Question

我有以下XPath表达式：

//a[@attribute='my-attribute']

当我在XPath搜索的HTML中具有以下元素时，它会按预期匹配：

<a attribute="my-attribute">Some text</a>

但是，如果该元素下有一个<svg>标记，则XPath不返回匹配项：

<a attribute="my-attribute">
    <svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%"
        viewBox="0 0 24 24" focusable="false"></svg>
</a>

为什么在这种情况下XPath不匹配？有什么方法可以修改表达式以使其匹配？

编辑：

显然，它与<svg>元素上的名称空间有关。使用local-name()函数使其与我使用的XPath测试器相匹配：

//*[local-name()='a' and @attribute='my-attribute']

但是，当通过Selenium WebDriver运行时，这仍然不匹配。关于如何与Selenium一起工作的任何想法吗？

Answer 1

您可能会对XPath托管环境如何呈现选定的a元素感到困惑。

在svg元素中添加a元素将不影响

//a[@attribute='my-attribute']

对于

<a attribute="my-attribute">Some text</a>

a元素的字符串值不仅包含空格字符，而且包含

<a attribute="my-attribute">
    <svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%"
        viewBox="0 0 24 24" focusable="false"></svg>
</a>

a元素的字符串值仅包含空格，因此对于所选文本结果，您将看不到任何选定内容。

如果您评估count(//a[@attribute='my-attribute'])，则两种情况下的结果都可能相同。

Answer 2

以下是vb.net中可能的解决方案。

Public Class XmlNodeListWithNamespace
    ' see https://stackoverflow.com/questions/55385520/xpath-doesnt-match-when-desired-element-contains-child-elements
    ' @JaSON I would have thought the same thing,
    ' but removing the xmlns attribute from the svg tag
    ' causes the //a[@attribute='my-attribute'] expression to match.
    ' – Andrew Mairose
    ' Mar 28 at 13:07 "Asked 5 months ago  Active 5 months ago" implies 2019-03-28 13:07.

    ' Therefore, I first considered deleting all occurrences of
    '       xmlns="" and xmlns="http://www.w3.org/1999/xhtml"
    ' I did this using the following Replacement.
    ' gstrHtml = Regex.Replace(
    '            input:=gstrHtml,
    '            pattern:=" *xmlns=""[^""]*""",
    '            replacement:="",
    '            options:=RegexOptions.IgnoreCase
    '        )

    ' However, the solution below retains the namespace, while avoiding unsightly xpath strings.

    ''' <summary>
    ''' For a given xpath, returns an XmlNodeList, taking account of the xmlns namespace.
    ''' </summary>
    ''' <param name="oXmlDocument">The current XML document.</param>
    ''' <param name="xpath">A normal xpath string, without any namespace qualifier.</param>
    ''' <returns>The XmlNodeList for the given xpath.</returns>
    Public Shared Function NodeList(
        oXmlDocument As XmlDocument,
        xpath As String
    ) As XmlNodeList

        Dim strXpath As String = xpath

        ' Insert Namespace Qualifier.  For example, 
        '    "//pre"                                            becomes "//x:pre"
        '    "/html/body/form/div/pre"                          becomes "/x:html/x:body/x:form/x:div/x:pre"
        '    "//div[@id='nv_bot_contents']/pre"                 becomes "//x:div[@id='nv_bot_contents']/x:pre"
        '    "//div[@id='nv_bot_contents']/pre[@data-xxx='X2']" becomes "//x:div[@id='nv_bot_contents']/x:pre[@data-xxx='X2']"
        '    "//div[@id='nv_bot_contents']/pre[@data-xxx]"      becomes "//x:div[@id='nv_bot_contents']/x:pre[@data-xxx]"
        '    "//pre[@data-xxx]"                                 becomes "//x:pre[@data-xxx]"
        strXpath = Regex.Replace(
                        input:=strXpath,
                        pattern:="(/)(\w+)",
                        replacement:="$1x:$2"
                    )

        ' See https://stackoverflow.com/questions/40796231/how-does-xpath-deal-with-xml-namespaces/40796315#40796315
        Dim oXmlNamespaceManager As New XmlNamespaceManager(nameTable:=oXmlDocument.NameTable)
        oXmlNamespaceManager.AddNamespace("x", "http://www.w3.org/1999/xhtml")

        Dim oXmlNodeList As XmlNodeList = oXmlDocument.SelectNodes(
            xpath:=strXpath,
            nsmgr:=oXmlNamespaceManager
        )

        Return oXmlNodeList

    End Function

End Class

示例调用：

Dim oXmlNodeList As XmlNodeList =
            XmlNodeListWithNamespace.NodeList(
                oXmlDocument:=oXmlDocument,
                xpath:="//pre"
            )

当所需元素包含子元素时，XPath不匹配吗？

2 个答案: