TikZ：如果使用小字体，节点文本会分成多行，间距太大

Question 1

不要将字体大小命令与节点文本一起使用！它应由节点参数决定：

\documentclass[12pt,letterpaper]{article}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}

\begin{document}

\tikzstyle{block} = [draw, rectangle,
minimum height=3em, minimum width=5em, align=left]
\tikzstyle{pinstyle} = [pin edge={to-,thin,black}]

% The block diagram code is probably more verbose than necessary
\begin{tikzpicture}[auto,>=latex']
% We start by placing the blocks
    \node [block, name=message-source] {message \\ source};
    \node [block, name=encoder, right of=message-source, node distance=3.5cm] {encoder};
    \node [block, name=channel, right of=encoder, node distance=3.5cm, pin={[pinstyle]above:\scriptsize noise},
    node distance=3.5cm] {channel};
    \node [block, name=decoder, right of=channel, node distance=3.5cm] {decoder};
    \node [block, name=user, right of=decoder, node distance=3.5cm] {user};

    % Once the nodes are placed, connecting them is easy.
    \draw [->] (message-source) -- node[name=message, align=center] {\scriptsize message} (encoder);
    \draw [->] (encoder) -- node[name=codeword, align=center] {\scriptsize codeword} (channel);
    \draw [->] (channel) -- node[name=receivedword, align=center, text width=1.75cm,
                                 font=\scriptsize] { received word} (decoder);  <-- here is correct definition of font size!
    \draw [->] (decoder) -- node[name=decodedmsg, align=center, text width=1.75cm] {{\scriptsize decoded message}} (user);
\end{tikzpicture}

\end{document}

我只在一个节点上改变这一点，你会看到差异：

升级：您的 MWE 的另一种编码（仅供我练习，但也许您会喜欢它）：

\documentclass[12pt,letterpaper]{article} \usepackage{tikz} \usetikzlibrary{箭头,链条,引号}

\usepackage[margin=0.75in,showframe]{几何}

    \begin{document}
\noindent%
    \begin{tikzpicture}[
    node distance = 7mm and 18mm,
      start chain = going right,
     block/.style = {rectangle, draw, 
                     minimum height=3em, minimum width=5em, align=left,
                     on chain},
every edge/.style = {draw,-latex'},
every edge quotes/.style = {auto, text width=17mm, align=center, font=\scriptsize},
 every pin/.style = {in distance=7mm, font=\scriptsize},
   every pin edge/.style = {black, latex'-},
                        ]
% We start by placing the blocks
\node [block, name=message-source]  {message\\ source};
\node [block, name=encoder]         {encoder};
\node [block, name=channel,
       pin=above:noise]             {channel};
\node [block, name=decoder]         {decoder};
\node [block, name=user]            {user};

% Once the nodes are placed, connecting them is easy.
\draw   (message-source) edge["message"] (encoder)
        (encoder) edge["codeword"] (channel) 
        (channel) edge["received word"] (decoder)
        (decoder) edge["decoded message"] (user);
\end{tikzpicture}
    \end{document}

这个更简洁的代码给出了与以前相同的结果。在其中我使用 tikzlibraryquotes来标记块之间的箭头。所有样式的定义都集中在图片代码的开头（可以放在中\tikzset，\tikzstyle已弃用）。借助链库，节点位于“链”中，它们之间的距离由决定node distance。

Answer