网站表单自定义参数之单文件字段不显示

创建表单自定义参数之单文件字段，开发者工具创建的字段

<div class="form-group">
    <label class="col-md-2 control-label">单文件</label>
    <div class="col-md-10">
        <?php echo dr_fieldform('{"name":"file","fieldname":"banner","ismain":"1","fieldtype":"File","setting":{"option":{"fieldtype":"","fieldlength":"","input":"1","ext":"jpg,gif,png,jpeg","size":"2","attachment":"0","image_reduce":"","is_ext_tips":"0","css":""},"validate":{"required":"0","pattern":"","errortips":"","check":"","filter":"","formattr":"","tips":""}},"ismember":"1"}', $file, 1, 1);?>
    </div>
</div>

最后显示成功，上传文件保存后，又没了？哪不对？