wordpress上一篇/下一篇文章显示没有了

         <span class="pre"><?php
      if (get_previous_post()) {     echo '上一篇：';    previous_post_link('%link');  } else {     echo "已经是最新文章了";  }
     ?> </span>

     <span class="next">
     <?php
      if (get_next_post()) {     echo '下一篇：';    next_post_link('%link');  } else {     echo "已经是最新文章了";  }
     ?>
     </span>