ASP.NET使用Jquery LigerUI 轮询方式配合Ajax实现消息推送

轮询是在客户端建立一个时钟，每隔一段时间对服务器发送一次请求，获取服务器数据，是实现消息推送最简单最易实现的一种方式，最大的缺点浏览器需要不断的向服务器发出请求，这样会占用很多的带宽，造成资源浪费

下面是JS代码：

$(document).ready(function () {
            setInterval(invoke, 20000);
        });
        function invoke() {
            var xhr = $.ajax({
                type: "POST",
                dataType: 'json',
                url: "Sys_msg.get_unRead_count.xhd",
                data: "",
                success: function (result) {
                    var obj = eval(result);
                    if (obj > msg_count)
                    {
                        $.ligerTip({
                            content: "您有<font color=red> " + (obj-msg_count) + "</font> 条新增未读消息，请注意查收！           <br> <a href='javascript:void(0)' onclick="window.top.f_addTab('Sys_msg','消息管理','personal/message/sys_msg.aspx')">进入处理</a>",
                             240,
                            //var winH = $(window).height(), winW = $(window).width();
                            x: tipW - 260,   //设置气泡位置，右下角气泡显示 
                            y: tipH - 80,
                            callback: function (t) {
                                var i = 10; //10秒倒计时
                                calctime(t, i);
                            }
                        });
                    }
                    msg_count = obj;
                    
                }
            });
        }
    var tipH = $(window).height(), tipW = $(window).width();    //获取屏幕尺寸
    function calctime(t, i) //这个函数用了递归来实现倒计时
        {
            i--;
            (i >= 0)
        ? setTimeout(function () {
            calctime(t, i);
        }, 1000)
        : $(t).remove();
        }

后台代码：

public class Sys_msg
    {
        public static BLL.Sys_msg msg = new BLL.Sys_msg();
        public static Model.Sys_msg model = new Model.Sys_msg();

        public HttpContext Context;
        public string emp_id;
        public string emp_name;
        public HttpRequest request;
        public string uid;
        

        public Sys_msg()
        {
        }

        public Sys_msg(HttpContext context)
        {
            Context = context;
            request = context.Request;

            var userinfo = new User_info();
            employee = userinfo.GetCurrentEmpInfo(context);

            emp_id = employee.id;
            emp_name = PageValidate.InputText(employee.name, 50);
            uid = PageValidate.InputText(employee.uid, 50);
            
        }


        public int get_unRead_count()
        {
            string serchtext = $" 1=1 ";
            //int rowcount = 0;
            serchtext += " and isRead=0";
            serchtext += " and UserID like N'%" + emp_id + "%'";
            DataSet ds = msg.GetList(serchtext);
            //rowcount = ds.Tables[0].Rows.Count;
            return ds.Tables[0].Rows.Count;
        }

    }