Mikel
[转载]XPath语法 在C#中使用XPath示例 – 玉开 – 博客园.
XPath可以快速定位到Xml中的节点或者属性。XPath语法很简单，但是强大够用，它也是使用xslt的基础知识。
示例Xml：
<span class="com"><!--?xml version="1.0" encoding="utf-8" ?--></span><span class="pln">100 this is a black cat80 this is a white cat80 this is a yellow cat100 this is a black dog80 this is a white dog80 this is a yellow dog</span> |
XPath的语法：
1. XPath中的符号
|
符号 |
说明 |
示例 |
示例说明 |
|
/ |
表示从根节点开始选择 |
/pets |
选择根节点pets |
|
表示节点和子节点之间的间隔符 |
/pets/dog |
选择pets节点下的dog节点 |
|
|
//xx |
表示从整个xml文档中查找，而不考虑当前节点位置 |
//price |
选择文档中所有的price节点 |
|
. |
单个英文半角句点表示选择当前节点 |
/pets/. |
选择pets节点 |
|
.. |
双点，表示选择父节点 |
/pets/dog[0]/.. |
表示pets节点，也就是第一个dog节点的父节点 |
|
@xx |
表示选择属性 |
//dog/@color |
表示选择所有dog节点的color属性集合 |
|
[…] |
中括号表示选择条件，括号内为条件 |
//dog[@color=’white’] |
所有color为white的dog节点 |
|
//dog[/price<100] |
所有price字节点值小于100的dog节点 |
||
|
中括号内数字为节点索引，类似C#等语言中的数组,数组下标是从1开始的 |
//dog[1] |
第1个dog节点 |
|
|
//dog[last()] |
最后一个dog节点，last()是xPath内置函数 |
||
|
| |
单竖杠表示合并节点结合 |
//dog[@color=’white’] | //cat[@color=’white’] |
color属性为white的dog节点和color属性为white的cat节点 |
|
* |
星号表示任何名字的节点或者属性 |
//dog/* |
表示dog节点的所有子节点 |
|
//dog/@* |
表示dog节点的所有属性节点 |
2. XPath数学运算符
+ 加号表示加
– 表示数字相减
* 表示乘以
div 表示除以，这里数学上的除号/已经被用作节点之间分隔符了
mod 表示取余
3. XPath逻辑运算符
= 等于，相当于C#中的 ==
!= 不等于
> 大于
>= 大于等于
< 小于
<= 小于等于
and 并且 与关系
or 或者 或关系
4. XPath Axes 从字面翻译这个是XPath轴的意思，但根据我的理解这个翻译成XPath节点关系运算关键字更合适，就是一组关键字加上::双冒号表示和当前节点有关系的一个或者一组节点.
使用语法： axisname::nodetest[predicate] 即轴名字::节点名字[取节点条件]
具体说明如下：
|
关键字 |
说明 |
示例 |
示例说明 |
|
ancestor |
当前节点的父祖节点 |
ancestor::pig |
当前节点的祖先节点中的pig节点 |
|
ancestor-or-self |
当前节点以及其父祖节点 |
ancestor::pig |
|
|
attribute |
当前节点的所有属性 |
attribute::weight |
相当于@weight，attribute::和@是等价的 |
|
child |
当前节点的所有字节点 |
child::*[name()!=’price’] |
选择名字不是price的子节点 |
|
descendant |
子孙节点 |
descendant::*[@*] |
有属性的子孙节点 |
|
descendant-or-self |
子孙节点以及当前节点 |
descendant-or-self::* |
|
|
following |
Xml文档中当前节点之后的所有节点 |
following::* |
|
|
following-sibling |
当前节点的同父弟弟节点 |
following-sibling:: |
|
|
preceding |
Xml文档中当前节点之前的所有节点 |
preceding::* |
|
|
namespace |
选取当前节点的所有命名空间节点 |
namespace::* |
|
|
parent |
当前节点的父节点 |
parent:: |
相当于双点.. |
|
preceding-sibling |
当前节点之后的同父兄节点 |
preceding-sibling::* |
|
|
self |
当前节点 |
self::* |
相当于单点. |
5. 常用的XPath函数介绍：
在XPath表达式中常用的函数有下面两个：
position() 表示节点的序号例如 //cat[position() = 2] 表示取序号为2的dog节点
last() 表示取最后一个节点 //cat[last()]
name() 表示当前节点名字 /pets/*[name() != ‘pig’] 表示/pets下名字不是pig的子节点
XPath的函数还有很多，包括字符串函数，数字函数和时间函数等，具体可以参考w3的网站。
以上是XPath的语法，下面我们看下如何在.Net中使用XPath
在.Net中可以通过XPathDocument或者XmlDocument类使用XPath。XPathDocument是只读的方式定位Xml节点或者属性文本等，而XmlDocument则是可读写的。
如下代码示例展示了如何使用XPathDocument和XmlDocument。
<span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Collections</span><span class="pun">.</span><span class="typ">Generic</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Linq</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Text</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Xml</span><span class="pun">.</span><span class="typ">XPath</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Xml</span><span class="pun">;</span><span class="pln"></span><span class="kwd">namespace</span><span class="pln"> </span><span class="typ">UseXPathDotNet</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Program</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">Main</span><span class="pun">(</span><span class="kwd">string</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="typ">UseXPathWithXPathDocument</span><span class="pun">();</span><span class="pln"></span><span class="typ">UseXPathWithXmlDocument</span><span class="pun">();</span><span class="pln"></span><span class="typ">Console</span><span class="pun">.</span><span class="typ">Read</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">UseXPathWithXmlDocument</span><span class="pun">()</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="typ">XmlDocument</span><span class="pln"> doc </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">XmlDocument</span><span class="pun">();</span><span class="pln">doc</span><span class="pun">.</span><span class="typ">Load</span><span class="pun">(</span><span class="str">"http://www.cnblogs.com/yukaizhao/rss"</span><span class="pun">);</span><span class="pln"></span><span class="com">//使用xPath选择需要的节点</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> nodes </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"/rss/channel/item[position()<=10]"</span><span class="pun">);</span><span class="pln"></span><span class="kwd">foreach</span><span class="pln"> </span><span class="pun">(</span><span class="typ">XmlNode</span><span class="pln"> item </span><span class="kwd">in</span><span class="pln"> nodes</span><span class="pun">)</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="kwd">string</span><span class="pln"> title </span><span class="pun">=</span><span class="pln"> item</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"title"</span><span class="pun">).