DOMDocument::getElementById

(PHP 5, PHP 7)

DOMDocument::getElementById — Searches for an element with a certain id

说明

public DOMElement DOMDocument::getElementById ( string $elementId )

This function is similar to DOMDocument::getElementsByTagName but searches for an element with a given id.

For this function to work, you will need either to set some ID attributes with DOMElement::setIdAttribute or a DTD which defines an attribute to be of type ID. In the later case, you will need to validate your document with DOMDocument::validate or DOMDocument::$validateOnParse before using this function.

参数

elementId: The unique id value for an element.

返回值

Returns the DOMElement or NULL if the element is not found.

范例

Example #1 DOMDocument::getElementById() Example

以下范例使用了 book.xml，其内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books [
  <!ELEMENT books   (book+)>
  <!ELEMENT book    (title, author+, xhtml:blurb?)>
  <!ELEMENT title   (#PCDATA)>
  <!ELEMENT blurb   (#PCDATA)>
  <!ELEMENT author  (#PCDATA)>
  <!ATTLIST books   xmlns        CDATA  #IMPLIED>
  <!ATTLIST books   xmlns:xhtml  CDATA  #IMPLIED>
  <!ATTLIST book    id           ID     #IMPLIED>
  <!ATTLIST author  email        CDATA  #IMPLIED>
]>
<?xml-stylesheet type="text/xsl" href="style.xsl"?>
<books xmlns="http://books.php/" xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <book id="php-basics">
    <title>PHP Basics</title>
    <author email="jim.smith@basics.php">Jim Smith</author>
    <author email="jane.smith@basics.php">Jane Smith</author>
    <xhtml:blurb><![CDATA[
<p><em>PHP Basics</em> provides an introduction to PHP.</p>
]]></xhtml:blurb>
  </book>
  <book id="php-advanced">
    <title>PHP Advanced Programming</title>
    <author email="jon.doe@advanced.php">Jon Doe</author>
  </book>
</books>

  <?php

$doc  = new  DomDocument ;

 // We need to validate our document before refering to the id
 $doc -> validateOnParse  =  true ;
 $doc -> Load ( 'book.xml' );

echo  "The element whose id is 'php-basics' is: "  .  $doc -> getElementById ( 'php-basics' )-> tagName  .  "\n" ;

 ?>

以上例程会输出：

The element whose id is 'php-basics' is: book

参见

DOMDocument::getElementsByTagName() - Searches for all elements with given local tag name

用户评论:

[#1] ed at edgiardina dot com [2010-10-13 11:41:03]

Please note that if your HTML does not contain a doctype declaration, then getElementById will always return null.

[#2] paradox_haze at live dot de [2010-03-02 10:53:02]

Had some issues with getElementById() while searching for a specific element in a XHTML document.
I wrote a small function what was solving my problem:

<?php function getElementById($id) { $xpath = new DOMXPath($this->domDocument); return $xpath->query("/ $xmlDom = new DOMDocument('1.0', 'utf-8'); $xmlDom->formatOutput = true; // we want a nice output // create a root $eltRoot = $xmlDom->createElement("root"); $xmlDom->appendChild($eltRoot); $eltChild = $xmlDom->createElement("child"); $eltRoot->appendChild($eltChild); // add a id attribute $attr = $xmlDom->createAttribute("xml:id"); // needs xml prefix or getElementById won't work $eltChild->appendChild($attr); /// create the text node and append to the created element $tNode = $xmlDom->createTextNode("id_8120528"); $attr->appendChild($tNode); $eltChild->setIdAttribute("xml:id", true); // VERY IMPORT or getElementById won't work // add a id attribute $attr = $xmlDom->createAttribute("status"); $eltChild->appendChild($attr); /// create the text node and append to the created element $tNode = $xmlDom->createTextNode("partial"); $attr->appendChild($tNode); // add a subchild $eltSub = $xmlDom->createElement("sub_child"); $eltChild->appendChild($eltSub); $tNode = $xmlDom->createTextNode("Some Data"); $eltSub->appendChild($tNode); $id = null; $id = $xmlDom->getElementById("id_8120528"); assert ($id != null); $strId = $id->getAttribute("xml:id"); // bug? empty $strStatus = $id->getAttribute("status"); // this works! assert ($id !=null); $xmlDom->save("./_data/test.xml"); $xmlDom->load("./_data/test.xml"); // reloading fixes the problem $nodeRoot = $xmlDom->getElementsByTagName("root"); if ($nodeRoot->length > 0) { $eltRoot = $nodeRoot->item(0); } assert($eltRoot != null); $id = null; $id = $xmlDom->getElementById("id_8120528"); assert ($id != null); $strId = $id->getAttribute("xml:id"); // this works now! $strStatus = $id->getAttribute("status"); // this works! ?>

[#4] guillaume dot crico at gmail dot com [2008-10-01 07:55:35]

You don't want to use "xml:id" ?
Here is the relaxNG trick (with a generic schema):
(tested with libxml 2.6.26)

<?php $doc = new DOMDocument(); $doc->load(...); $rng = ' <grammar xmlns="http://relaxng.org/ns/structure/1.0" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">     <start>         <element>             <anyName/>             <ref name="anythingID"/>         </element>     </start>     <define name="anythingID">         <zeroOrMore>             <choice>                 <element>                     <anyName/>                     <ref name="anythingID"/>                 </element>                 <attribute name="id">                     <data type="ID"/>                 </attribute>                 <zeroOrMore>                     <attribute><anyName/></attribute>                 </zeroOrMore>                 <text/>             </choice>         </zeroOrMore>     </define> </grammar> '; $doc->relaxNGValidateSource($rng); var_dump($doc->getElementById('id1')); ?>

Note that ID values must be valid ones :
  - integers do no work!
  - @see http://www.w3.org/TR/REC-xml/#id
  - => (Letter | '_' | ':') ( Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender  )*

[#5] simon at somewhere dot com [2007-01-29 20:07:06]

SAVE YOURSELF A MAJOR HEADACHE AND A LOT OF SEARCHING THROUGH DOCUMENTATION -

Instead of using $object->setAttribute('id', 'id_name_here')
USE THIS: $object->setAttribute('xml:id', 'id_name_here')

Then, to get the node value: $domDocumentObject->getElementById('id_name_here');

The xml:id attribute should AUTOMATICALLY be defined!!

Woohoo! That was easy......

[#6] jonbarnett at gmail dot com [2006-11-01 08:36:35]

If your XML document does not have a DTD that defines the "id" attribute as an ID, then the easiest thing to do is to use XPath->query() to find an element that matches "//[@id='x']"

[#7] Tangui dot Le-Pense at laposte dot net [2006-04-08 06:00:36]

Validating a document from a DTD so as to use getElementById is sometimes impossible (for example when the head and body elements are not included yet in a XHtml document : the validation failed).
Fortunately, xml:id is supported by this function :)
That may be useful.
http://www.w3.org/TR/xml-id/

[#8] [2005-12-20 07:04:59]

If you're trying to use getElementById with a xml file validated on a xsd file you must first use the schemaValidate function or getElementById will return null
Example:

  $dom = new DomDocument();
  $dom->load("users.xml");
  $dom->schemaValidate("users.xsd");

  $curruser = $dom->getElementById($user->name);

[#9] bart at mediawave dot nl [2005-09-11 04:46:24]

It seems getElementById works fine without setting validateOnParse to true. Which is nice since setting this to true caused some performance problems with my script.