无法遍历啊

<div class="col-md-9 threads-index main-col">
    <div class="panel panel-default">
        <div class="panel-heading">
            <div class="pull-left hidden-sm hidden-xs">
                <i class="fa fa-list"></i> 首页
            </div>
            <div class="clearfix"></div>
        </div>
        <div class="panel-body remove-padding-horizontal">
            <ul class="list-group row thread-list">
            </ul>
            <ul class="list-group row thread-list">
                {volist name="Topic" id="vo"}
                <li class="list-group-item media " style="margin-top: 0px;">
                    <div class="avatar pull-left">
                        <a href="post.html">
                            <img class="media-object img-thumbnail avatar-48" alt="imooc"
                                 src="<?=STATIC_URL;?>images/avatar.jpg"/>
                        </a>
                    </div>
                    <div class="infos">
                        <div class="media-heading">
                            <i class=""> {$vo.title}</i>
                            <a href="" title="">
                            </a>
                        </div>
                        <div class="media-body meta">
                            <a href="">
                                <span> 王丹的朋友圈被万达年会的图片、小视频霸屏了。
                                    这些都是她在万达的前同事从东方影都现场发出来的。
                                    王丹当时真有目迷五色、心醉神迷的感觉。大半年前，
                                    东方影都正式开业，王丹又是一通忙，然而彼时她已经没有了什么主人的感觉，
                                    因为2017年7月万达已将东方影都卖给了融创，随后在2018年10月，
                                    万达又将13个文旅城的服务主体——万达文旅管理公司作价60.81亿卖给了融创，
                                    王丹作为公司员工，也一起加盟了融创。</span>
                            </a>

              <span class="timeago" data-toggle="tooltip" data-placement="top"
                    title="">
              </span>
                        </div>
                    </div>
                </li>
                {\volist}
            </ul>

        </div>
    </div>
</div>

<?php

namespace app\index\controller;


class common extends Base
{
    public function topic_list()
    {
          //获取 留言板数据
        $Topic= model('Topic')->getTopics();

     return $this->fetch('',[
         'Topic'=>$Topic
     ]);
    }
}

model

public static function getTopic($id)
{
    $topic = self::find(['id' => $id]);
    //print_r(model("Topic")->getLastSql());die();
    return $topic;
}