vue + elementUI——upload传数据给后台出错后再次点击upload无效

 <el-upload
 　　ref="upload_file"
    action=""
    :multiple="false"
    :limit="1"
    :show-file-list="false"
    :on-change="importExcel"
    :auto-upload="false">
    　　<el-button
        　　:loading="btnLoading"
            type="primary">
            本地上传
        </el-button>
</el-upload>

importExcel(response) {
        let _this = this;
        _this.$refs.upload_file.clearFiles();  // <==
        ···
}