按其同级查找XML元素

如何使用Visual Basic查找XML元素的同级？假设我有：

<Data>
  <Mail>
    <Subject>Welcome!</Subject>
    <From>Antonios</From>
    <Content>Welcome! How can I assist you?</Content>
  </Mail>
  <Mail>
    <Subject>Test!</Subject>
    <From>John</From>
    <Content>Hello Friend!</Content>
  </Mail>
</Data>

欢迎
安东尼奥斯
欢迎我能帮你什么忙？
测试！
约翰
你好，朋友！

现在我有一个列表框，可以添加每个主题，所以列表显示：欢迎！和测试！ 现在我想知道，当我点击“欢迎！”时，一个文本框显示“欢迎！”元素的内容，另一个文本框显示“欢迎”元素的“内容”。

---

换句话说，我正在寻找一个特定元素的兄弟

您可以通过多种方式来实现这一点。以下是如何使用

XmlDocument

和XPath实现此功能：

Dim doc As New XmlDocument()
Dim From As String = doc.SelectSingleNode("/Data/Mail[Subject='Welcome!']/From").InnerText
Dim Content As String = doc.SelectSingleNode("/Data/Mail[Subject='Welcome!']/Content").InnerText

显然，由于主题可能不是唯一的，所以最好使用唯一ID的元素，或者可以通过索引来实现。例如，这将从第一封邮件中选择：

Dim From As String = doc.SelectSingleNode("/Data/Mail[1]/From").InnerText

但是，这样做的最好方法是将所有需要的数据预先加载到内存中。除非数据量太大（听起来不像），否则这通常是最有意义的。因此，例如，我建议创建一个表示邮件消息的数据对象，例如：

Public Class Mail
    Public Property Subject() As String
        Get
            Return _subject
        End Get
        Set(ByVal value As String)
            _subject = value
        End Set
    End Property
    Private _subject As String

    Public Property From() As String
        Get
            Return _from
        End Get
        Set(ByVal value As String)
            _from = value
        End Set
    End Property
    Private _from As String

    Public Property Content() As String
        Get
            Return _content
        End Get
        Set(ByVal value As String)
            _content = value
        End Set
    End Property
    Private _content As String

    Public Overrides Function ToString() As String
        Return _subject
    End Function
End Class

Dim doc As New XmlDocument()
For Each node As XmlNode In doc.SelectNodes("/Data/Mail")
    Dim mail As New Mail()
    mail.Subject = node.SelectSingleNode("Subject").InnerText
    mail.From = node.SelectSingleNode("From").InnerText
    mail.Content = node.SelectSingleNode("Content").InnerText
    ListBox1.Items.Add(mail)
Next

Dim mail As Mail = CType(ListBox1.SelectedItem, Mail)
Label1.Text = mail.From
Label2.Text = mail.Content

然后，可以为XML中的每个邮件元素加载一个

Mail

对象。由于

ToString

方法被覆盖以显示主题，因此您可以直接将对象添加到列表框中，例如：

Public Class Mail
    Public Property Subject() As String
        Get
            Return _subject
        End Get
        Set(ByVal value As String)
            _subject = value
        End Set
    End Property
    Private _subject As String

    Public Property From() As String
        Get
            Return _from
        End Get
        Set(ByVal value As String)
            _from = value
        End Set
    End Property
    Private _from As String

    Public Property Content() As String
        Get
            Return _content
        End Get
        Set(ByVal value As String)
            _content = value
        End Set
    End Property
    Private _content As String

    Public Overrides Function ToString() As String
        Return _subject
    End Function
End Class

Dim doc As New XmlDocument()
For Each node As XmlNode In doc.SelectNodes("/Data/Mail")
    Dim mail As New Mail()
    mail.Subject = node.SelectSingleNode("Subject").InnerText
    mail.From = node.SelectSingleNode("From").InnerText
    mail.Content = node.SelectSingleNode("Content").InnerText
    ListBox1.Items.Add(mail)
Next

Dim mail As Mail = CType(ListBox1.SelectedItem, Mail)
Label1.Text = mail.From
Label2.Text = mail.Content

然后，当选择列表框中的项目时，您可以将所选项目强制转换为

邮件类型并访问其属性，例如：

Public Class Mail
    Public Property Subject() As String
        Get
            Return _subject
        End Get
        Set(ByVal value As String)
            _subject = value
        End Set
    End Property
    Private _subject As String

    Public Property From() As String
        Get
            Return _from
        End Get
        Set(ByVal value As String)
            _from = value
        End Set
    End Property
    Private _from As String

    Public Property Content() As String
        Get
            Return _content
        End Get
        Set(ByVal value As String)
            _content = value
        End Set
    End Property
    Private _content As String

    Public Overrides Function ToString() As String
        Return _subject
    End Function
End Class

Dim doc As New XmlDocument()
For Each node As XmlNode In doc.SelectNodes("/Data/Mail")
    Dim mail As New Mail()
    mail.Subject = node.SelectSingleNode("Subject").InnerText
    mail.From = node.SelectSingleNode("From").InnerText
    mail.Content = node.SelectSingleNode("Content").InnerText
    ListBox1.Items.Add(mail)
Next

Dim mail As Mail = CType(ListBox1.SelectedItem, Mail)
Label1.Text = mail.From
Label2.Text = mail.Content

但是，此时，如果数据不是太大，则更容易使用
XmlSerializer
将XML反序列化为对象，例如，首先创建一个定义整个XML文档的类，如下所示：

Public Class Data
    <XmlElement("Mail")> _
    Public Property Mails() As List(Of Mail)
        Get
            Return _mails
        End Get
        Set(ByVal value As List(Of Mail))
            _mails = value
        End Set
    End Property
    Private _mails As List(Of Mail)
End Class

Dim node As XmlNode = doc.SelectSingleNode("/Data/Mail[Subject='Welcome!']")
node.ParentNode.RemoveChild(node)

或者，如果您希望直接从XML文件中读取，而不是从字符串中反序列化它：

Dim serializer As New XmlSerializer(GetType(Data))
Using stream As New FileStream("Test.xml", FileMode.Open)
    Dim data As Data = CType(serializer.Deserialize(stream), Data)
    ListBox1.Items.AddRange(data.Mails.ToArray())
End Using

要回答您在下面的评论中提出的第二个问题，要删除给定的邮件，您可以这样做：

Public Class Data
    <XmlElement("Mail")> _
    Public Property Mails() As List(Of Mail)
        Get
            Return _mails
        End Get
        Set(ByVal value As List(Of Mail))
            _mails = value
        End Set
    End Property
    Private _mails As List(Of Mail)
End Class

Dim node As XmlNode = doc.SelectSingleNode("/Data/Mail[Subject='Welcome!']")
node.ParentNode.RemoveChild(node)

非常感谢。正是我要找的！你也知道（这样我就不必写新帖子了）我将如何删除某个有孩子的父母吗？@Antonios我更新了我的答案，也回答了你的第二个问题。不过，在将来，最好分别问每个问题。这对将来的其他人寻找同一问题的答案更有用，并且有助于你获得更多的声誉。