前端实现生成图片并批量下载，下载成果物是zip包

news2024/11/17 12:50:31

简介

项目上有个需求，需要根据表单填写一些信息，来生成定制的二维码图片，并且支持批量下载二维码图片。
之前的实现方式是直接后端生成二维码图片，点击下载时后端直接返回一个zip包即可。但是项目经理说后端实现方式每次改个东西都要改大半天，所以让前端来实现。

方案

1.后端返回二维码的base64url数据流，就是下图红框中的二维码图片。

在这里插入图片描述
2.前端负责展示成交互上的二维码图片样式，如下图。

在这里插入图片描述
3.点击批量下载时，用户自己选择下载数量，然后后端返回二维码base64url的数组，前端自己实现下载，且是以zip的形式下载。下载的每张图片都是前端页面上所展示的样子。

思路

比如批量下载50个，首先10个一组处理，每个二维码编号生成一个blob流，塞入生成的zip中，50个二维码编号全部处理完成后，开始下载zip，将zip转为blob流，触发下载等待下载完成。

耗时较久的是每个二维码编号生成一个blob流，需要前端拿到后端返回的二维码base64 url, 通过js代码组装成最终的图片样式的DOM，然后需要塞到页面中，再使用dom-to-image 转成图片形式的blob流。

实现

1.比如选择下载数量是50张，点击下载,触发handleDownload 函数
2.使用jszip 生成一个zip
3.print_set_root 是该页面组件中最外层的div元素
4.分10个一组进行处理

完整代码如下：

import JSZip from 'jszip'
import { chunk } from 'lodash'
import domtoimage from 'dom-to-image'

async handleDownload (val) {
  this.downBtnLoading = true
  try {
    const { data } = await downQuas({ count: Number(val), randomNum: 6, start: this.ruleForm.code })
    this.zip = new JSZip()
    const rod = document.getElementById('print_set_root')
    const arr = chunk(data, 10)
    for (let i = 0; i < arr.length; i++) {
      await this.usePromiseArr(arr[i], rod)
    }
    this.downBtnLoading = false
    const that = this
    this.zip.generateAsync({ type: 'blob' }).then(function (base64) {
      const url = URL.createObjectURL(base64)
      const link = document.createElement('a')
      link.download = `${that.regionName}.zip`
      link.href = url
      link.click()
      setTimeout(() => { window.URL.revokeObjectURL(url) })
    })
  } catch (e) {
    this.downBtnLoading = false
  }
},
usePromiseArr (data, rod) {
  const allPromise = []
  data.forEach(v => {
    allPromise.push(this.renderImg(v, rod))
  })
  return Promise.all(allPromise)
},
renderImg (data, rod) {
  return new Promise((resolve, reject) => {
    let num = 0
    const useSrc = `data:image/png;base64,${data.value}`
    const template2 = `
    <div class="title-normal">报修电话</div>
    <div class="title">${this.ruleForm.phoneNumber || 'xxxxxxxx'}</div>
    `
    const leftDiv = document.createElement('div')
    leftDiv.setAttribute('class', 'left downLeft')
    leftDiv.setAttribute('id', 'erweima-common')
    const header = document.createElement('div')
    header.setAttribute('class', 'left-header')
    const large1 = document.createElement('div')
    large1.setAttribute('class', 'font-large')
    large1.textContent = 'xxxx'
    const large2 = document.createElement('div')
    large2.setAttribute('class', 'font-large')
    large2.textContent = 'xxxx'
    const topImage = document.createElement('div')
    topImage.setAttribute('class', 'top-img')
    const img1 = document.createElement('img')
    img1.src = '/xxxxxx.png'
    img1.onload = () => {
      topImage.appendChild(img1)
      num++
      this.downloadImg(num, leftDiv, rod, data.key, resolve)
    }
    header.appendChild(large1)
    header.appendChild(topImage)
    header.appendChild(large2)
    leftDiv.appendChild(header)
    const safe = document.createElement('div')
    safe.setAttribute('class', 'safe')
    safe.textContent = 'xxxxxxxxxx'
    const borderDiv = document.createElement('div')
    borderDiv.setAttribute('class', 'left-border')
    const dashedDiv = document.createElement('div')
    dashedDiv.setAttribute('class', 'dashed-border')
    const Img2 = document.createElement('img')
    Img2.src = '/xxxxxxxx.png'
    Img2.onload = () => {
      dashedDiv.appendChild(Img2)
      num++
      this.downloadImg(num, leftDiv, rod, data.key, resolve)
    }
    const title1 = document.createElement('div')
    title1.setAttribute('class', 'title')
    title1.textContent = 'xxxx'
    const title2 = document.createElement('div')
    title2.setAttribute('class', 'title')
    title2.textContent = 'xxxxxxxxxx'
    const title3 = document.createElement('div')
    title3.setAttribute('class', 'title-min')
    title3.textContent = 'Area Under 24-hour Monitoring'
    borderDiv.appendChild(dashedDiv)
    borderDiv.appendChild(title1)
    borderDiv.appendChild(title2)
    borderDiv.appendChild(title3)
    const border2 = document.createElement('div')
    border2.setAttribute('class', 'left-border')
    border2.innerHTML = template2
    const small = document.createElement('div')
    small.setAttribute('class', 'title-small')
    small.textContent = `${this.ruleForm.producer || 'xxxxxxxxx'}`
    const leftcontent = document.createElement('div')
    leftcontent.setAttribute('class', 'left-content')
    const useImg = document.createElement('img')
    useImg.setAttribute('class', 'erwei')
    useImg.src = useSrc
    useImg.onload = () => {
      leftcontent.appendChild(useImg)
      leftcontent.appendChild(safe)
      leftcontent.appendChild(borderDiv)
      leftcontent.appendChild(border2)
      leftcontent.appendChild(small)
      leftDiv.appendChild(leftcontent)
      rod.appendChild(leftDiv)
      num++
      this.downloadImg(num, leftDiv, rod, data.key, resolve)
    }
  })
},
downloadImg (num, leftDiv, rod, name, resolve) {
  if (num !== 3) return
  const that = this
  domtoimage.toBlob(leftDiv).then(function (dataUrl) {
    rod.removeChild(leftDiv)
    that.zip.file(`${name}.jpeg`, dataUrl)
    resolve()
  })
}