DOMXPath::evaluate

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

DOMXPath::evaluate — Evaluates the given XPath expression and returns a typed result if possible

说明

public DOMXPath::evaluate ( string $expression , DOMNode|null $contextNode = null , bool $registerNodeNS = true ) : mixed

Executes the given XPath expression and returns a typed result if possible.

参数

expression

The XPath expression to execute.

contextNode

The optional contextNode can be specified for doing relative XPath queries. By default, the queries are relative to the root element.

registerNodeNS

The optional registerNodeNS can be specified to disable automatic registration of the context node.

返回值

Returns a typed result if possible or a DOMNodeList containing all nodes matching the given XPath expression.

If the expression is malformed or the contextNode is invalid, DOMXPath::evaluate() returns false.

范例

Example #1 Getting the count of all the english books

<?php

$doc = new DOMDocument;

$doc->load('book.xml');

$xpath = new DOMXPath($doc);

$tbody = $doc->getElementsByTagName('tbody')->item(0);

// our query is relative to the tbody node
$query = 'count(row/entry[. = "en"])';

$entries = $xpath->evaluate($query, $tbody);
echo "There are $entries english books\n";

?>

以上例程会输出：

There are 2 english books

参见

User Contributed Notes

danny at webdevelopers dot eu 28-Jan-2020 11:36
The only way how to distinguish FALSE returned value from syntax error FALSE is to re-run the XPath expression wrapped in string() function. If must return empty string. If it returns FALSE again then it is an error.

<?php

        $ret=$this->xp->evaluate($eval, $context);

        // Error detection: DOMXPath::evaluate() returns FALSE on error
        // so does DOMXPath::evaluate("boolean(/nothing)")
        // @workaround webdevelopers.eu
        if ($ret === false && $this->xp->evaluate("string($eval)", $context) === false) {
            throw new Exception("Invalid XPath expression ".json_encode($eval), 3491);
        }
?>
aazaharov81 at gmail dot com 14-Jan-2015 12:48
To query DOMNodes by their HTML classes, use such snippet
<?php

// CssClassXPathSelector
function ccxs($class) {
    return '[contains(concat(" ", normalize-space(@class), " "), " ' . $class . ' ")]';
}

 // then just
 $domitems = $this->xpath("//*[@id='searchResultsRows']//a" . ccxs('listing_row'));
?>
daniel at danielnorton dot com 25-Jun-2011 09:56
Note that this method does not provide any means to distinguish between a successful result that returns FALSE and an error.

For example, this will succeed and return FALSE:

<?php $xpath->evaluate("1 = 0"); ?>

One workaround when you know you are expecting a Boolean is to wrap the result with string(). e.g.

<?php $xpath->evaluate("string(1 = 0)"); ?>

This will return a string "false" on success, or the Boolean FALSE on error.
Damien Bezborodov 28-Mar-2011 06:13
If your expression returns a node set, you will get a DOMNodeList instead of a typed result. Instead, try modifying your expression from "//node[1]" to "string(//node[1])".
yuriucsal at NOSPAM dot yahoo dot com dot br 06-Mar-2005 12:55
this class can substitute the method evaluate while it is not validated. Made for Yuri Bastos and Jo?o Gilberto Magalh?es.

<?php

    class XPtahQuery
    {
        // function returns a DOMNodeList from a relative xPath
        public static function selectNodes($pNode, $xPath)
        {

            $pos = strpos(self::getFullXpath($pNode),"/",1);
            $xPathQuery = substr(self::getFullXpath($pNode),$pos);//to paste  /#document[1]/
            $xPathQueryFull = $xPathQuery. $xPath;
            $domXPath = new DOMXPath($pNode->ownerDocument);
            $rNodeList = $domXPath->query($xPathQueryFull);

                return $rNodeList;
        }
        // function returns a DOMNode from a xPath from other DOMNode
        public static function selectSingleNode($pNode, $xPath)
        {

            $pos = strpos(self::getFullXpath($pNode),"/",1);
            $xPathQuery = substr(self::getFullXpath($pNode),$pos);//to paste  /#document[1]/
            $xPathQueryFull = $xPathQuery. $xPath;
            $domXPath = new DOMXPath($pNode->ownerDocument);
            $rNode = $domXPath->query($xPathQueryFull)->item(0);

                return $rNode;
        }
        //utilitaries functions off selectSingleNode
        private function getNodePos($pNode, $nodeName)
        {
            if($pNode == null)
                {
                        return 0;
            }
            else
            {
                $var = 0;
                    if ($pNode->previousSibling != null)
                    {
                    if ($pNode->previousSibling->nodeName == $nodeName)
                    {
                        $var = 1;
                    }
                    }
                    return self::getNodePos($pNode->previousSibling, $nodeName) + $var;
            }
        }
        //utilitaries functions off selectSingleNode
        private function getFullXpath($pNode)
        {
            if($pNode == null)
                {
                        return "";
            }
            else
            {

                return self::getFullXpath($pNode->parentNode) . "/" . $pNode->nodeName . "[" .strval(self::getNodePos($pNode, $pNode->nodeName)+1) . "]";//+1 to get the real xPath index

            }
        }
    }
?>