php 中的 DOMNode 到 DOMElement

Question

I want to convert a DOMNode object from a call to getElementsByTagName() to a DOMElement in order to access methods like getElementsByTagName() on the child element. In any other language, I would cast and it would be easy, but after some quick looking, PHP does not have object casting. So what I need to know is how to get a DOMElement object from a DOMNode object.

Answer 1

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

This is what I use in my project to minimize IDE warning.

/**
 * Cast a DOMNode into a DOMElement
 */
    function cast_e(DOMNode $node) : DOMElement {
    if ($node) {
        if ($node->nodeType === XML_ELEMENT_NODE) {
            return $node;
        }
    }
    return null;
}

Answer 3

You don't need to do any explicit typecasting, just check if your DOMNode object has a nodeType of XML_ELEMENT_NODE .

PHP will be perfectly happy with this.

If you use PHPLint to check your code you will notice that PHPLint complains about using getElementsByTagName on a DOMNode object. To get around this you need to jump through the following hoop:

/*.object.*/ $obj = $node;
$element = /*.(DOMElement).*/ $obj;

Then you will have a $element variable of the correct type and no complaints from PHPLint.

Answer 4

I know this is mostly an annoying IDE problem.

The reason is $DOMNodeList->item(0) witch returns a DOMNode ( or at least the IDE thinks so ).

To fix this you will have to Extract out the $DOMDocument->getElementsByTagName( $tagName )->item($index) into a method of its own. In the DOCBlock you set the @return statement to DOMElement witch fixes the inspection problem.

This Works at least in PHPStorm.

Answer 5

If anyone is looking for a more elegant solution in IntelliJ/PHPStorm . I managed to solve the issue like this:

    private function doSomething(DOMNode $child){
        
        if(!$child instanceof DOMElement)
            throw new Exception('DOMElement expected but got something else.');
        
        $attr = $child->getAttribute('attr'); //recognized by PHPStorm now as DOMElement
        
        /* and more code */
        
    }

All my code corretly assumes DOMNode which is de super class of DOMElement but also DOMComment etc. When I need DOMElement to use getAttribute for example, then I add above check.