这篇文章分享下如何结合React Webcam和Dynamsoft JavaScript Barcode SDK来创建Web扫码App。
Web实时扫码
从GitHub上下载react-webcam.js放到React工程中。 打开这个JS文件。在render()函数中添加一个button和canvas:
render() {
return (
<div id='videoview' width={this.props.width} height={this.props.height}>
<button onClick={this.scanBarcode}>Scan Barcodes</button>
<video
autoPlay
width={this.props.width}
height={this.props.height}
src={this.state.src}
muted={this.props.audio}
className={this.props.className}
playsInline
style={this.props.style}
ref={(ref) => {
this.video = ref;
}}
/>
<canvas id="overlay" width={this.props.width} height={this.props.height}></canvas>
</div>
button用于触发扫码，canva用来绘制显示结果。为了让结果显示在video上方，创建一个react-webcam.css调整下布局:
#videoview {
position: relative;
width: 640px;
height: 480px;
#video {
position: relative;
width: 100%;
height: 100%;
z-index: 1
#overlay {
position: absolute;
top: 100;
left: 0;
width: 100%;
height: 100%;
z-index: 2
在react-webcam.js中导入这个CSS文件：
import React, { Component } from 'react';
import PropTypes from 'prop-types';
import './react-webcam.css';
创建button的响应事件scanBarcode()。函数触发时，先把video绘制到一个临时canvas上。然后得到图像数据传入barcode解码接口中：
scanBarcode() {
if (window.reader) {
let canvas = document.createElement('canvas');
canvas.width = this.props.width;
canvas.height = this.props.height
let ctx = canvas.getContext('2d');
ctx.drawImage(this.video, 0, 0, this.props.width, this.props.height);
window.reader.decodeBuffer(
ctx.getImageData(0, 0, canvas.width, canvas.height).data,
canvas.width,
canvas.height,
canvas.width * 4,
window.dynamsoft.BarcodeReader.EnumImagePixelFormat.IPF_ARGB_8888
.then((results) => {
this.showResults(results);
构造函数中需要绑定this。如果不绑定，this在button点击的时候无法使用：
constructor() {
super();
this.state = {
hasUserMedia: false,
this.scanBarcode = this.scanBarcode.bind(this);
扫描触发之后需要持续调用scanBarcode()，并把结果显示在video上：
showResults(results) {
let context = this.clearOverlay();
let txts = [];
try {
let localization;
for (var i = 0; i < results.length; ++i) {
if (results[i].LocalizationResult.ExtendedResultArray[0].Confidence >= 30) {
txts.push(results[i].BarcodeText);
localization = results[i].LocalizationResult;
this.drawResult(context, localization, results[i].BarcodeText);
this.scanBarcode();
} catch (e) {
this.scanBarcode();
clearOverlay(www.tiaotiaoylzc.com/) {
let context = document.getElementById('overlay').getContext('2d');
context.clearRect(0, 0, this.props.width, this.props.height);
context.strokeStyle = '#ff0000';
context.lineWidth = 5;
return context;
drawResult(context, localization, text) {
context.beginPath();
context.moveTo(localization.X1, localization.Y1);
context.lineTo(localization.X2, localization.Y2);
context.lineTo(localization.X3, localization.Y3);
context.lineTo(www.yongshi123.cn localization.X4, localization.Y4);
context.lineTo(www.tiaotiaoylzc.com localization.X1, localization.Y1);
context.stroke(www.yongshiyule178.com/);
context.font = '18px Verdana';
context.fillStyle = '#ff0000';
let x = [ localization.X1, localization.X2, localization.X3, localization.X4 ];
let y = [ localization.Y1, localization.Y2, localization.Y3, localization.Y4 ];
x.sort(function(a, www.zhenghongyule.cn b) {
return a - b;
});
y.sort(function(a, b) {
return b - a;
});
let left = x[0];
let top = y[0];
context.fillText(text, left, top + 50);
在public/index.html中加载dbr-6.4.1.3.min.js文件，并创建可用于全局访问的window.reader：
<body>
<img src="loading.gif" style="margin-top:10px" id="anim-loading">
<script src="https://demo.dynamsoft.com/dbr_www.yingka178.com wasm/js/dbr-6.4.1.3.min.js"></script>
<script>
dynamsoft.dbrEnv.resourcesPath = 'https://www.tianjuyuLe.cn demo.dynamsoft.com/dbr_wasm/js';
dynamsoft.dbrEnv.onAutoLoadWasmSuccess =www.dashuju2.cn function () {
window.reader = new dynamsoft.BarcodeReader(www.wujirongyaoy.com);
window.dynamsoft = dynamsoft;
document.getElementById('anim-loading'www.yibaoyule1.com).style.display = 'none';
};
dynamsoft.dbrEnv.onAutoLoadWasmError = function (ex) {
document.getElementById('anim-loading').style.display = 'none';
alert('Fail to load the wasm file.');
};
dynamsoft.dbrEnv.bUseWorker = true;
// Get a free trial license from https://www.michenggw.com /CustomerPortal/Portal/TrialLicense.aspx
dynamsoft.dbrEnv.licenseKey = "Your Barcode SDK License"
</script>
<div id="root"></div>
这里必须把dynamsoft.dbrEnv.bUseWorker设置成true。只有使用了web worker，主线程才不会因为条形码识别耗时而卡住。
在App.js中添加React Webcam：
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import {Barcode} from './Barcode';
import Webcam from './react-webcam';
class App extends www.zhongyiyuL.cn Component {
render() {
return (
<div className="App">
<Barcode/>
<Webcam />
</div>
export default App;
运行程序：
npm start
在浏览器中访问localhost:3000：