Changing XML node value

This script should change the TOP value of the specified COMMUNITY node. But it doesn't what could be wrong?

<?php

function make_update( $nodeid, $name, $top, $left, $width, $height ) {

$nodes = new SimpleXMLElement('communities.xml', null, true);

$node = $nodes->xpath("//COMMUNITY[@ID='$nodeid']"); 

$node->TOP->nodeValue = $top;

$nodes->asXML();

return $top;
}

echo make_update(trim($_REQUEST['nodeid']),trim($_REQUEST['name']),trim($_REQUEST['top']),trim($_REQUEST['left']),trim($_REQUEST

['width']),trim($_REQUEST['height']));

?>

The XML looks like this.

<?xml version="1.0" encoding="ISO-8859-1"?>
<COMMUNITIES>
<COMMUNITY ID="c001">
  <NAME>Town Services</NAME> 
  <TOP>50</TOP> 
  <LEFT>50</LEFT> 
  <WIDTH>200</WIDTH> 
  <HEIGHT>300</HEIGHT> 
  <URLS>
      <URL ID="U001">
          <NAME>Google.com</NAME>
          <URLC>http://www.google.com</URLC>
      </URL>
      <URL ID="U002">
          <NAME>Bing.com</NAME>
          <URLC>http://www.bing.com</URLC>
      </URL>
      <URL ID="U003">
          <NAME>Yahoo.com</NAME>
          <URLC>http://www.yahoo.com</URLC>
      </URL>
      开发者_开发问答<URL ID="U004">
          <NAME>Aol.com</NAME>
          <URLC>http://www.aol.com</URLC>
      </URL>
  </URLS> 
  </COMMUNITY>
</COMMUNITIES>

First, you should adjust the code that gets the desired COMMUNITY element. The xpath method returns an array of SimpleXMLElement objects, representing the elements that matched your search string.

Example:

$returnArray = $nodes->xpath("//COMMUNITY[@ID='$nodeid']"); 
$node = $returnArray[0];

Second, to modify the value of the TOP element, set directly to TOP itself:

// This replaces the contents of the TOP element with $top
$node->TOP = $top;

// This appends '<nodeValue>$top</nodeValue>' to the contents of TOP
$node->TOP->nodeValue = $top;