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：

 1 $(document).ready(function () {
 2             setInterval(invoke, 20000);
 3         });
 4         function invoke() {
 5             var xhr = $.ajax({
 6                 type: "POST",
 7                 dataType: 'json',
 8                 url: "Sys_msg.get_unRead_count.xhd",
 9                 data: "",
10                 success: function (result) {
11                     var obj = eval(result);
12                     if (obj > msg_count)
13                     {
14                         $.ligerTip({
15                             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>",
16                              240,
17                             //var winH = $(window).height(), winW = $(window).width();
18                             x: tipW - 260,   //设置气泡位置，右下角气泡显示 
19                             y: tipH - 80,
20                             callback: function (t) {
21                                 var i = 10; //10秒倒计时
22                                 calctime(t, i);
23                             }
24                         });
25                     }
26                     msg_count = obj;
27                     
28                 }
29             });
30         }
31     var tipH = $(window).height(), tipW = $(window).width();    //获取屏幕尺寸
32     function calctime(t, i) //这个函数用了递归来实现倒计时
33         {
34             i--;
35             (i >= 0)
36         ? setTimeout(function () {
37             calctime(t, i);
38         }, 1000)
39         : $(t).remove();
40         }

后台代码：

 1 public class Sys_msg
 2     {
 3         public static BLL.Sys_msg msg = new BLL.Sys_msg();
 4         public static Model.Sys_msg model = new Model.Sys_msg();
 5 
 6         public HttpContext Context;
 7         public string emp_id;
 8         public string emp_name;
 9         public HttpRequest request;
10         public string uid;
11         
12 
13         public Sys_msg()
14         {
15         }
16 
17         public Sys_msg(HttpContext context)
18         {
19             Context = context;
20             request = context.Request;
21 
22             var userinfo = new User_info();
23             employee = userinfo.GetCurrentEmpInfo(context);
24 
25             emp_id = employee.id;
26             emp_name = PageValidate.InputText(employee.name, 50);
27             uid = PageValidate.InputText(employee.uid, 50);
28             
29         }
30 
31 
32         public int get_unRead_count()
33         {
34             string serchtext = $" 1=1 ";
35             //int rowcount = 0;
36             serchtext += " and isRead=0";
37             serchtext += " and UserID like N'%" + emp_id + "%'";
38             DataSet ds = msg.GetList(serchtext);
39             //rowcount = ds.Tables[0].Rows.Count;
40             return ds.Tables[0].Rows.Count;
41         }
42 
43     }