AJAX for C#.NET/VB.NET Programming

Introduction - What is AJAX?

AJAX, or Asynchronous JavaScript and XML, is a fancy way to use
JavaScript and XML to communicate with a web server without refreshing the web
page. You can visit this web page for more information about AJAX; it has a good
list of links.

Why use AJAX?

There are a couple of reasons to use AJAX in lieu of the traditional
form submission. The first is that it is very light weight: instead of sending
all of the form information to the server and getting all of the rendered HTML
back, simply send the data the server needs to process and get back only what
the client needs to process. Light weight means fast. The second reason to use
AJAX is because (as the logo in the link above makes clear) AJAX is cool.

Using AJAX with ASP.NET

Even though AJAX is a client side technology that uses JavaScript, the
client-server interaction is very important.

Adam Vandenberg has put together a nice JavaScript wrapper
for AJAX. His wrapper even does caching, although that will not be discussed
here. His wrapper is used in the code examples and project files.

Using the code

There are four parts of the code that are important to look at:

1. The HTML
   

   There are two form elements that will interact with AJAX. The input
   button "btn1" will invoke the AJAX code, which will make a
   server call and fill the select element "select1".

   
   
2. The JavaScript that calls the AJAX.
   

   The function getOptions() will do the main
   work.

   
   

   // Create the Request object (the AJAX wrapper)
   var request = new Request();
   // Change this to fit your environment
   var url = "http://localhost/ajax/";
   function getOptions()
   {
       // Call the AJAX
       // Notice the second parameter is actually a function to handle the
       // response
       request.GetNoCache(url + "requests/getOptions.aspx",
       function(result)
       {
           if (result.readyState!=ReadyState.Complete)
               return;             
           if (result.status==HttpStatus.OK && result.responseText != "")
           {
               // If the request was successfull and returned data
               var vals = result.responseText.split("~");
               for (i=0; i
   The ASPX file.
   The important thing here is that the aspx file only returns the
   string (XML) data from the code behind.
   <%@ Page language="c#"             Codebehind="getOptions.aspx.cs"             AutoEventWireup="false"             Inherits="ajax.requests.getOptions" %>
   <%=result%>
   
   The code behind. 
   protected string result = string.Empty;
   private void Page_Load(object sender, System.EventArgs e)
   {
       for (int i=0; i<10; result =" result.Substring(0,">

Labels: Ajax

# posted by Amit Patel @ 4:30 AM