使用el-upload不上传文件，触发不了http-reques

解决方案：放弃使用this.$refs.upload.submit(); 获取选择文件，使用FormData上传

<el-upload
  ref="upload"
  name="attachment"
  :limit="1"
  action=""
  :auto-upload="false"
  :on-exceed="onExceed"
  :on-change="onChange"
  :on-remove="onRemove">
  <el-link :underline="false" type="primary">选择文件</el-link>
</el-upload>

onExceed(files, fileList) {
    this.$message.error('只能上传一个文件')
},
onChange(file, fileList) {
    this.launchDialogForm.attachment = file.raw
},
onRemove(file, fileList) {
    this.launchDialogForm.attachment =null
}

var formData =new FormData()
formData.append('tradeNumber',this.launchDialogForm.tradeNumber)
formData.append('attachment',this.launchDialogForm.attachment)
createWorksheet(formData).then(response => {
   console.log(response)
})

export function createWorksheet(params) {
    return request({
       url:'/wo/create',
       method:'post',
       data: params
    })
}

后台：

@PostMapping("/create")
public ResponseResult createWorksheet(
             @RequestParam(value ="attachment",required =false) MultipartFile attachment,
             WorksheetParam param
) {
       return ResponseResult.success();
}