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class="container" id="main-content" tabindex="-1"><div class="post"><article class="post-block h-entry"><div class="post-meta p-author h-card visually-hidden"><img class="author-avatar u-photo" src="../favicon.png" alt="Cytrogen"><span class="p-name">Cytrogen</span><a class="u-url" href="https://cytrogen.icu">https://cytrogen.icu</a></div><a class="post-permalink u-url u-uid visually-hidden" href="https://cytrogen.icu/posts/14d5.html">永久链接</a><div class="p-summary visually-hidden"><p>上次提到过我接触了一个新项目，是校友们策划的一个类 ChatGPT 的项目，我负责前端部分，用的是 React + TailwindCSS 的组合。 我这个刚接触 React 一个月的小白肯定是搓手等着上手、跃跃欲试。</p>
<p>像是 ChatGPT、Claude，甚至是 Discord 这样的聊天室 App，输入框都是能够让用户换行、输入代码块的。我们的项目也不例外。 但是，<code>textarea</code> 组件就算是默认单行，换行时也会向下增加高度，导致脱离原本的父容器，甚至跑到屏幕外面去。</p></div><div class="visually-hidden"><a class="p-category" href="../categories/%E7%BC%96%E7%A8%8B%E7%AC%94%E8%AE%B0/">编程笔记</a><a class="p-category" href="../tags/JavaScript/">JavaScript</a><a class="p-category" href="../tags/React-js/">React.js</a></div><h1 class="post-title p-name">React 的 Textarea 高度自适应</h1><div class="post-info"><time class="post-date dt-published" datetime="2024-02-20T04:11:13.000Z">2/19/2024</time><time class="dt-updated visually-hidden" datetime="2026-02-09T17:16:55.001Z"></time></div><div class="post-content e-content"><html><head></head><body><p>上次提到过我接触了一个新项目，是校友们策划的一个类 ChatGPT 的项目，我负责前端部分，用的是 React + TailwindCSS 的组合。 我这个刚接触 React 一个月的小白肯定是搓手等着上手、跃跃欲试。</p>
<p>像是 ChatGPT、Claude，甚至是 Discord 这样的聊天室 App，输入框都是能够让用户换行、输入代码块的。我们的项目也不例外。 但是，<code>textarea</code> 组件就算是默认单行，换行时也会向下增加高度，导致脱离原本的父容器，甚至跑到屏幕外面去。</p>
<span id="more"></span>
<h2 id="最终结果"><a class="markdownIt-Anchor" href="#最终结果"></a> 最终结果</h2>
<p><img src="/posts/14d5/result.png" alt="result"></p>
<h2 id="环境"><a class="markdownIt-Anchor" href="#环境"></a> 环境</h2>
<p>先说父容器的样式，一个带了 <code>flex</code> 的 <code>div</code>：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><div className=<span class="string">"flex flex-col h-full"</span>></span><br><span class="line"> <span class="language-xml"><span class="tag"><<span class="name">div</span> <span class="attr">className</span>=<span class="string">"flex-1"</span>></span>{/* 信息内容 */}<span class="tag"></<span class="name">div</span>></span></span></span><br><span class="line"> </span><br><span class="line"> {<span class="comment">/* 主角 */</span>}</span><br><span class="line"> <<span class="title class_">Textbox</span> /></span><br><span class="line"></div></span><br></pre></td></tr></tbody></table></figure>
<p>而 <code>Textbox</code> 组件的样式差不多是这样的：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><div className=<span class="string">"flex items-center w-full"</span>></span><br><span class="line"> <span class="language-xml"><span class="tag"><<span class="name">textarea</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">name</span>=<span class="string">"message"</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">className</span>=<span class="string">"w-full resize-none"</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">placeholder</span>=<span class="string">"Type a message..."</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">rows</span>=<span class="string">"1"</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> /></span></span></span><br><span class="line"> <span class="language-xml"><span class="tag"><<span class="name">button</span>></span>发送<span class="tag"></<span class="name">button</span>></span></span></span><br><span class="line"></div></span><br></pre></td></tr></tbody></table></figure>
<p>正常来说，<code>textarea</code> 的大小是朝下无限增长的，但这不是我们想要的，我们希望它能够朝上增长、挤压信息内容的高度，直到达到一定高度后出现滚动条。</p>
<h2 id="解决方案"><a class="markdownIt-Anchor" href="#解决方案"></a> 解决方案</h2>
<p>为什么要特意说到父容器是一个带了 <code>flex</code> 的 <code>div</code> 呢？因为这是解决问题的关键。</p>
<p>包含了信息内容的兄弟元素会铺满剩余没有被 <code>Textbox</code> 组件占用的空间，而 <code>Textbox</code> 组件的高度是可以动态修改的。</p>
<p>也就是说，我们可以通过监听 <code>textarea</code> 的 <code>scrollHeight</code> 属性，来动态修改 <code>Textbox</code> 整个组件的高度，最终保持让它一直待在父容器的里面。</p>
