VB.net XML 按标签名称删除每隔一个元素

Question

我正在使用以下 XML 示例：

<order>
    <name></name>
    <etc></etc>
    <etc></etc>
    <components>
        <component>
            <sub></sub>
        </component>
        <component>
            <sub></sub>
        </component>
        <component>
            <sub></sub>
        </component>
        <component>
            <sub></sub>
        </component>
    </components>
</order>

我正在尝试选择并删除每一秒 <component>，它是 vb.net 中的 subs。

以下是我目前得到的：

'make xmldocument object to hold xml string'
Dim XMLDoc As New XMLDocument()
XMLDoc.LoadXML(strXMLContent)
'get all elements named component'
Dim componentList As XmlNodeList = XMLDoc.GetElementsByTagName("Component")
Dim c As Integer
Dim i As Integer = 1
'for every component element add i to itself to only get seconds'
'and if on a second element, remove it and all sub elements inside it'
For c = 0 To componentList.Count - 1
    i += i
    If i > 2 Then
        componentList(c).ParentNode.RemoveChild(componentList(c))
    End If
Next c
'output to a string to see results'
x &= XMLDoc.DocumentElement.OuterXml

我遇到的问题是，当我运行此程序时，在调用实际 RemoveChild() 的行上得到“Object reference not set to an instance of an object”。

Answer 1

我的问题在于两件事，我如何添加我的 i 整数，以及 if 语句结构，当组合时，我删除的 componentList(c) 确实为空。以下是我的工作修复。

'make xmldocument object to hold xml string'
 Dim XMLDoc As New XMLDocument()
 XMLDoc.LoadXML(strXMLContent)
'get all elements named component'
 Dim componentList As XmlNodeList = XMLDoc.GetElementsByTagName("Component")
 Dim c As Integer
 Dim i As Integer = 0
'for every "Component" element add 1 to i - remove every second by checking if i is modular'
 For c = 0 To componentList.Count - 1
     i += 1
     If Not i Mod 2 Then
         componentList(c).ParentNode.RemoveChild(componentList(c))
     End If
 Next c
'output to a string to see results'
 x &= XMLDoc.DocumentElement.OuterXml

Answer 2

试试这个：

Private Function GetRidOfEveryOtherComponent(ByVal strXML As String) As String
    'make xmldocument object to hold xml string'
    Dim XMLDoc As New XmlDocument()
    XMLDoc.LoadXml(strXML)
    'get every other component item
    Dim componentList As XmlNodeList = XMLDoc.SelectNodes("order/components/component[position() mod 2 = 1]")
    For c As Integer = 0 To componentList.Count - 1
        componentList(c).ParentNode.RemoveChild(componentList(c))
    Next c
    'output to a string to see results'
    Return XMLDoc.DocumentElement.OuterXml
End Function

这个很酷的 mod 功能是由 Paul 提供的，这里：Selecting every other node uing XPATH