PHP Example - AJAX and XML
AJAX can be used for interactive communication with an XML
file.
AJAX XML example
The following example will demonstrate how a web page can fetch
information from an XML file with AJAX technology.
CD info will be listed here...
Example explained - The HTML page
The HTML page contains a link to an external JavaScript, an HTML form, and a
div element:
<html>
<head>
<script type="text/javascript" src="selectcd.js"></script>
</head>
<body>
<form>
Select a CD:
<select name="cds" onchange="showCD(this.value)">
<option value="Bob Dylan">Bob Dylan</option>
<option value="Bonnie Tyler">Bonnie Tyler</option>
<option value="Dolly Parton">Dolly Parton</option>
</select>
</form>
<div id="txtHint"><b>CD info will be listed here...</b></div>
</body>
</html> |
As you can see it is just a simple HTML form with a simple drop down box called "cds".
The <div> below the form will be
used as a placeholder for info retrieved from the web server.
When the user selects data, a function called "showCD" is executed. The
execution of the function is triggered by the "onchange" event. In other words:
Each time the user change the value in the drop down box, the function showCD is called.
Example explained - The JavaScript code
This is the JavaScript code stored in the file "selectcd.js":
var xmlhttp
function showCD(str)
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
{
alert ("Your browser does not support AJAX!");
return;
}
var url="getcd.php";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlhttp.onreadystatechange=stateChanged;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}
function stateChanged()
{
if (xmlhttp.readyState==4)
{
document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
}
}
function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
{
// code for IE7+, Firefox, Chrome, Opera, Safari
return new XMLHttpRequest();
}
if (window.ActiveXObject)
{
// code for IE6, IE5
return new ActiveXObject("Microsoft.XMLHTTP");
}
return null;
} |
The stateChanged() and GetXmlHttpObject functions are the same as in the
PHP AJAX Suggest chapter, you can go
to there for an explanation of those.
The showCD() Function
When a CD in the drop-down box is selected, the showCD() function
executes the following:
- Calls the GetXmlHttpObject() function to create an XMLHTTP object
- Defines an URL (filename) to send to the server
- Adds a parameter (q) to the URL with the content of the drop-down box
- Adds a random number to prevent the server from using a cached file
- Each time the readyState property changes, the stateChanged() function
will be executed
- Opens the XMLHTTP object with the given URL
- Sends an HTTP request to the server
Example explained - The PHP Page
The server paged called by the JavaScript, is a PHP file called
"getcd.php".
The PHP script loads an XML document, "cd_catalog.xml", runs a query against the XML file, and returns the result as HTML:
<?php
$q=$_GET["q"];
$xmlDoc = new DOMDocument();
$xmlDoc->load("cd_catalog.xml");
$x=$xmlDoc->getElementsByTagName('ARTIST');
for ($i=0; $i<=$x->length-1; $i++)
{
//Process only element nodes
if ($x->item($i)->nodeType==1)
{
if ($x->item($i)->childNodes->item(0)->nodeValue == $q)
{
$y=($x->item($i)->parentNode);
}
}
}
$cd=($y->childNodes);
for ($i=0;$i<$cd->length;$i++)
{
//Process only element nodes
if ($cd->item($i)->nodeType==1)
{
echo($cd->item($i)->nodeName);
echo(": ");
echo($cd->item($i)->childNodes->item(0)->nodeValue);
echo("<br />");
}
}
?>
|
When the CD query is sent from the JavaScript to the PHP page, the following
happens:
- PHP creates an XML DOM object
- Find all <artist> elements that matches the
name sent from the JavaScript
- Output the album information (send to the "txtHint" placeholder)
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