上拉加载（方式二）

public function newsajax(){
        $num = $_GET['num'];
        $catid= $_GET['catid'];
         if (!$catid) {
             //如果不带ID则获取排序最先一个
             $acats = $this->db->getOne("SELECT * FROM " . TABLE_PREFIX . "acat WHERE is_show = 1 ORDER BY sort ASC ");
             $catid=$acats['cat_id'];
         }
        $news = $this->db->getAll("SELECT * FROM ".TABLE_PREFIX."article WHERE is_show = 1 AND  cat_id='$catid'  ORDER BY a_id DESC limit $num, 6 ");
        foreach ($news as $key => $value) {
            $news[$key]['created'] = date("Y-m-d",$value['created']);
            $news[$key]['title'] = mb_substr($value['title'], 0,20,'utf-8');

        }
        
        echo json_encode($news);
    }

$(window).scroll(function () { //执行监视滚动条事件

    if ($(window).scrollTop() >=$(document).height() - $(window).height()) { //判断滚动是否到达底部
      var num = $("#num").attr("num");//获取当前数量
      var num1 = parseInt(num)+6;//获取获取当页最高数
      $("#num").attr("num",num1)//把最高数赋值给#num
       $.ajax({
                cache: true,
                type: "POST",
                dataType:"json",
                url:"{PURL('news/newsajax?num="+num+"&catid='.$catid)}",
                async: false,
                error: function(request) {
                },
                 beforeSend:function(){
                    $("#ajaxlogin").show();
                },

                success: function(data) {
                    if (data=="") {
                      $("#ajaxlogin").html("已经加载完了");
                    }else{
                        var data=eval(data);
                            setTimeout(function(){
                              $("#ajaxlogin").hide();
                            $.each( data, function( key, value ) {
                                 var str = data[key]['mktp'];
                                 var mm='<li class="news-li bgw"><a href="{PURL("news/new_con?id=' +data[key]['a_id']+ '")}" class="news-li-a">{if $v.mktp}<img src="' +data[key]['mktp']+ '" class="new-pic">{else}<img src="{$t_url}images/k-4.jpg" class="new-pic">{/if}<div class="new-li-r"><h3>' +data[key]['title']+ '</h3><p class="gray fz12 news-date"><span class="time">' +data[key]['created']+ '</span></p></div></a></li>';
                                $(mm).appendTo('#num ul');
                            });  
                        },1000);
                    }
                }
            });
    } else {
       
    }
});