怎么使用：自定义网站信息

我按照https://www.xunruicms.com/doc/744.html这个教程后台设置了上传图片的自定义字段

为啥后台调用不出来 上传的图片

<div class="form-group">
    <label class="col-md-2 control-label">首页关于我们右侧广告图</label>
    <div class="col-md-10">
        <?php echo dr_fieldform('{"name":"首页关于我们右侧广告图","fieldname":"adv_about","ismain":"1","fieldtype":"File","setting":{"option":{"ext":"jpg,gif,png","size":"1","attachment":"0","image_reduce":"","is_ext_tips":"0","css":""},"validate":{"required":"0","pattern":"","errortips":"","check":"","filter":"","formattr":"","tips":""}},"ismember":"1"}', $adv_about, 1, 1);?>
        <div class="files">
            <div class="file_row_html files_row">
                <div>
                    <div class="files_row_preview preview">
                        <a href="{dr_get_file(dr_site_info('adv_about'))}" target="_blank">
                            <img src="{dr_get_file(dr_site_info('adv_about'))} ">
                        </a>
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

这是我的代码