NSXMLDocument,带有命名空间的nodesForXPath

Question

我想从xml文件中获取一组元素,但是一旦元素涉及名称空间,它就会失败.

这是xml文件的一个片段:

<gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
     version="1.0" creator="Groundspeak Pocket Query"
     xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd http://www.groundspeak.com/cache/1/0 http://www.groundspeak.com/cache/1/0/cache.xsd" 
     xmlns="http://www.topografix.com/GPX/1/0"> 
  <name>My Finds Pocket Query</name>   
  <desc>Geocache file generated by Groundspeak</desc>   
  <author>Groundspeak</author>   
  <email>contact@groundspeak.com</email> 
  <time>2010-09-15T16:18:55.9846906Z</time> 
  <keywords>cache, geocache, groundspeak</keywords>   
  <bounds minlat="41.89687" minlon="5.561883" maxlat="70.669967" maxlon="25.74735" />    
  <wpt lat="62.244933" lon="25.74735">
    <time>2010-01-11T08:00:00Z</time>
    <name>GC22W1T</name>
    <desc>Kadonneet ja karanneet by ooti, Traditional Cache (1.5/2)</desc>
    <url>http://www.geocaching.com/seek/cache_details.aspx?guid=4af28fe9-401b-44df-b058-5fd5399fc083</url>
    <urlname>Kadonneet ja karanneet</urlname>
    <sym>Geocache Found</sym>
    <type>Geocache|Traditional Cache</type>
    <groundspeak:cache id="1521507" available="True" archived="False" xmlns:groundspeak="http://www.groundspeak.com/cache/1/0">
      <groundspeak:name>Kadonneet ja karanneet</groundspeak:name>
      <groundspeak:placed_by>ooti</groundspeak:placed_by>
      <groundspeak:owner id="816431">ooti</groundspeak:owner>
      <groundspeak:type>Traditional Cache</groundspeak:type>
      <groundspeak:container>Small</groundspeak:container>
      <groundspeak:difficulty>1.5</groundspeak:difficulty>
      <groundspeak:terrain>2</groundspeak:terrain>
      <groundspeak:country>Finland</groundspeak:country>
      <groundspeak:state>
      </groundspeak:state>
      <groundspeak:short_description html="True">
      </groundspeak:short_description>
      <groundspeak:encoded_hints>
      </groundspeak:encoded_hints>
      <groundspeak:travelbugs />
    </groundspeak:cache>   
  </wpt>
</gpx>

我想得到所有的grounspeak:cache元素,但似乎既没有//groundspeak:cache也没有//cache返回任何东西.

NSArray *caches = [self.xml nodesForXPath:@"//cache" error:&error];

任何线索？

编辑:有没有基于可可的软件,我可以加载我的xml并测试不同的xpaths？我对objective-c和cocoa很陌生,所以检查它确实是我的xpath是错误的将是很好的..

Answer 1

这//cache意味着:没有命名空间(或空命名空间)下的后代元素

您的groundspeak:cache元素位于名称空间URI下http://www.groundspeak.com/cache/1/0.

所以,如果你不能声明一个名称空间前缀绑定(我认为你不能用cocoa ...),你可以使用这个XPath表达式:

//*[namespace-uri()='http://www.groundspeak.com/cache/1/0' and
    local-name()='cache']

如果你不想对命名空间这么严格......

//*[local-name()='cache']

但这最后是一个不好的做法,因为你最终可能会选择错误的节点,因为在处理XML时,你的工具应该支持命名空间.

作为证明,这个样式表:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
            <xsl:copy-of select="//*[namespace-uri() =
                                     'http://www.groundspeak.com/cache/1/0' and
                                     local-name() = 'cache']"/>
    </xsl:template>
</xsl:stylesheet>

输出:

<groundspeak:cache id="1521507" available="True" archived="False"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            xmlns="http://www.topografix.com/GPX/1/0"
            xmlns:groundspeak="http://www.groundspeak.com/cache/1/0">
    <groundspeak:name>Kadonneet ja karanneet</groundspeak:name>
    <groundspeak:placed_by>ooti</groundspeak:placed_by>
    <groundspeak:owner id="816431">ooti</groundspeak:owner>
    <groundspeak:type>Traditional Cache</groundspeak:type>
    <groundspeak:container>Small</groundspeak:container>
    <groundspeak:difficulty>1.5</groundspeak:difficulty>
    <groundspeak:terrain>2</groundspeak:terrain>
    <groundspeak:country>Finland</groundspeak:country>
    <groundspeak:state></groundspeak:state>
    <groundspeak:short_description html="True"></groundspeak:short_description>
    <groundspeak:encoded_hints></groundspeak:encoded_hints>
    <groundspeak:travelbugs />
</groundspeak:cache>