如何使用<x/>而非<x>来反序列化一个空的XML元素</x>

Question

我有一个XSD架构和用于在运行时构建组件的XML文件。这些对象可以具有自定义设置。在XSD文件，这被定义为：

<xs:complexType name="ComponentSettings"> 
    <xs:sequence> 
    <xs:any minOccurs="0"/> 
    </xs:sequence> 
</xs:complexType> 

，并在XSD实例化为：

<xs:complexType name="Component"> 
    <xs:sequence> 
    <xs:element name="Version" type="VersionRecord"/> 
    <xs:element name="Settings" type="ComponentSettings"/> 
    </xs:sequence> 
    <xs:attribute name="Name" type="xs:string" use="required"/> 
</xs:complexType> 

反序列化XML文件时，我邂逅了一个有趣的问题。如果我有一个没有设置的组件，并且XML看起来像这样：

<Settings></Settings> 

我没有问题。

然而，如果在XML看起来是这样的：

<Settings/> 

然后反序列化将失败默默跟随这个标记和我结束了一个不完整的记录。

我使用xsd2code产生下面的代码：

<System.CodeDom.Compiler.GeneratedCodeAttribute("System.Xml", "4.0.30319.18060"), _ 
System.SerializableAttribute(), _ 
System.ComponentModel.DesignerCategoryAttribute("code"), _ 
System.Xml.Serialization.XmlRootAttribute([Namespace]:="", IsNullable:=True)> _ 
Partial Public Class Component 
    Implements System.ComponentModel.INotifyPropertyChanged 

    Private versionField As VersionRecord 

    Private settingsField As System.Xml.XmlElement 

    Private nameField As String 

    Private Shared sSerializer As System.Xml.Serialization.XmlSerializer 

    '''<summary> 
    '''Component class constructor 
    '''</summary> 
    Public Sub New() 
     MyBase.New() 
     Me.versionField = New VersionRecord() 
    End Sub 

    <System.Xml.Serialization.XmlElementAttribute(Order:=0)> _ 
    Public Property Version() As VersionRecord 
     Get 
      Return Me.versionField 
     End Get 
     Set(value As VersionRecord) 
      If (Not (Me.versionField) Is Nothing) Then 
       If (versionField.Equals(value) <> True) Then 
        Me.versionField = value 
        Me.OnPropertyChanged("Version") 
       End If 
      Else 
       Me.versionField = value 
       Me.OnPropertyChanged("Version") 
      End If 
     End Set 
    End Property 

    <System.Xml.Serialization.XmlElementAttribute(Order:=2)> _ 
    Public Property Settings() As System.Xml.XmlElement 
     Get 
      Return Me.settingsField 
     End Get 
     Set(value As System.Xml.XmlElement) 
      If (Not (Me.settingsField) Is Nothing) Then 
       If (settingsField.Equals(value) <> True) Then 
        Me.settingsField = value 
        Me.OnPropertyChanged("Settings") 
       End If 
      Else 
       Me.settingsField = value 
       Me.OnPropertyChanged("Settings") 
      End If 
     End Set 
    End Property 

    <System.Xml.Serialization.XmlAttributeAttribute()> _ 
    Public Property Name() As String 
     Get 
      Return Me.nameField 
     End Get 
     Set(value As String) 
      If (Not (Me.nameField) Is Nothing) Then 
       If (nameField.Equals(value) <> True) Then 
        Me.nameField = value 
        Me.OnPropertyChanged("Name") 
       End If 
      Else 
       Me.nameField = value 
       Me.OnPropertyChanged("Name") 
      End If 
     End Set 
    End Property 

