PHP HTML DomDocument getElementById 问题
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PHP HTML DomDocument getElementById problems
提问by Jé Queue
A little new to PHP parsing here, but I can't seem to get PHP's DomDocument to return what is clearly an identifiable node. The HTML loaded will come from the 'net so can't necessarily guarantee XML compliance, but I try the following:
这里对 PHP 解析有点新，但我似乎无法让 PHP 的 DomDocument 返回明显可识别的节点。加载的 HTML 将来自“网络”，因此不一定保证符合 XML，但我尝试以下操作：
<?php
header("Content-Type: text/plain");
$html = '<html><body>Hello <b id="bid">World</b>.</body></html>';
$dom = new DomDocument;
$dom->preserveWhiteSpace = false;
$dom->validateOnParse = true;
/*** load the html into the object ***/
$dom->loadHTML($html);
var_dump($dom);
$belement = $dom->getElementById("bid");
var_dump($belement);
?>
Though I receive no error, I only receive the following as output:
虽然我没有收到任何错误，但我只收到以下输出：
object(DOMDocument)#1 (0) {
}
NULL
Should I not be able to look up the <b>tag as it does indeed have an id?
我是否应该无法查找<b>标签，因为它确实有一个 id？
回答by Wrikken
The Manualexplains why:
手册解释了原因：
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.
要使此函数工作，您需要使用 DOMElement->setIdAttribute() 或 DTD 设置一些 ID 属性，该 DTD 将属性定义为 ID 类型。在后一种情况下，在使用此函数之前，您需要使用 DOMDocument->validate() 或 DOMDocument->validateOnParse 验证您的文档。
By all means, go for valid HTML & provide a DTD.
无论如何，选择有效的 HTML 并提供 DTD。
Quick fixes:
快速修复：
- Call
$dom->validate();and put up with the errors (or fix them), afterwards you can use$dom->getElementById(), regardless of the errors for some reason. - Use XPath if you don't feel like validing:
$x = new DOMXPath($dom); $el = $x->query("//*[@id='bid']")->item(0); - Come to think of it: if you just set
validateOnParseto true beforeloading the HTML, if would also work ;P
- 调用
$dom->validate();并忍受错误（或修复它们），之后您可以使用$dom->getElementById()，无论出于某种原因的错误如何。 - 如果您不想验证，请使用 XPath：
$x = new DOMXPath($dom); $el = $x->query("//*[@id='bid']")->item(0); - 想想看：如果你在加载 HTML之前设置
validateOnParse为 true ，如果也可以工作;P
.
.
$dom = new DOMDocument();
$html ='<html>
<body>Hello <b id="bid">World</b>.</body>
</html>';
$dom->validateOnParse = true; //<!-- this first
$dom->loadHTML($html); //'cause 'load' == 'parse
$dom->preserveWhiteSpace = false;
$belement = $dom->getElementById("bid");
echo $belement->nodeValue;
Outputs 'World' here.
在此处输出“世界”。
回答by Martin Vseticka
Well, you should check if $dom->loadHTML($html);returns true (success) and I would try
好吧，你应该检查是否$dom->loadHTML($html);返回 true（成功），我会尝试
var_dump($belement->nodeValue);
for output to get a clue what might be wrong.
输出以获得可能出错的线索。
EDIT:http://www.php-editors.com/php_manual/function.domdocument-get-element-by-id.html- it seems that DomDocument uses XPath internally.
编辑：http://www.php-editors.com/php_manual/function.domdocument-get-element-by-id.html - DomDocument 似乎在内部使用 XPath。
Example:
例子：
$xpath = xpath_new_context($dom);
var_dump(xpath_eval_expression($xpath, "//*[@ID = 'YOURIDGOESHERE']"));
