asp.net 2.0 ajax中实现弹出窗口报警提示

  在 web应用中，比如OA中，经常要用到一些提示，比如EMAIL到达了，就做个象MSN那样的提示框，弹出给用户提示，然后
再关闭。在asp.net 2.0的ajax中，这个现在不难做到了，刚好看到老外的一篇文章，讲解到，下面小结之
（原文：http://aspalliance.com/1306_How_to_Show_MessengerLike_Popups_Using_AJAX）

  比如有个数据库表，是存放EMAIL的，当数据库表中的EMAIL一有的时候，就提示用户，首先简单写一个WEBSERVICE如下
[ScriptService]
public class InboxService : System.Web.Services.WebService
{
    [WebMethod]
    public int GetLatestNumberOfEmails()
    {
        int numberOfEmails = 0;

        using (SqlConnection conn = new SqlConnection(WebConfigurationManager.ConnectionStrings[0].ConnectionString))
        {
            using (SqlCommand cmd = new SqlCommand("GetLatestNumberOfEmails", conn))
            {
                cmd.CommandType = CommandType.StoredProcedure;

                conn.Open();
                numberOfEmails = (int)cmd.ExecuteScalar();
            }
        }

        return numberOfEmails;
    }
}
这里要注意要在客户端通过AJAX调用WEBSERICE，要加上[ScriptService]

2 在default.aspx中，首先加入一个updateprogress控件，如下
 <asp:UpdateProgress DynamicLayout="False" ID="UpdateProgress1" runat="server">
    <ProgressTemplate>
        <div >
            var numberOfEmails_original= 0;
           
            var app = Sys.Application;
            app.add_init(applicationInitHandler);
           
            function applicationInitHandler(sender, args) {
                InboxService.GetLatestNumberOfEmails(OnCurrentNumberOfEmailsReady);
      }



首先，默认的当然是0封邮件了，有变量来存放当前邮件数量，
之后是在ajax中的初始化事件中调用webserice的方法了，并且回调OnCurrentNumberOfEmailsReady方法，

      function OnCurrentNumberOfEmailsReady(result, userContext, methodName) {
                numberOfEmails_original= result;

                // Start Checking
                StartChecking();
            }

OnCurrentNumberOfEmailsReady方法将WEBSERVICE调用的结果（当前状态下有多少封信RESULT）返回给变量，然后调用sartchecking()方法

      function StartChecking() {
          InboxService.GetLatestNumberOfEmails(OnLastestNumberOfEmailsReady);
      }

startchecking方法，继续回调OnLastestNumberOfEmailsReady方法

            function OnLastestNumberOfEmailsReady(result, userContext, methodName) {
                var numberOfEmails_new= result;
                if (numberOfEmails_new > numberOfEmails_original) {
                    ShowPopup();
                    $get("modalBody").innerHTML= numberOfEmails_new - numberOfEmails_original;
                   
                    // Update the count here
                    numberOfEmails_original= numberOfEmails_new;
                }

                // Start checking again
                window.setTimeout(StartChecking, 10000);
            }

这个方法，用当前邮件数-原来邮件数，就得出新增了多少封邮件了，再将结果赋值给显示区域的modalbody，并且记得把当前邮件数量的
变量更新哦（numberOfEmails_original= numberOfEmails_new;
）

然后再用setimeout来设置每隔10000毫秒检查一次了

            function ShowPopup() {
                $get("UpdateProgress1").style.visibility= "visible";
                $get("UpdateProgress1").style.display= "block";
            }
            function HidePopup() {
                $get("UpdateProgress1").style.visibility= "hidden";
                $get("UpdateProgress1").style.display= "none";
            }
        </script>