PHP undefined method DOMNodeList::setAttribute() - php

Question

I get this error message from PHP: "undefined method DOMNodeList::setAttribute()" from line 9. I am trying to change the src of an image in my HTML at my server and so far this is my code:
<?php
if (isset($_POST['id']) && isset($_POST['name']))
{
$id = $_POST['id'];
$name = $_POST['name'];
$html = $_POST['html'];
$dom = new domDocument;
$dom->loadHTML($html);
$node = $dom->getElementsByTagName( 'img' );
$node ->setAttribute('src', 'images/' . $name);//line 9
echo $dom->saveHTML();
}
echo 'error';
exit;
//html
<div><img id="picture" src=""></div>
The variable 'id' is the HTML id of the specific line of HTML, name is the the name of the image and HTML is the line of HTML.
As far as I can understand from researching I select a specific line of HTML which I then load to my DOM variable. I then specify the element ie: "img" which I can then edit through the use of setAttribute however this does not work. I only want to change the source of this one img with the ID of "picture".

Answer 1

But the DOMNodeList doesn't have that method.
getElementsByTagName is part of the DOMDocument class.
You don't need to cast anything, just call the method:
$links = $dom->getElementsByTagName('a');
foreach ($links as $link) {
$spans = $link->getElementsByTagName('span');
}
And by the way, DOMElement is a subclass of DOMNode. If you were talking about a DOMNodeList, then accessing the elements in such a list can be done, be either the method presented above, with a foreach loop, either by using the item() method of DOMNodeList
$link_0 = $dom->getElementsByTagName('a')->item(0);

Answer 2

getElementsByTagName returns a list of nodes. Just try with:
$nodes = $dom->getElementsByTagName('img');
foreach ($nodes as $node) {
$node->setAttribute('src', 'images/' . $name);
}