详解Element-UI中上传的文件前端处理

2019-11-19 11:03:51

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Element-UI对于文件上传组件的功能点着重于文件传递到后台处理，所以要求action为必填属性。但是如果需要读取本地文件并在前端直接处理，文件就没有必要传递到后台，比如在本地打开一个JSON文件，利用JSON文件在前端进行动态展示等等。
下面就展示一下具体做法：

首先定义一个jsonContent, 我们的目标是将本地选取的文件转换为JSON赋值给jsonContent

然后我们的模板文件是利用el-dialog和el-upload两个组件组合：这里停止文件自动上传模式:auto-upload="false"

 <el-button type="primary" @click="dialogVisible = true">Load from File</el-button> <el-dialog title="Load JSON document from file" :visible.sync="dialogVisible">  <el-upload :file-list="uploadFiles" action="alert" :auto-upload="false" multiple :on-change="loadJsonFromFile">   <el-button size="small" type="primary">Select a file</el-button>   <div slot="tip">upload only jpg/png files, and less than 500kb</div>  </el-upload>  <span slot="footer">   <el-button type="primary" @click="dialogVisible = false">cancel</el-button>   <el-button type="primary" @click="loadJsonFromFileConfirmed">confirm</el-button>  </span> </el-dialog>

最后通过html5的filereader对变量uploadFiles中的文件进行读取并赋值给jsonContent

if (this.uploadFiles) {    for (let i = 0; i < this.uploadFiles.length; i++) {     let file = this.uploadFiles[i]     console.log(file.raw)     if (!file) continue     let reader = new FileReader()     reader.onload = async (e) => {      try {       let document = JSON.parse(e.target.result)       console.log(document)      } catch (err) {       console.log(`load JSON document from file error: ${err.message}`)       this.showSnackbar(`Load JSON document from file error: ${err.message}`, 4000)      }     }     reader.readAsText(file.raw)    }   }

为方便测试，以下是完整代码：

另外一篇文章是介绍如何将jsonContent变量中的JSON对象保存到本地文件

<template> <div>  <el-button type="primary" @click="dialogVisible = true">Load from File</el-button> <el-dialog title="Load JSON document from file" :visible.sync="dialogVisible">  <el-upload :file-list="uploadFiles" action="alert" :auto-upload="false" multiple :on-change="loadJsonFromFile">   <el-button size="small" type="primary">Select a file</el-button>   <div slot="tip">upload only jpg/png files, and less than 500kb</div>  </el-upload>  <span slot="footer">   <el-button type="primary" @click="dialogVisible = false">cancel</el-button>   <el-button type="primary" @click="loadJsonFromFileConfirmed">confirm</el-button>  </span> </el-dialog></div> </template> <script>export default { data () {  return {   // data for upload files   uploadFilename: null,   uploadFiles: [],   dialogVisible: false  } }, methods: {  loadJsonFromFile (file, fileList) {   this.uploadFilename = file.name   this.uploadFiles = fileList  },  loadJsonFromFileConfirmed () {   console.log(this.uploadFiles)   if (this.uploadFiles) {    for (let i = 0; i < this.uploadFiles.length; i++) {     let file = this.uploadFiles[i]     console.log(file.raw)     if (!file) continue     let reader = new FileReader()     reader.onload = async (e) => {      try {       let document = JSON.parse(e.target.result)       console.log(document)      } catch (err) {       console.log(`load JSON document from file error: ${err.message}`)       this.showSnackbar(`Load JSON document from file error: ${err.message}`, 4000)      }     }     reader.readAsText(file.raw)    }   }   this.dialogVisible = false  } }}</script>

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