[<->] (0,0) edge node {$a$} (1,0); 
 \end{scope}    
 \node[above] at (on proper draw.north) {\texttt{tips=on proper draw}};
 %
 \begin{scope}[yshift=-2cm,xshift=4cm,local bounding box=clean]
    \draw (0,0) edge[<->] node {$a$} (1,0); 
 \end{scope}    
 \node[above] at (clean.north) {cleaner(?) solution};
 %
 \begin{scope}[yshift=-4cm,local bounding box=to]
    \draw[<->] (0,0) to node {$a$} (1,0); 
 \end{scope}    
 \node[above] at (to.north) {\texttt{to} instead of \texttt{edge}};
 %
 \begin{scope}[yshift=-4cm,xshift=4cm,local bounding box=path]
    \path[<->] (0,0) edge node {$a$} (1,0); 
 \end{scope}    
 \node[above] at (path.north) {\texttt{\textbackslash path} instead of
 \texttt{\textbackslash draw}};
\end{tikzpicture}
\end{document}  

Answer 2

一种方法是定义边：

\documentclass[border=5pt]{standalone}
\usepackage{tikz}

\begin{document}
    \begin{tikzpicture}[auto,
every edge/.style={draw, <->}
                ]
    \draw (0,0) edge node {$a$} (1,0);
    \end{tikzpicture}
\end{document}  

这使：

或者使用quotes库：

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{quotes}

\begin{document}
    \begin{tikzpicture}[auto,
every edge/.style={draw, <->}
                ]
    \draw (0,0) edge[<->, "$a$"] (1,0);
    \end{tikzpicture}
\end{document}  

或两种建议的结合。