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AJAX for ASP.NET

, 28 Jun 2005
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An easy way to use AJAX with ASP.NET.

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".

    <select id="select1"></select>
    <input id="btn1" value="Fill Select" type="button" <BR>       onclick="getOptions();">
  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 <BR>    // 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<vals.length; i++)
                {
                    var pair = vals[i].split("|");
                    var op = new Option(pair[1], pair[0], false, false);
                    var sel = document.getElementById("select1");
                    sel.options[sel.length] = op;
                }
                alert("Remember that the new values in form" + 
                      " element 'select1' are not in viewstate." + 
                      " Code appropriately.");
            }
            else
            {
                // Handle the failure condition
                alert('Get options failed.');
            }
        }
        )
    }
  3. 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%>
  4. The code behind.
    protected string result = string.Empty;
    private void Page_Load(object sender, System.EventArgs e)
    {
        for (int i=0; i<10; i++)
        {
            result += i.ToString() + "|option " + i.ToString() + "~";
        }
        // to drop the last '~'
        result = result.Substring(0, result.Length - 1); <BR>}

What's Next

As you can see, it is very easy to have a lightweight AJAX component interact with ASP.NET. I know what you are thinking: "Steve, wait a minute: I thought you had to use XML to use AJAX?" From the example, you can see that the string being returned is a pipe and tilde delimited string. You do not have to use XML. There are a lot of places where XML would be very useful, but using this implementation it is not required.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Steven A Bristol
Web Developer
United States United States
No Biography provided

Comments and Discussions

 
Questionajx solution Pingroupbhagwat prasad14-Feb-12 5:53 
GeneralMy vote of 1 Pinmemberubaid215-Jul-10 20:00 
GeneralYou can see PinmemberChiranjibC7-Feb-07 1:28 
GeneralRe: You can see PinmemberIslam94-Nov-07 0:53 
GeneralHav you tried... PinmemberDoodie Woddy Doodlechips24-Jan-07 2:00 
GeneralTurn ASP.NET controls into AJAXenabled controls PinmemberOmegaCD8-Jul-06 20:45 
GeneralRe: Turn ASP.NET controls into AJAXenabled controls PinmemberSteven A Bristol9-Jul-06 2:33 
GeneralUse the Ajax.NET library, not any of the advertisement messages trolls have left here. PinmemberSteven A Bristol27-Jun-06 12:24 
GeneralIs AJAX all about js PinmemberSyed Moshiur Murshed20-May-06 4:32 
Generalrequest is null or not an object PinmemberShri Pal31-Mar-06 22:03 
GeneralRe: request is null or not an object PinmemberShri Pal31-Mar-06 22:08 
GeneralRe: request is null or not an object Pinmemberzhongguosou2-May-06 16:10 
GeneralRe: request is null or not an object Pinmemberzhongguosou2-May-06 16:42 
GeneralRe: request is null or not an object PinmemberDiamond1120-Aug-06 23:16 
Generalthank you Pinmemberminhhai_cd@yahoo.com2-Mar-06 21:34 
NewszumiPage for ASP.NET PinmemberAmir L.21-Dec-05 13:01 
GeneralComfortASP.NET Pinmemberdazei22-Sep-05 6:39 
GeneralThe code presented is very amateurish PinmemberDmitri Kirillov10-Jul-05 6:12 
GeneralAspnet Newbies here, need help open project. PinsussKhmerKid30-Jun-05 22:16 
GeneralRe: Aspnet Newbies here, need help open project. Fixed Pinmemberkhmerkidnow30-Jun-05 22:38 
Generalajax.net - The free library for .net (c#) Pinmemberploufs29-Jun-05 2:12 
GeneralRe: ajax.net - The free library for .net (c#) PinmemberJohn Rayner17-Oct-05 12:12 

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