Question

我有一个类似

的XML文件

<?xml version="1.0">
<playlist>
     <name>My Playlist</name>
     <song>
         <name>Song Name Here</name>
         <path>Path to song here</path>
         <note>Song notes here</note>
         <artist>Song artist here</artist>
         <type>Song type here</type>
     </song>
     <song>
         <name>Song Name Here</name>
         <path>Path to song here</path>
         <note>Song notes here</note>
         <artist>Song artist here</artist>
         <type>Song type here</type>
     </song>
</playlist>

我正在尝试从xml文件中删除歌曲节点，但我无法弄清楚我得到的错误的原因。我还在学习视觉基础知识。

错误：对象引用未设置为对象的实例。

这是我的代码

    Private Sub MsItemRemoveClick(sender As System.Object, e As EventArgs) Handles msItemRemove.Click

        If lvwPlaylist.SelectedItems.Count > 0 Then

            Dim xmlDoc As New XmlDocument

            xmlDoc.Load(_playlistpath & lblPlaylistName.Text & ".xml")

            Dim songs As XmlElement = xmlDoc.SelectSingleNode("song")

            For Each item As ListViewItem In lvwPlaylist.SelectedItems

                For Each node As XmlElement In songs

                    If node.SelectSingleNode("name").InnerText = item.SubItems(0).Text Then

                        MsgBox(node.SelectSingleNode("name").InnerText) '<------ this is where the error pops up on 'node.ParentNode.RemoveAll()

                    End If

                Next

                item.Remove()

            Next

            xmlDoc.Save(_playlistpath & lblPlaylistName.Text & ".xml")

        End If

    End Sub

我的努力是遍历所有选定的列表视图项目，如果歌曲的名称与songs node中的歌曲名称相匹配，则删除name的父节点

Answer 1

为清晰起见，删除了ListView ....

对于此XML文件......

<?xml version="1.0"?>
<playlist>
     <name>My Playlist</name>
     <song>
         <name>Alpha song</name>
         <path>Path to song here</path>
         <note>Song notes here</note>
         <artist>Song artist here</artist>
         <type>Song type here</type>
     </song>
     <song>
         <name>Beta song</name>
         <path>Path to song here</path>
         <note>Song notes here</note>
         <artist>Song artist here</artist>
         <type>Song type here</type>
     </song>
     <song>
         <name>Charlie song</name>
         <path>Path to song here</path>
         <note>Song notes here</note>
         <artist>Song artist here</artist>
         <type>Song type here</type>
     </song>
     <song>
         <name>Delta song</name>
         <path>Path to song here</path>
         <note>Song notes here</note>
         <artist>Song artist here</artist>
         <type>Song type here</type>
     </song>
</playlist>

以C：\ Junk \ Junk1.xml保存在磁盘上，此代码将查找并删除两个中间节点......

Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
  Dim strFilenameIn As String = "C:\Junk\Junk1.xml"
  Dim strFilenameOut As String = "C:\Junk\Junk2.xml"

  Dim lstNames As New List(Of String)
  lstNames.Add("Beta song")
  lstNames.Add("Charlie song")

  Dim xmlDoc As New XmlDocument
  xmlDoc.Load(strFilenameIn)
  For Each strSongName As String In lstNames
    Dim xnl As XmlNodeList = xmlDoc.SelectNodes("/playlist/song/name")
    For i As Integer = xnl.Count - 1 To 0 Step -1
      Dim xnd As XmlNode = xnl(i)
      If xnd.FirstChild.Value = strSongName Then 'match'
        xmlDoc.DocumentElement.RemoveChild(xnd.ParentNode)
      End If
    Next
  Next strSongName
  xmlDoc.Save(strFilenameOut)
  MsgBox("Finished")
End Sub

从xml文件中删除节点会引发一个对象引用错误

1 个答案: