XPath在VBA中返回字符串或布尔值?

可以使用XSL转换计算XPath表达式,特别是 xsl:value-of .

我写了一篇 Evaluate 在这个原则上起作用的函数。它在内存中创建一个XSL样式表,其中包含一个XSL模板,该模板将接受一个XPath表达式,对其求值,并返回一个新的XML文档,该文档包含 <result> 节点。它会检查以确保 value-of Long , Double Boolean ,或 String .

books.xml 链接到的MSDN页中的文件(必须将路径更改为 books.xml文件 如果你想运行这些测试)。

Public Sub Test_Evaluate()

    Dim doc As New DOMDocument
    Dim value As Variant

    doc.async = False
    doc.Load "C:\Development\StackOverflow\XPath Evaluation\books.xml"

    Debug.Assert (doc.parseError.errorCode = 0)

    ' Sum of book prices should be a Double and equal to 30.97
    '
    value = Evaluate(doc, "sum(descendant::price)")
    Debug.Assert TypeName(value) = "Double"
    Debug.Assert value = 30.97

    ' Title of second book using text() selector should be "The Confidence Man"
    '
    value = Evaluate(doc, "descendant::book[2]/title/text()")
    Debug.Assert TypeName(value) = "String"
    Debug.Assert value = "The Confidence Man"

    ' Title of second book using string() function should be "The Confidence Man"
    '
    value = Evaluate(doc, "string(/bookstore/book[2]/title)")
    Debug.Assert TypeName(value) = "String"
    Debug.Assert value = "The Confidence Man"

    ' Total number of books should be 3
    '
    value = Evaluate(doc, "count(descendant::book)")
    Debug.Assert TypeName(value) = "Long"
    Debug.Assert value = 3

    ' Title of first book should not be "The Great Gatsby"
    '
    value = Evaluate(doc, "not(string(/bookstore/book[1]/title))='The Great Gatsby'")
    Debug.Assert TypeName(value) = "Boolean"
    Debug.Assert value = False

    ' Genre of second book should be "novel"
    '
    value = Evaluate(doc, "string(/bookstore/book[2]/attribute::genre)='novel'")
    Debug.Assert TypeName(value) = "Boolean"
    Debug.Assert value = True

    ' Selecting a non-existent node should generate an error
    '
    On Error Resume Next

    value = Evaluate(doc, "string(/bookstore/paperback[1])")
    Debug.Assert Err.Number = vbObjectError

    On Error GoTo 0

End Sub

这里是 评价 IsLong 函数是帮助函数,使数据类型转换代码更具可读性):

注: 作为 barrowc DOMDocument 具有特定于版本的类名,例如 DOMDocument30 (MSXML3)或 DOMDocument60

看问题 Which version of MSXML should I use? 有关MSXML不同版本的详细信息。

Public Function Evaluate(ByVal doc As DOMDocument, ByVal xpath As String) As Variant

    Static styleDoc As DOMDocument
    Dim valueOf As IXMLDOMElement
    Dim resultDoc As DOMDocument
    Dim result As Variant

    If styleDoc Is Nothing Then

        Set styleDoc = New DOMDocument

        styleDoc.loadXML _
            "<xsl:stylesheet version='1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform'>" & _
                "<xsl:template match='/'>" & _
                    "<result>" & _
                        "<xsl:value-of />" & _
                    "</result>" & _
                "</xsl:template>" & _
            "</xsl:stylesheet>"

    End If

    Set valueOf = styleDoc.selectSingleNode("//xsl:value-of")
    valueOf.setAttribute "select", xpath

    Set resultDoc = New DOMDocument
    doc.transformNodeToObject styleDoc, resultDoc

    If resultDoc.documentElement.childNodes.length = 0 Then
        Err.Raise vbObjectError, , "Expression '" & xpath & "' returned no results."
    End If

    result = resultDoc.documentElement.Text

    If IsLong(result) Then
        result = CLng(result)
    ElseIf IsNumeric(result) Then
        result = CDbl(result)
    ElseIf result = "true" Or result = "false" Then
        result = CBool(result)
    End If

    Evaluate = result

End Function

Private Function IsLong(ByVal value As Variant) As Boolean

    Dim temp As Long

    If Not IsNumeric(value) Then
        Exit Function
    End If

    On Error Resume Next

    temp = CLng(value)

    If Not Err.Number Then
        IsLong = (temp = CDbl(value))
    End If

End Function