<p>先创建一个 <code>useRef</code> 来引用 <code>textarea</code>：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">const</span> textareaRef = <span class="title function_">useRef</span>(<span class="literal">null</span>);</span><br><span class="line"></span><br><span class="line"><span class="comment">// ... </span></span><br><span class="line"></span><br><span class="line"><span class="language-xml"><span class="tag"><<span class="name">textarea</span> <span class="attr">ref</span>=<span class="string">{textareaRef}</span> /></span></span></span><br></pre></td></tr></tbody></table></figure>
<p>我们还需要创建一个 <code>useState</code> 来保存我们想要的高度：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">const</span> [height, setHeight] = <span class="title function_">useState</span>(<span class="number">40</span>);</span><br></pre></td></tr></tbody></table></figure>
<blockquote>
<p>这里的 <code>40</code> （像素）是我自己设定的一个最小高度。</p>
</blockquote>
<p>创建 <code>useEffect</code> 来监听 <code>textarea</code> 的 <code>scrollHeight</code> 属性：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="title function_">useEffect</span>(<span class="function">() =></span> {</span><br><span class="line"> <span class="keyword">const</span> <span class="title function_">handleResize</span> = (<span class="params"></span>) => {</span><br><span class="line"> <span class="keyword">const</span> textareaElement = textareaRef.<span class="property">current</span>;</span><br><span class="line"> textareaElement.<span class="property">style</span>.<span class="property">height</span> = <span class="string">"auto"</span>;</span><br><span class="line"> textareaElement.<span class="property">style</span>.<span class="property">height</span> = <span class="string">`<span class="subst">${textareaElement.scrollHeight}</span>px`</span>;</span><br><span class="line"> <span class="title function_">setHeight</span>(<span class="title class_">Math</span>.<span class="title function_">max</span>(<span class="number">40</span>, textareaElement.<span class="property">scrollHeight</span>));</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">const</span> textareaElement = textareaRef.<span class="property">current</span>;</span><br><span class="line"> textareaElement.<span class="title function_">addEventListener</span>(<span class="string">"input"</span>, handleResize);</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> <span class="function">() =></span> textareaElement.<span class="title function_">removeEventListener</span>(<span class="string">"input"</span>, handleResize);</span><br><span class="line">}, []);</span><br></pre></td></tr></tbody></table></figure>
<p>在 <code>handleResize</code> 中，我们先将 <code>textarea</code> 的高度设置为 <code>auto</code>，这样就可以让它自己决定高度，然后用 <code>setHeight</code> 来保存 <code>scrollHeight</code> 的值。</p>
<blockquote>
<p><code>Math.max(40, textareaElement.scrollHeight)</code> 是为了保证 <code>textarea</code> 的高度不会小于 <code>40</code> 像素，也就是我刚才说的，我自己设定的一个最小高度。</p>
</blockquote>
<p><code>handleResize</code> 需要在用户输入时触发，所以还要用 <code>addEventListener</code> 来监听 <code>input</code> 事件。</p>
<p>最后别忘了卸载监听器。</p>
<p>那么我们得到的 <code>height</code> 要用在哪里呢？<code>Textbox</code> 组件的最外层 <code>div</code> 上：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><div className=<span class="string">"flex items-center w-full"</span> style={{ <span class="attr">height</span>: <span class="string">`<span class="subst">${height}</span>px`</span> }}></span><br><span class="line"> <span class="language-xml"><span class="tag"><<span class="name">textarea</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">name</span>=<span class="string">"message"</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">className</span>=<span class="string">"w-full resize-none"</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">placeholder</span>=<span class="string">"Type a message..."</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">rows</span>=<span class="string">"1"</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> <span class="attr">ref</span>=<span class="string">{textareaRef}</span></span></span></span><br><span class="line"><span class="tag"><span class="language-xml"> /></span></span></span><br><span class="line"> <span class="language-xml"><span class="tag"><<span class="name">button</span>></span>发送<span class="tag"></<span class="name">button</span>></span></span></span><br><span class="line"></div></span><br></pre></td></tr></tbody></table></figure>
