xpath - 获取与 XPath 表达式匹配的 XML 节点

Question

我希望你能帮忙解决这个问题。我在网上尝试了一些 XPath 测试仪，但未能找到解决方案。

我正在尝试从此 XML 中获取具有“~tid”属性的第一个节点的值:

<Response status="ok" version="1.1">
                 <Action>
                    <Page>
                       <Params>
                          <Param name="~tid" value="1345811517165"/>
                          <Param name="~action-type" value="DATA"/>
                          <Param name="~from-page" value="login"/>
                          <Param name="~from-act" value="submitData"/>
                          <Param name="login_USERNAME" value="" type="0"/>
                          <Param name="login_PASSWORD" value="" type="0"/>
                       </Params>
                    </Page>
                    <Data name="clientData" method="POST">
                       <Params>
                          <Param name="timezoneoffset" value=""/>
                          <Param name="daylightsavings" value=""/>
                       </Params>
                    </Data>
                 </Action>
                 <Action>
                    <Page>
                       <Params>
                          <Param name="~tid" value="1345811517165"/>
                          <Param name="~action-type" value="NAV"/>
                          <Param name="~from-page" value="login"/>
                          <Param name="~from-act" value="resetPassword"/>
                          <Param name="~to-page" value="login_resetPassword"/>
                       </Params>
                    </Page>
                 </Action>
                 <Action>
                    <Page>
                       <Params>
                          <Param name="~tid" value="1345811517165"/>
                          <Param name="~action-type" value="NAV"/>
                          <Param name="~from-page" value="login"/>
                          <Param name="~from-act" value="newUser"/>
                          <Param name="~to-page" value="login_newUser"/>
                       </Params>
                    </Page>
                 </Action>
</Response>

我使用的 XPath 是:

//Params[1]/Param[@name='~tid']/@value

它获取所有三个值。我怎样才能得到第一个？

Answer 1

尝试

/descendant::Params[1]/Param[@name='~tid']/@value

来自W3C XPath specification :

NOTE: The location path //para[1] does not mean the same as the location path /descendant::para[1]. The latter selects the first descendant para element; the former selects all descendant para elements that are the first para children of their parents.