用xpath选择一个css类 [英] Selecting a css class with xpath

问题描述

我只想自己选择一个类叫做.date

出于某种原因，我无法使其工作。如果有人知道我的代码有什么问题，那将非常感谢。

  @ $ doc = new DOMDocument（）; 
 @ $ doc-> loadHTML（$ html）; 
 $ xml = simplexml_import_dom（$ doc）; //只是为了使xpath更简单
 $ images = $ xml-> xpath（'// [@ class =date]'）; 
 foreach（$ images为$ img）
 {
 echo $ img。; 
 
  

解决方案

我想写规范回答这个问题，因为上面的答案有问题。

我们的问题

CSS 选择器：

  .foo 
  

会选择任何具有 foo 类的元素。

你如何在XPath中做到这一点？

虽然XPath比CSS更强大，但XPath并没有本地等价的CSS类选择器。然而，有一个解决方案。

正确的做法

XPath 是：

// * [contains（concat（，normalize函数

=https://www.w3.org/TR/1999/REC-xpath-19991116/ =nofollow noreferrer>规范化空间去除前导和尾随空白（并且还替换了空白字符序列由一个单一的空间）。

（从更一般的意义上说）这也是CSS选择器的等价物：

  * [class〜=foo] 
  

，它将匹配其 class 属性值为空格分隔值列表的任何元素，其中一个元素与 foo 完全相同。 p>

一些明显但错误的做法

XPath选择器：

  // * [@ class =foo] 
  

不起作用！因为它不会匹配具有多个类的元素，例如

 < div class =foo bar> 
  

如果类名周围有任何额外的空格，它也不会匹配：

 < div class =foo> 
  

'改进'XPath选择器

  // * [contains（@class，foo）] 
  

也不起作用！因为它错误地将元素与类 foobar 匹配，例如
$ b

  < div class =foobar>信用转到这个家伙，谁是这个问题的最早发布的解决方案，我发现在网络上：
  http://dubinko.info/blog/2007/10/01/simple-parsing-of-space-seprated-attributes-in-xpathxslt/  
 
I want to select just a class on its own called .date

For some reason, I cannot get this to work. If anyone knows what is wrong with my code, it would be much appreciated.
@$doc = new DOMDocument();
@$doc->loadHTML($html);
$xml = simplexml_import_dom($doc); // just to make xpath more simple
$images = $xml->xpath('//[@class="date"]');                             
foreach ($images as $img)
{
    echo  $img." ";
}

解决方案
I want to write the canonical answer to this question because the answer above has a problem.

Our problem

The CSS selector:
.foo
will select any element that has the class foo.

How do you do this in XPath?

Although XPath is more powerful than CSS, XPath doesn't have a native equivalent of a CSS class selector.  However, there is a solution.

The right way to do it

The equivalent selector in XPath is:
//*[contains(concat(" ", normalize-space(@class), " "), " foo ")]
The function normalize-space strips leading and trailing whitespace (and also replaces sequences of whitespace characters by a single space).

(In a more general sense) this is also the equivalent of the CSS selector:
*[class~="foo"]
which will match any element whose class attribute value is a list of whitespace-separated values, one of which is exactly equal to foo.

A couple of obvious, but wrong ways to do it

The XPath selector:
//*[@class="foo"]
doesn't work!  because it won't match an element that has more than one class, for example
<div class="foo bar">
It also won't match if there is any extra whitespace around the class name:
<div class="  foo ">
The 'improved' XPath selector
//*[contains(@class, "foo")]
doesn't work either! because it wrongly matches elements with the class foobar, for example
<div class="foobar">
Credit goes to this fella, who was the earliest published solution to this problem that I found on the web:
http://dubinko.info/blog/2007/10/01/simple-parsing-of-space-seprated-attributes-in-xpathxslt/ 

                        
这篇关于用xpath选择一个css类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！