如何使用php编辑xml子节点

i already search here before i ask this question.. I know there is an answer here somewhere.. but i can't find it..

I want to be able to edit child node by id in my xml file.. i tried alot of script but i'm having a really bad time with this..

please see this line in edit.php:

echo "the problem is in the next line";

this is the last line that the server reads..

thanks you for your help.

events.xml

<?xml version="1.0" encoding="UTF-8" ?>
<events>
    <record>
        <id>1</id>
        <event>a</event>
        <eventDate>a</eventDate>
        <desc>a</desc>
    </record>
    <record>
        <id>2</id>
        <event>b</event>
        <eventDate>b</eventDate>
        <desc>b</desc>
    </record>
</events>

edit.php

header("Content-type: text/html; charset=utf-8");

$record = array(
    'id' => $_POST['id'],
    'event' => $_POST['event'],
    'eventDate' => $_POST['eventDate'],
    'desc' => $_POST['desc'],
);

$id = $record["id"];
$dom = new DOMDocument;
$dom->load('events.xml');

$xpath = new DOMXPath($dom);
$query = sprintf('/events/record[./id = "%d"]', $id);

foreach($xpath->query($query) as $record) {

    $eventN = $record->parentNode->getElementsByTagName("event");
    echo "the problem is in the next line";
    $eventN->item(0)->nodeValue = $record["event"];

    $dateN = $record->parentNode->getElementsByTagName("eventDate");
    $dateN->item(0)->nodeValue = $record["eventDate"];

    $descN = $record->parentNode->getElementsByTagName("desc");
    $descN->item(0)->nodeValue = $record["desc"];

}
$dom->save("events.xml");
header("Location: {$_SERVER['HTTP_REFERER']}");
?>

Edited: Working edit.php but not dynamic

<?php
header("Content-type: text/html; charset=utf-8");

$record = array(
    'id' => $_POST['id'],
    'event' => $_POST['event'],
    'eventDate' => $_POST['eventDate'],
    'desc' => $_POST['desc'],
);

$id = $record["id"];
$dom = new DOMDocument;
$dom->load('events.xml');

$xpath = new DOMXPath($dom);
$query = sprintf('/events/record[./id = "%d"]', $id);

foreach($xpath->query($query) as $record) {

    $eventN = $record->parentNode->getElementsByTagName("event");
    echo "i change it to string text and it's works. ";
    $eventN->item(0)->nodeValue = 'text';

    $dateN = $record->parentNode->getElementsByTagName("eventDate");
    $dateN->item(0)->nodeValue = 'text';

    $descN = $record->parentNode->getElementsByTagName("desc");
    $descN->item(0)->nodeValue = 'text';

}
$dom->save("events.xml");
header("Location: {$_SERVER['HTTP_REFERER']}");
?>