ajax学习笔记简单事例1完成验证

这个例子很简单，有一个输入框，onchange()事件触发验证.
html:

<HTML>
    <HEAD>
        <title>default</title>
        <meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
        <meta name="CODE_LANGUAGE" Content="C#">
        <meta name="vs_defaultClientScript" content="JavaScript">
        <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">

    </HEAD>
    <body MS_POSITIONING="GridLayout">
        <form id="Form1" method="post" runat="server">
            birthDate

            <input type=text id="birthDate" onchange="validate();"/>

            <div id="dateMessage"></div>
        </form>
        <script language="javascript">
var xmlHttp;

function validate()
{


   if(window.ActiveXObject)
   {
      xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
   }
   else if(window.XMLHttpRequest)
   {
     xmlHttp=new XMLHttpRequest();
   }

  var date=document.getElementById("birthDate");
  var url="validation.aspx?birthDate=" + escape(date.value);
  xmlHttp.open("GET",url,true);
  xmlHttp.onreadystatechange=callback;
  xmlHttp.send(null);
}
function callback()
{
  if(xmlHttp.readyState == 4)
  {
   if(xmlHttp.status == 200)
   {
     var mes=xmlHttp.responseXML.getElementsByTagName("message")[0].firstChild.data;
      var val=xmlHttp.responseXML.getElementsByTagName("passed")[0].firstChild.data;
     setMessage(mes,val);
   }
  }
}
function setMessage(message,isValid)
{

   var messageArea=document.getElementById("dateMessage");
   var fontColor="red";
   if(isValid=="true")
   {
     fontColor="green";

   }
   messageArea.innerHTML="<font color="+fontColor+" >"+message+"</font>";
}
        </script>
    </body>
</HTML>

validation.cs:

private void Page_Load(object sender, System.EventArgs e)
        {
            bool passed=validateDate(Request.QueryString["birthDate"].ToString());

            //this.Response.ContentType = "application/xml"; //
            this.Response.ContentType = "text/xml";
            //Response.Charset = "GB2312";
            this.Response.AppendHeader("Cache-Control","no-cache");
            string message="You have entered an invalid date";
            if(passed)
            {
                message="You have entered a valid date.";
            }

            this.Response.Write("<response>");
            this.Response.Write("<passed>"+passed.ToString().ToLower()+"</passed>");
            this.Response.Write("<message>"+message+"</message>");
            this.Response.Write("</response>");
　　        this.Response.End();

        }
        private bool validateDate(string date)
        {

                try
                {
                   Convert.ToDateTime(date);
                    return true;
                }
                catch
                {
                    return false;
                }


        }