边缘上文本两侧的箭头

Question

如何如图所示放置箭头？

      \documentclass[tikz]{standalone}

      \usetikzlibrary{arrows.meta, bending, quotes, shapes.geometric}

      \begin{document}
      \begin{tikzpicture}
             [-{stealth[bend]}, auto, very thick,
              node distance=3cm,
              shorten >=2pt, shorten <=2pt,
              mynode/.style={circle,draw, thick, minimum size=8mm,
              inner sep=2pt},
              every edge quotes/.style={anchor=mid,circle,fill=white,
                                 inner sep=1pt}  
             ]

            \node[mynode] (1) at (1,4) {1};
            \node[mynode] (2) at (6,5) {2};
            \node[mynode] (3) at (8,1) {3};
            \node[mynode] (4) at (10,4){4};

           \path[blue](1.east) edge["b"] (2.west)
                      (1.east) edge[bend left=30,"a"]  (2.west)
                      (2.west) edge[bend left=30,"c"] (1.east)
                      (1.east) edge[bend right=30,"b"] (3.west)
                      (3.east) edge[bend right=40,"b"] (4.south)
                      (4.north west) edge[bend right=40,"c"] (2.east)
                      (2.south east) edge[bend left=30,"b"] (3.north);
           \draw[blue] ([yshift=-2pt] 3.west) arc (-235:55:0.7)
                       node[midway,below] {a};
           \draw[blue,line width=1mm,-{Stealth[bend]}] (-1,4) -- (1.west);

           \end{tikzpicture}
           \end{document}

Answer 1

像这样？

\documentclass[tikz, margin=3mm]{standalone}
\usetikzlibrary{arrows.meta,
                bending, 
                decorations.markings,
                quotes
                }

\begin{document}
    \begin{tikzpicture}[
shorten >=2pt, shorten <=2pt, arrows={[bend]},  
->-/.style = {decoration={markings,
              mark=at position 0.25 with {\arrow{Stealth}}, 
              mark=at position 0.75 with {\arrow{Stealth}}},
              very thick, draw=blue,
              postaction={decorate}},
every edge/.style = {->-},
    mynode/.style = {circle, draw, thick, minimum size=8mm, inner sep=2pt},
every edge quotes/.style = {circle, fill=white, anchor=mid, inner sep=1pt}
                    ]
\node[mynode] (1) at (1,4) {1};
\node[mynode] (2) at (6,5) {2};
\node[mynode] (3) at (8,1) {3};
\node[mynode] (4) at (10,4){4};

\draw 
    (1) edge["b"] (2)
    (1) edge[bend left,"a"]  (2)
    (2) edge[bend left,"c"]  (1)
    (1) edge[bend right,"b"] (3)
    (3) edge[bend right=40,"b"] (4)
    (4) edge[bend right=40,"c"] (2)
    (2) edge[bend left,"b"]  (3);
\draw[->-]
    (3.195) arc (-240:60:0.8) node[midway,fill=white] {a};
\draw[blue,line width=1mm,-Stealth] (-1,4) -- (1.west);
    \end{tikzpicture}
\end{document}

编辑： 添加的箭头指向循环，就像其他箭头一样。

Answer 2

我不想用白色覆盖所有东西，而是想添加弯曲的箭头。这可以通过show path construction随附的装饰来实现。我添加了一种注重细节的decorations.pathreplacing风格。mid label

\documentclass[tikz]{standalone}

\usetikzlibrary{arrows.meta, bending, quotes,shapes.geometric,decorations.pathreplacing}

\tikzset{mid label/.style={decoration={show path construction,
moveto code={},
lineto code={
\path  (\tikzinputsegmentfirst) 
-- (\tikzinputsegmentlast) foreach \X in {4,8} {coordinate[pos=0.1*\X] (aux-\X)}
 node[midway,auto=false] (aux){#1};
\draw[-]  (\tikzinputsegmentfirst) -- (aux);
\draw[->]  (\tikzinputsegmentfirst) -- (aux-4);
\draw[-]  (\tikzinputsegmentlast) -- (aux);
\draw[->]  (aux) -- (aux-8);
},
curveto code={
\path  (\tikzinputsegmentfirst) .. controls
(\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb)
..(\tikzinputsegmentlast)  
foreach \X in {0,...,10} {coordinate[pos=0.1*\X] (aux-\X)}
node[midway,auto=false] (aux){#1};
\draw[-] plot[smooth,samples at={0,...,4}] (aux-\x) -- (aux);
\draw[->] plot[smooth,samples at={0,1,2,3}] (aux-\x);
\draw[-]  plot[smooth,samples at={10,9,8,7,6}] (aux-\x) -- (aux);
\draw[<-]  plot[smooth,samples at={8,7,6}] (aux-\x) -- (aux);
},
closepath code={
}
},decorate}}

\begin{document}
\begin{tikzpicture}
       [>={Stealth[bend]}, auto, very thick,
        node distance=3cm,
        shorten >=2pt, shorten <=2pt,
        mynode/.style={circle,draw, thick, minimum size=8mm,
        inner sep=2pt},
        every edge quo tes/.style={anchor=mid,circle,fill=white,
                           inner sep=1pt}  
       ]

      \node[mynode] (1) at (1,4) {1};
      \node[mynode] (2) at (6,5) {2};
      \node[mynode] (3) at (8,1) {3};
      \node[mynode] (4) at (10,4){4};
     \path ([yshift=-1cm]3.south) node (a){a};

     \path[blue](1.east) edge[mid label=b] (2.west)
                (1.east) edge[bend left=30,mid label=a]  (2.west)
                (2.west) edge[bend left=30,mid label=c] (1.east)
                (1.east) edge[bend right=30,mid label=b] (3.west)
                (3.east) edge[bend right=40,mid label=b] (4.south)
                (4.north west) edge[bend right=40,mid label=c] (2.east)
                (2.south east) edge[bend left=30,mid label=b] (3.north);                
     \draw[blue,->,shorten >=0,shorten <=0] (3) to[out=-150,in=180,looseness=1.5]  (a);
     \draw[blue,<-,shorten >=0,shorten <=0] (3) to[out=-30,in=0,looseness=1.5]  (a);
     \draw[blue,line width=1mm,->] (-1,4) -- (1.west);

\end{tikzpicture}
\end{document}