<p>每次用户输入，<code>height</code> 都会被更新，<code>Textbox</code> 组件的高度也会被更新。拥有着固定高度的 <code>Textbox</code> 组件能够在 Flexbox 布局中自由伸缩，装有信息内容的兄弟元素则会根据 <code>Textbox</code> 组件的高度自动调整。</p>
<p>不过呢还是有需求没能完成：<code>Textbox</code> 组件要在伸展到一定高度时出现滚动条。之后再说吧。</p>
<h2 id="后话"><a class="markdownIt-Anchor" href="#后话"></a> 后话</h2>
<p>其实之后测试时发现还是有问题的，原因很简单：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">onKeyDown={<span class="function"><span class="params">e</span> =></span> {</span><br><span class="line"> <span class="keyword">if</span> (e.<span class="property">key</span> === <span class="string">"Enter"</span> && !e.<span class="property">shiftKey</span>) {</span><br><span class="line"> e.<span class="title function_">preventDefault</span>(); <span class="comment">// 我当时忘记加这一句了</span></span><br><span class="line"> <span class="title function_">handleSendMessage</span>(e.<span class="property">target</span>.<span class="property">value</span>)</span><br><span class="line"> .<span class="title function_">then</span>(<span class="function"><span class="params">r</span> =></span> <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">"Message sent"</span>))</span><br><span class="line"> .<span class="title function_">catch</span>(<span class="function"><span class="params">e</span> =></span> <span class="variable language_">console</span>.<span class="title function_">error</span>(<span class="string">"Error in sending message:"</span>, e));</span><br><span class="line"> }</span><br><span class="line">}}</span><br></pre></td></tr></tbody></table></figure>
<p>因为没有添加 <code>e.preventDefault()</code> 导致每次发送消息时都会多出一行，<code>scrollHeight</code> 也会多出一行，最终导致 <code>Textbox</code> 组件的高度一直在增加、甚至超出父容器。</p>
<p>切记不要忘了啊！血的教训！让我白白修了一天的 bug！</p>
<p><code>handleSize</code> 也可以更新为：</p>
<figure class="highlight jsx"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">const</span> <span class="title function_">handleResize</span> = e => {</span><br><span class="line"> e.<span class="property">target</span>.<span class="property">style</span>.<span class="property">height</span> = <span class="string">`inherit`</span>;</span><br><span class="line"> e.<span class="property">target</span>.<span class="property">style</span>.<span class="property">height</span> = <span class="string">`<span class="subst">${e.target.scrollHeight}</span>px`</span>;</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">if</span> (e.<span class="property">target</span>.<span class="property">scrollHeight</span> > <span class="number">232</span>) {</span><br><span class="line"> e.<span class="property">target</span>.<span class="property">style</span>.<span class="property">overflowY</span> = <span class="string">"scroll"</span>;</span><br><span class="line"> e.<span class="property">target</span>.<span class="property">style</span>.<span class="property">height</span> = <span class="string">"232px"</span>;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> e.<span class="property">target</span>.<span class="property">style</span>.<span class="property">overflowY</span> = <span class="string">"hidden"</span>;</span><br><span class="line"> e.<span class="property">target</span>.<span class="property">style</span>.<span class="property">height</span> = <span class="title class_">Math</span>.<span class="title function_">max</span>(<span class="number">40</span>, e.<span class="property">target</span>.<span class="property">scrollHeight</span>);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>这样当 <code>scrollHeight</code> 超过 <code>232</code> 时（在我的案例中也就是 9 行），就会停止增加高度、出现滚动条。</p>
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