php DOM getAttribute

Question

Alright, so I have an odd case here that I just can't figure out.

I want to parse a list on a website. The HTML looks somewhat like this:

<!-- ... -->
<ul id="foo">
    <li data-text="item 1">Blabla</li>
    <li data-text="item 2">Blabla</li>
    <li data-text="item 3">Blabla</li>
    <li data-text="item 4">Blabla</li>
</ul>
<!-- ... -->

Now I want to grab all the list items. I use the DOMDocument-class for that. So far, that works out just fine:

$dom = new DOMDocument();

if (!$dom->loadHTML($html)) {
    die ('Could not parse...');
}

$list = $dom->getElementById('foo');
$items = $list->childNodes;
foreach ($items as $item) {
     print_r($item);
}

But now, I'm looking for a simple method to read out the data-text attribute. What I did was:

foreach ($items as $item) {
     echo $item->getAttribute('data-text');
}

This works just fine for the very first item, but then it crashes the foreach-loop. The output is:

item 1
Fatal error: Call to undefined method DOMText::getAttribute() in example.php on line 44

What I don't get here is how calling the getAttribute method changes the context of the foreach loop. So here are two questions:

1. How can invoking the method screw up my foreach loop? Secondly, what's the most elegant workaround?
2. I realized I could loop through $item->attributes with yet another foreach method, then compare the attribute name to data-text and read the value in case of a match, but there surely has to be a better way to do so?!

Solution

The problem is the ul has text nodes as children along with the lis textnodes do not have attribute therefore you get an error. just test if the child is an element node before you try to access its attribute

foreach ($items as $item) {
         if ($item->nodeType == XML_ELEMENT_NODE)
         echo $item->getAttribute('data-text');
}

You can also use getElementsByTagName(), although if you have nested lists the lis in them will also be selected.

$items = $list->getElementsByTagName('li');
foreach ($items as $item) {
    echo $item->getAttribute('data-text');
}

Comments

[clausvdb]

Ah, there we go. It all makes sence now. Since the lists are indeed nested, comparing the nodeType seems the perfect way to go. Thanks a million!

[Avatar]

If you var_dump the nodeType you will get integers, check out the int values at php.net/manual/en/dom.constants.php