<p>我有一个显示PDF的React组件。当我使用这个组件时，我只需要传递PDF的URL。</p>
<pre class="brush:php;toolbar:false;"><Previewer pdfUrl={pdfUrl}></Previewer></pre>
<p>组件处理预览的细节。我遇到的问题是这个组件不显示PDF。我是否遗漏了什么？我应该怎么做来解决这个问题？下面是一个演示：</p>
<p><br /></p>
<pre class="snippet-code-js lang-js prettyprint-override"><code>const { StrictMode, useRef } = React;
const { createRoot } = ReactDOM;
const styles = {};
const Previewer = (props) => {
const canvasRef = useRef(null);
React.useEffect(() => {
if (props.pdfUrl) {
initPdf(props.pdfUrl);
}
}, []);
// Converted async/await function to use promise because Stack Snippet's Babel version does not support async/await
const initPdf = (pdfUrl) => {
// Reference CDN version of PDF.js instead of using ES6 import
const pdfJS = pdfjsLib;
pdfJS.GlobalWorkerOptions.workerSrc = "https://unpkg.com/pdfjs-dist@3.9.179/build/pdf.worker.js";
return pdfJS.getDocument({
url: pdfUrl,
cMapUrl: 'https://cdn.jsdelivr.net/npm/pdfjs-dist@3.9.179/cmaps/',
cMapPacked: true,
}).promise.then((pdf) => {
const totalPages = pdf.numPages;
for (let i = 0; i < totalPages; i++) {
renderPdfPage(pdf, pdfJS, i + 1);
}
});
}
// Converted async/await function to use promise because Stack Snippet's Babel version does not support async/await
const renderPdfPage = (pdf, pdfJS, pageNum) => {
return pdf.getPage(pageNum).then((page) => {
const viewport = page.getViewport({
scale: 1.0
});
let divPage = window.document.createElement("div");
if(!canvasRef || !canvasRef.current) return;
let canvas = divPage.appendChild(window.document.createElement("canvas"));
const canvasContext = canvas.getContext('2d');
canvas.height = viewport.height;
canvas.width = viewport.width;
const renderContext = { canvasContext, viewport };
const renderTask = page.render(renderContext);
renderTask.promise.then(function () {
const textContent = page.getTextContent();
return textContent;
}).then(function (textContent) {
const textLayer = document.querySelector(`.${styles.textLayer}`);
if (!textLayer) return;
textLayer.style.left = canvas.offsetLeft + 'px';
textLayer.style.top = canvas.offsetTop + 'px';
textLayer.style.height = canvas.offsetHeight + 'px';
textLayer.style.width = canvas.offsetWidth + 'px';
textLayer.style.setProperty('--scale-factor', '1.0');
pdfJS.renderTextLayer({
textContentSource: textContent,
container: textLayer,
viewport: viewport,
textDivs: []
});
});
canvasRef.current.appendChild(divPage);
});
}
return (
<div className={styles.cavasLayer}>
<canvas id="the-cavas" ref={canvasRef} />
{/**<div className={styles.textLayer}></div>**/}
</div>
);
}
const pdfUrl = "https://mozilla.github.io/pdf.js/web/compressed.tracemonkey-pldi-09.pdf"
const root = createRoot(document.getElementById("root"));
root.render(<StrictMode><Previewer pdfUrl={pdfUrl} /></StrictMode>);</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code><script crossorigin src="https://unpkg.com/react@18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>
<script crossorigin src="https://unpkg.com/pdfjs-dist@3.9.179/build/pdf.js"></script>
<div id="root"></div></code></pre>
<p><br /></p>
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问题
在
renderPdfPage函数中，您创建了一个包含渲染PDF页面的canvas元素的div元素。然后将这些div元素附加到一个canvas元素上。然而，如果浏览器支持canvas元素，则不会渲染canvas元素的后代元素。根据canvas元素的规范：回退内容的定义如下：
解决方案
您需要将父级
canvas更改为适当的元素。在下面的演示中，我使用了一个div：const { StrictMode, useRef } = React; const { createRoot } = ReactDOM; const styles = {}; const Previewer = (props) => { const pdfContainerRef = useRef(null); React.useEffect(() => { if (props.pdfUrl) { initPdf(props.pdfUrl); } }, []); // Converted async/await function to use promise because Stack Snippet's Babel version does not support async/await const initPdf = (pdfUrl) => { // Reference CDN version of PDF.js instead of using ES6 import const pdfJS = pdfjsLib; pdfJS.GlobalWorkerOptions.workerSrc = "https://unpkg.com/pdfjs-dist@3.9.179/build/pdf.worker.js"; return pdfJS.getDocument({ url: pdfUrl, cMapUrl: 'https://cdn.jsdelivr.net/npm/pdfjs-dist@3.9.179/cmaps/', cMapPacked: true, }).promise.then((pdf) => { const totalPages = pdf.numPages; for (let i = 0; i < totalPages; i++) { renderPdfPage(pdf, pdfJS, i + 1); } }); } // Converted async/await function to use promise because Stack Snippet's Babel version does not support async/await const renderPdfPage = (pdf, pdfJS, pageNum) => { return pdf.getPage(pageNum).then((page) => { const viewport = page.getViewport({ scale: 1.0 }); let divPage = window.document.createElement("div"); if(!pdfContainerRef || !pdfContainerRef.current) return; let canvas = divPage.appendChild(window.document.createElement("canvas")); const canvasContext = canvas.getContext('2d'); canvas.height = viewport.height; canvas.width = viewport.width; const renderContext = { canvasContext, viewport }; const renderTask = page.render(renderContext); renderTask.promise.then(function () { const textContent = page.getTextContent(); return textContent; }).then(function (textContent) { const textLayer = document.querySelector(`.${styles.textLayer}`); if (!textLayer) return; textLayer.style.left = canvas.offsetLeft + 'px'; textLayer.style.top = canvas.offsetTop + 'px'; textLayer.style.height = canvas.offsetHeight + 'px'; textLayer.style.width = canvas.offsetWidth + 'px'; textLayer.style.setProperty('--scale-factor', '1.0'); pdfJS.renderTextLayer({ textContentSource: textContent, container: textLayer, viewport: viewport, textDivs: [] }); }); pdfContainerRef.current.appendChild(divPage); }); } return ( <div className={styles.cavasLayer}> <div id="pdf-container" ref={pdfContainerRef} /> {/**<div className={styles.textLayer}></div>**/} </div> ); } const pdfUrl = "https://mozilla.github.io/pdf.js/web/compressed.tracemonkey-pldi-09.pdf" const root = createRoot(document.getElementById("root")); root.render(<StrictMode><Previewer pdfUrl={pdfUrl} /></StrictMode>);