</span><span class="typ">InnerText</span><span class="pun">;</span><span class="pln"></span><span class="kwd">string</span><span class="pln"> url </span><span class="pun">=</span><span class="pln"> item</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"link"</span><span class="pun">).</span><span class="typ">InnerText</span><span class="pun">;</span><span class="pln"></span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="str">"{0} = {1}"</span><span class="pun">,</span><span class="pln"> title</span><span class="pun">,</span><span class="pln"> url</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">UseXPathWithXPathDocument</span><span class="pun">()</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="typ">XPathDocument</span><span class="pln"> doc </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">XPathDocument</span><span class="pun">(</span><span class="str">"http://www.cnblogs.com/yukaizhao/rss"</span><span class="pun">);</span><span class="pln"></span><span class="typ">XPathNavigator</span><span class="pln"> xPathNav </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">CreateNavigator</span><span class="pun">();</span><span class="pln"></span><span class="com">//使用xPath取rss中最新的10条随笔</span><span class="pln"></span><span class="typ">XPathNodeIterator</span><span class="pln"> nodeIterator </span><span class="pun">=</span><span class="pln"> xPathNav</span><span class="pun">.</span><span class="typ">Select</span><span class="pun">(</span><span class="str">"/rss/channel/item[position()<=10]"</span><span class="pun">);</span><span class="pln"></span><span class="kwd">while</span><span class="pln"> </span><span class="pun">(</span><span class="pln">nodeIterator</span><span class="pun">.</span><span class="typ">MoveNext</span><span class="pun">())</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="typ">XPathNavigator</span><span class="pln"> itemNav </span><span class="pun">=</span><span class="pln"> nodeIterator</span><span class="pun">.</span><span class="typ">Current</span><span class="pun">;</span><span class="pln"></span><span class="kwd">string</span><span class="pln"> title </span><span class="pun">=</span><span class="pln"> itemNav</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"title"</span><span class="pun">).</span><span class="typ">Value</span><span class="pun">;</span><span class="pln"></span><span class="kwd">string</span><span class="pln"> url </span><span class="pun">=</span><span class="pln"> itemNav</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"link"</span><span class="pun">).</span><span class="typ">Value</span><span class="pun">;</span><span class="pln"></span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="str">"{0} = {1}"</span><span class="pun">,</span><span class="pln">title</span><span class="pun">,</span><span class="pln">url</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
XPath使用示例，请看下面的代码注释
<span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Collections</span><span class="pun">.</span><span class="typ">Generic</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Linq</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Text</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="pln">IO</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="typ">Xml</span><span class="pun">;</span><span class="pln"></span><span class="kwd">namespace</span><span class="pln"> </span><span class="typ">UseXPath1</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Program</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">Main</span><span class="pun">(</span><span class="kwd">string</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="kwd">string</span><span class="pln"> xml </span><span class="pun">=</span><span class="pln"> </span><span class="pun">@</span><span class="str">"<!--?xml version=""1.0"" encoding=""utf-8"" ?