VB.Net XMLTextWriter无法访问文件，因为该文件正在使用中？

我正在编写一个自动更新函数，从XML读取客户端版本，然后在修补一些文件后，XMLTextWriter应该更新客户端版本，但每当我尝试创建TextWriter时，我都会被告知，即使我关闭了读卡器，该文件仍在使用中。我错过了什么

  'pulling in reader from xml'

  Dim clientReader As XmlReader = XmlReader.Create("launch.xml")

    'Read the XML files to determine the server version'

    clientReader.ReadToFollowing("serverURL")
    Dim serverURL As String = clientReader.ReadElementContentAsString()
    Dim serverXMLpath As String = serverURL & "Updater/serverInfo.xml"
    Dim serverReader As XmlTextReader = New XmlTextReader(serverXMLpath)
    serverReader.ReadToFollowing("serverVer")
    Dim serverVer As Double = serverReader.ReadElementContentAsDouble()

    'Read client XML to determine clientVersion'
    clientReader.ReadToFollowing("clientVer")
    Dim clientVer As Double = clientReader.ReadElementContentAsDouble()

    'Determine what updates need to be downloaded'

    serverReader.ReadToFollowing("totalUpdates")
    Dim totalUpdates As Integer = serverReader.ReadElementContentAsInt()

    '.....'
    'files are downloaded and updated here'
    '.....'


    clientReader.Close()
    serverReader.Close()


    'change the client version!'
    Dim clientWriter As New XmlTextWriter("launch.xml", System.Text.Encoding.UTF8)
    'clientWriter.WriteElementString("clientVer", serverVer)

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try设置可能重复为nothing:clientReader=nothing服务器阅读器=nothing@jdweng我试了一下。另一个进程仍在使用该文件。两个对象都有ReadState（）。确定读取状态：Closed、EndOfFile、Error、Initial、Interactive。我检查了ReadState，它在关闭前列为Interactive，在使用Close（）时列为Closed。当读卡器设置为Nothing时，我得到一个NullReferenceException