DOMXPath::evaluate()

(PHP 5 >= 5.1.0, PHP 7)

Evaluates the given XPath expression and returns a typed result if possible

说明

publicDOMXPath::evaluate(string $expression[,DOMNode$contextnode[,bool $registerNodeNS= TRUE]]): mixed

Executes the given XPath$expressionand returns a typed result if possible.

参数

$expression

The XPath expression to execute.

$contextnode

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

$registerNodeNS

The optional$registerNodeNScan 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$expressionis malformed or the$contextnodeis invalid,DOMXPath::evaluate() returns FALSE.

更新日志

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

• DOMXPath::query() Evaluates the given XPath expression

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])".

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.

this class can substitute the method evaluate while it is not validated. Made for Yuri Bastos and Joo Gilberto Magalhes. 
<?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
      }
    }
  }
?>

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'));
?>