1.安装elementUI：npm i element-ui -S

2.引入elementUI组件（main.js文件）

import Element from 'element-ui'
import 'element-ui/lib/theme-chalk/index.css'

Vue.use(Element, { size: 'small' })

3.访问Element官网【组件–Upload上传】

<el-upload
  action="https://jsonplaceholder.typicode.com/posts/"
  list-type="picture-card"
  :on-preview="handlePictureCardPreview"
  :on-remove="handleRemove">
  <i class="el-icon-plus"></i>
</el-upload>
<el-dialog :visible.sync="dialogVisible">
  <img width="100%" :src="dialogImageUrl" alt="">
</el-dialog>
<script>
  export default {
    data() {
      return {
        dialogImageUrl: '',
        dialogVisible: false
      };
    },
    methods: {
      handleRemove(file, fileList) {
        console.log(file, fileList);
      },
      handlePictureCardPreview(file) {
        this.dialogImageUrl = file.url;
        this.dialogVisible = true;
      }
    }
  }
</script>

4.我的需求：点击保存按钮手动上传，只能上传一张图片，参数为userId

5.script中的data( )和methods( )如下：

<script>
  export default {
    data() {
      return {
      	file:'',
        dialogImageUrl: '',
        dialogVisible: false,
        imgUrl:'',
        userId: '',
        uid:'',
        
        // 上传图片时附带的额外参数userId
        resData:{
        	userId: window.localStorage["userId"]
        },
      };
    },
    methods: {
      handleRemove(file, fileList) {
        console.log(file, fileList);
      },
      handlePictureCardPreview(file) {
        this.dialogImageUrl = file.url;
        this.dialogVisible = true;
      },
      
      // 点击保存按钮上传图片
      submit2:function(res){
		this.$refs.upload.submit();
	},
		
	// 图片上传成功后，后台返回图片的路径
	onSuccess:function(res){
		// console.log(res);
		if(res.status==200){
			this.imgUrl=res.data.imgUrl;
		}
	},
    }
  }
</script>

6.该组件的效果图如下：