#Region "Serialize/Deserialize" 
    '''<summary> 
    '''Serializes current Component object into an XML document 
    '''</summary> 
    '''<returns>string XML value</returns> 
    Public Overridable Overloads Function Serialize(ByVal encoding As System.Text.Encoding) As String 
     Dim streamReader As System.IO.StreamReader = Nothing 
     Dim memoryStream As System.IO.MemoryStream = Nothing 
     Try 
      memoryStream = New System.IO.MemoryStream() 
      Dim xmlWriterSettings As System.Xml.XmlWriterSettings = New System.Xml.XmlWriterSettings() 
      xmlWriterSettings.Encoding = encoding 
      Dim xmlWriter As System.Xml.XmlWriter = xmlWriter.Create(memoryStream, xmlWriterSettings) 
      Serializer.Serialize(xmlWriter, Me) 
      memoryStream.Seek(0, System.IO.SeekOrigin.Begin) 
      streamReader = New System.IO.StreamReader(memoryStream) 
      Return streamReader.ReadToEnd 
     Finally 
      If (Not (streamReader) Is Nothing) Then 
       streamReader.Dispose() 
      End If 
      If (Not (memoryStream) Is Nothing) Then 
       memoryStream.Dispose() 
      End If 
     End Try 
    End Function 

    Public Overridable Overloads Function Serialize() As String 
     Return Serialize(Encoding.UTF8) 
    End Function 

    '''<summary> 
    '''Deserializes workflow markup into an Component object 
    '''</summary> 
    '''<param name="xml">string workflow markup to deserialize</param> 
    '''<param name="obj">Output Component object</param> 
    '''<param name="exception">output Exception value if deserialize failed</param> 
    '''<returns>true if this XmlSerializer can deserialize the object; otherwise, false</returns> 
    Public Overloads Shared Function Deserialize(ByVal xml As String, ByRef obj As Component, ByRef exception As System.Exception) As Boolean 
     exception = Nothing 
     obj = CType(Nothing, Component) 
     Try 
      obj = Deserialize(xml) 
      Return True 
     Catch ex As System.Exception 
      exception = ex 
      Return False 
     End Try 
    End Function 

    Public Overloads Shared Function Deserialize(ByVal xml As String, ByRef obj As Component) As Boolean 
     Dim exception As System.Exception = Nothing 
     Return Deserialize(xml, obj, exception) 
    End Function 

    Public Overloads Shared Function Deserialize(ByVal xml As String) As Component 
     Dim stringReader As System.IO.StringReader = Nothing 
     Try 
      stringReader = New System.IO.StringReader(xml) 
      Return CType(Serializer.Deserialize(System.Xml.XmlReader.Create(stringReader)), Component) 
     Finally 
      If (Not (stringReader) Is Nothing) Then 
       stringReader.Dispose() 
      End If 
     End Try 
    End Function 

    '''<summary> 
    '''Serializes current Component object into file 
    '''</summary> 
    '''<param name="fileName">full path of outupt xml file</param> 
    '''<param name="exception">output Exception value if failed</param> 
    '''<returns>true if can serialize and save into file; otherwise, false</returns> 
    Public Overridable Overloads Function SaveToFile(ByVal fileName As String, ByVal encoding As System.Text.Encoding, ByRef exception As System.Exception) As Boolean 
     exception = Nothing 
     Try 
      SaveToFile(fileName, encoding) 
      Return True 
     Catch e As System.Exception 
      exception = e 
      Return False 
     End Try 
    End Function 

    Public Overridable Overloads Function SaveToFile(ByVal fileName As String, ByRef exception As System.Exception) As Boolean 
     Return SaveToFile(fileName, Encoding.UTF8, exception) 
    End Function 

    Public Overridable Overloads Sub SaveToFile(ByVal fileName As String) 
     SaveToFile(fileName, Encoding.UTF8) 
    End Sub 

    Public Overridable Overloads Sub SaveToFile(ByVal fileName As String, ByVal encoding As System.Text.Encoding) 
     Dim streamWriter As System.IO.StreamWriter = Nothing 
     Try 
      Dim xmlString As String = Serialize(encoding) 
      streamWriter = New System.IO.StreamWriter(fileName, False, encoding.UTF8) 
      streamWriter.WriteLine(xmlString) 
      streamWriter.Close() 
     Finally 
      If (Not (streamWriter) Is Nothing) Then 
       streamWriter.Dispose() 
      End If 
     End Try 
    End Sub 

