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Populate a text box with ajax from Php file

I need to dynamically populate a text box with a variable that is inside a php file.
There is a php file that when you choose from a combo box a certain value it goes(Ajax) to another php file and retrieve another certain value that is inside a Switch depending on the value determined form the combo box and display it on the text box that it is already next to the combo box in the same page.
Thanks in advance.
Some code would be appreciated.
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doRodrigo
Asked:
doRodrigo
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1 Solution
 
Ray PaseurCommented:
Here is a teaching example that I have had in my code library for some time.  I think it may be attributable to Rasmus Lerdorf, of PHP fame.  Worth reading so you can get a basic understanding of the technology.  Then you might want to look into jQuery for a specific solution.

Best regards, ~Ray
I find a lot of this AJAX stuff a bit of a hype.  Lots of people have
been using similar things long before it became "AJAX".  And it really
isn't as complicated as a lot of people make it out to be.  Here is a
simple example from one of my apps.  
 
/* THE JAVASCRIPT TO CREATE THE AJAX INFRASTRUCTURE */
/* FUNCTION TO CREATE THE BROWSER-DEPENDENT REQUEST OBJECT */
function createRequestObject() 
{
    var ro;
    var browser = navigator.appName;
    if(browser == "Microsoft Internet Explorer")
    {
        ro = new ActiveXObject("Microsoft.XMLHTTP");
    }else
    {
        ro = new XMLHttpRequest();
    }
    return ro;
}
 
 
/* FUNCTION TO SEND THE REQUEST */
function sendReq(action) 
{
    http.open('get', 'ajaxprocessor.php?action='+action);
    http.onreadystatechange = handleResponse;
    http.send(null);
}
 
 
/* FUNCTION TO HANDLE THE RESPONSE */
function handleResponse()
{
    if(http.readyState == 4)
    {
        var response = http.responseText;
        var update = new Array();
 
        if(response.indexOf('|' != -1))
        {
            update = response.split('|');
            document.getElementById(update[0]).innerHTML = update[1];
        }
    }
}
 
 
/* CREATE THE OBJECT */
var http = createRequestObject();
 
/* END OF THE JAVASCRIPT */
 
This creates a request object along with a send request and handle
response function.  So to actually use it, you could include this js in
your page.  Then to make one of these backend requests you would tie it
to something.  Like an onclick event or a straight href like this:
 
<a href="javascript:sendReq('foo')">[Foo]</a>
 
That means that when someone clicks on that link what actually happens
is that a backend request to ajaxprocessor.php?action=foo will be sent.
 
In ajaxprocessor.php you might have something like this:
 
/* THE PHP TO HANDLE THE REQUEST FROM THE FRONT-END SCRIPT */
switch($_GET['action']) 
{
    case 'foo':
      // DO WHATEVER PROCESSING IS APPROPRIATE
      // THEN RETURN A RESPONSE STRING TO handleResponse()
      echo "foo|Foo done";
      break;
      // ETC...
}
 
Now, look at handleResponse.  It parses the "foo|Foo done" string and
splits it on the '|' and uses whatever is before the '|' as the dom
element id in your page and the part after as the new innerHTML of that
element.  That means if you have a div tag like this in your page:
 
<div id="foo">Waiting for Foo</div>
 
Once you click on that link, that will dynamically be changed to:
 
<div id="foo">Foo done</div>
 
That's all there is to it.  Everything else is just building on top of
this.  Replacing my simple response "id|text" syntax with a richer XML
format and making the request much more complicated as well.  Before you
blindly install large "AJAX" libraries, have a go at rolling your own
functionality so you know exactly how it works and you only make it as
complicated as you need.  Often you do not need much more than what I
have shown here.
 
Expanding this approach a bit to send multiple parameters in the
request, for example, would be really simple.  Something like:
 
function sendReqArg(action,arg) 
{
    http.open('get', 'ajaxprocessor.php?action='+action+'&arg='+arg);
    http.onreadystatechange = handleResponse;
    http.send(null);
}
 
And your handleResponse can easily be expanded to do more interesting 
things than just replacing the contents of a div.
 
-Rasmus (Lerdorf?)

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doRodrigoAuthor Commented:
Ray_Paseur, as usual you were fast but I don't know if my mind is completely shut down but I couldn't understand it at all...

Could you comment on the code you sent, this way I could get a glimpse at what you wanted to say in the lines that are written above...

Thanks for the patience...
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Ray PaseurCommented:
Well, there are already a lot of comments in Rasmus' code example, but I will try to add a little.

Basically you need two things for AJAX to work.  The first thing is a web page with some JS in it.  The other thing is a backend script that gets control from the JS via the sendReq() function.

There are three parts of the JS.  One part creates the request object (lines 8-20).  The next part sends the request object (lines 23-29).  The last part listens for the response and changes the DIV in the DOM (lines 32-46).

The listener part of the JS manipulates the DOM, adding the "innerHTML" to a DIV whenever it is triggered.  

A specific trigger action occurs at the link on line 59.

If you do not understand it at first, be patient with yourself.  This is about as simple as AJAX can be made (there are a lot of moving parts) and it takes a while to step through all the pieces.  Don't get discouraged.  Just follow the variable names carefully and I am sure you will see it after a few minutes.

best, ~Ray
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doRodrigoAuthor Commented:
Thanks! That actually helped a lot.
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Ray PaseurCommented:
Thanks for the points!  Best, ~Ray
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