用elementUi中el-upload上传图片，之后要把图片数据和表单数据一起发送post请求给后台，表单数据后台可以取到，但是图片数据一直取不到请问是什么原因？

<div class="item-pic-bg">
    <img class="bgImg" :src="src" alt="背景图片">
        <el-upload
            class="upload"
            accept="image/*"
            :show-file-list="false"
            action="/upload/uploadFile"
            :on-success="handleSuccess">
        <el-button type="primary" @click="refeshLoad()" class="refesh btnNoBorder button b2">
        <i class="iconfont icon-shangchuan"></i> 点击上传
        </el-button>
        </el-upload>
</div>

//上传图片成功
            handleSuccess: function (response, file, fileList) {
                this.src = file.url;
                this.formData.files.push(file.raw);
            },
            
               //保存
            saveIt: function () {
                let formData = new FormData();
                formData.append('files', this.formData.files);
                //post请求         
                saveSlideShow(formData).then((res) => {
                })
            },