    '''<summary> 
    '''Deserializes xml markup from file into an Component object 
    '''</summary> 
    '''<param name="fileName">string xml file to load and deserialize</param> 
    '''<param name="obj">Output Component object</param> 
    '''<param name="exception">output Exception value if deserialize failed</param> 
    '''<returns>true if this XmlSerializer can deserialize the object; otherwise, false</returns> 
    Public Overloads Shared Function LoadFromFile(ByVal fileName As String, ByVal encoding As System.Text.Encoding, ByRef obj As Component, ByRef exception As System.Exception) As Boolean 
     exception = Nothing 
     obj = CType(Nothing, Component) 
     Try 
      obj = LoadFromFile(fileName, encoding) 
      Return True 
     Catch ex As System.Exception 
      exception = ex 
      Return False 
     End Try 
    End Function 

    Public Overloads Shared Function LoadFromFile(ByVal fileName As String, ByRef obj As Component, ByRef exception As System.Exception) As Boolean 
     Return LoadFromFile(fileName, Encoding.UTF8, obj, exception) 
    End Function 

    Public Overloads Shared Function LoadFromFile(ByVal fileName As String, ByRef obj As Component) As Boolean 
     Dim exception As System.Exception = Nothing 
     Return LoadFromFile(fileName, obj, exception) 
    End Function 

    Public Overloads Shared Function LoadFromFile(ByVal fileName As String) As Component 
     Return LoadFromFile(fileName, Encoding.UTF8) 
    End Function 

    Public Overloads Shared Function LoadFromFile(ByVal fileName As String, ByVal encoding As System.Text.Encoding) As Component 
     Dim file As System.IO.FileStream = Nothing 
     Dim sr As System.IO.StreamReader = Nothing 
     Try 
      file = New System.IO.FileStream(fileName, FileMode.Open, FileAccess.Read) 
      sr = New System.IO.StreamReader(file, encoding) 
      Dim xmlString As String = sr.ReadToEnd 
      sr.Close() 
      file.Close() 
      Return Deserialize(xmlString) 
     Finally 
      If (Not (file) Is Nothing) Then 
       file.Dispose() 
      End If 
      If (Not (sr) Is Nothing) Then 
       sr.Dispose() 
      End If 
     End Try 
    End Function 
#End Region 

#Region "Clone method" 
    '''<summary> 
    '''Create a clone of this Component object 
    '''</summary> 
    Public Overridable Function Clone() As Component 
     Return CType(Me.MemberwiseClone, Component) 
    End Function 
#End Region 
End Class 

我很好奇为什么发生这种情况，以及是否有办法不遇到此。

Answer 1

根据http://msdn.microsoft.com/en-us/library/system.xml.xmlreader.isemptyelement%28v=vs.110%29.aspx，“不会为空元素生成相应的EndElement节点。”

看来，微软有意识地对待这两种情况，公然无视XML标准。

我创建了下面的方法来修补XML文本：

 Public Function XMLReaderPatch(rawXML As String) As String 
      If String.IsNullOrEmpty(rawXML) Then Return rawXML 

      'Pattern for finding items similar to <name*/> where * may represent whitespace followed by text and/or whitespace 
      Dim pattern As String = "<(\S+)(\s[^<|>]*)?/>" 
      'Pattern for replacing with items similar to <name*></name> where * may represent whitespace followed by text and/or whitespace 
      Dim replacement As String = "<$1$2></$1>" 
      Dim rgx As New Text.RegularExpressions.Regex(pattern) 

      Return rgx.Replace(rawXML, replacement) 
     End Function 

Answer 2

<设置> </Settings>和< Settings />在语义上在XML中是相同的。如果您的代码对另一个的响应不同，则代码已损坏。