如何实现滚动条滑到底部时自动加载更多内容

nbsp;html>


  <meta>
  <title></title>
  <script></script>
  <script>
    $(function () {
      AddSth();
    });
    $(function () {
      $(".main").unbind("scroll").bind("scroll", function (e) {
        var sum = this.scrollHeight;
        if (sum <= $(this).scrollTop() + $(this).height()) {
          AddSth();
        }
      });
    });
    function AddSth() {
      $.ajax({
        type: &#39;POST&#39;,
        url: "index.aspx/ReturnSth",
        dataType: "json",
        contentType: "application/json; charset=utf-8",
        //data: "",
        success: function (data) {
          json = $.parseJSON(data.d);
          for (var i in json) {
            var tbBody = "<ul><li>" + json[i].sth + "";
            $(".main").append(tbBody);
          }
          $(".main").append("<hr />");
        }
      });
    }
  </script>