-->100 this is a black cat80 this is a white cat110 this is a yellow cat114 this is a black dog80 this is a white dog80 this is a yellow dog8000 this is a white pig"</span><span class="pun">;</span><span class="pln"></span><span class="kwd">using</span><span class="pln"> </span><span class="pun">(</span><span class="typ">StringReader</span><span class="pln"> rdr </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">StringReader</span><span class="pun">(</span><span class="pln">xml</span><span class="pun">))</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="typ">XmlDocument</span><span class="pln"> doc </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">XmlDocument</span><span class="pun">();</span><span class="pln">doc</span><span class="pun">.</span><span class="typ">Load</span><span class="pun">(</span><span class="pln">rdr</span><span class="pun">);</span><span class="pln"></span><span class="com">//取所有pets节点下的dog字节点</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> nodeListAllDog </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"/pets/dog"</span><span class="pun">);</span><span class="pln"></span><span class="com">//所有的price节点</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> allPriceNodes </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"//price"</span><span class="pun">);</span><span class="pln"></span><span class="com">//取最后一个price节点</span><span class="pln"></span><span class="typ">XmlNode</span><span class="pln"> lastPriceNode </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"//price[last()]"</span><span class="pun">);</span><span class="pln"></span><span class="com">//用双点号取price节点的父节点</span><span class="pln"></span><span class="typ">XmlNode</span><span class="pln"> lastPriceParentNode </span><span class="pun">=</span><span class="pln"> lastPriceNode</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">".."</span><span class="pun">);</span><span class="pln"></span><span class="com">//选择weight*count=40的所有动物，使用通配符*</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> nodeList </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"/pets/*[@weight*@count=40]"</span><span class="pun">);</span><span class="pln"></span><span class="com">//选择除了pig之外的所有动物,使用name()函数返回节点名字</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> animalsExceptPigNodes </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"/pets/*[name() != 'pig']"</span><span class="pun">);</span><span class="pln"></span><span class="com">//选择价格大于100而不是pig的动物</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> priceGreaterThan100s </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"/pets/*[price div @weight >10 and name() != 'pig']"</span><span class="pun">);</span><span class="pln"></span><span class="kwd">foreach</span><span class="pln"> </span><span class="pun">(</span><span class="typ">XmlNode</span><span class="pln"> item </span><span class="kwd">in</span><span class="pln"> priceGreaterThan100s</span><span class="pun">)</span><span class="pln"></span><span class="pun">{</span><span class="pln"></span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="pln">item</span><span class="pun">.</span><span class="typ">OuterXml</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="com">//选择第二个dog节点</span><span class="pln"></span><span class="typ">XmlNode</span><span class="pln"> theSecondDogNode </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"//dog[position() = 2]"</span><span class="pun">);</span><span class="pln"></span><span class="com">//使用xpath ，axes 的 parent 取父节点</span><span class="pln"></span><span class="typ">XmlNode</span><span class="pln"> parentNode </span><span class="pun">=</span><span class="pln"> theSecondDogNode</span><span class="pun">.</span><span class="typ">SelectSingleNode</span><span class="pun">(</span><span class="str">"parent::*"</span><span class="pun">);</span><span class="pln"></span><span class="com">//使用xPath选择第二个dog节点前面的所有dog节点</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> dogPresibling </span><span class="pun">=</span><span class="pln"> theSecondDogNode</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"preceding::dog"</span><span class="pun">);</span><span class="pln"></span><span class="com">//取文档的所有子孙节点price</span><span class="pln"></span><span class="typ">XmlNodeList</span><span class="pln"> childrenNodes </span><span class="pun">=</span><span class="pln"> doc</span><span class="pun">.</span><span class="typ">SelectNodes</span><span class="pun">(</span><span class="str">"descendant::price"</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="typ">Console</span><span class="pun">.</span><span class="typ">Read</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
C#处理Xml的相关随笔：
7.通过Xslt转化Xml格式
请尊重作者的劳动，转载请保留链接 玉开的技术博客
