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XmlSerializer.UnknownElement Event

Occurs when the XmlSerializer encounters an XML element of unknown type during deserialization.

[Visual Basic]
Public Event UnknownElement As XmlElementEventHandler
[C#]
public event XmlElementEventHandler UnknownElement;
[C++]
public: __event XmlElementEventHandler* UnknownElement;

[JScript] In JScript, you can handle the events defined by a class, but you cannot define your own.

Event Data

The event handler receives an argument of type XmlElementEventArgs containing data related to this event. The following XmlElementEventArgs properties provide information specific to this event.

Property Description
Element Gets the object that represents the unknown XML element.
LineNumber Gets the line number where the unknown element was encountered if the XML reader is an XmlTextReader.
LinePosition Gets the place in the line where the unknown element occurs if the XML reader is an XmlTextReader.
ObjectBeingDeserialized Gets the object the XmlSerializer is deserializing.

Remarks

By default, after calling the Deserialize method, the XmlSerializer ignores XML attributes of unknown types. However, you can use this event to handle such node types.

Note   If the XmlAnyElementAttribute is applied to a field that returns an array of XmlElement objects, all unknown elements will be collected in the array. In that case, the UnknownElement event will not occur.

Example

[Visual Basic, C#, C++] The following example deserializes a class named Group that from a file named UnknownElements.xml. Whenever an element is found in the file that has no corresponding member in the class, the UnknownElement event occurs. To try the example, paste the XML code below into a file named UnknownElements.xml.

<?xml version="1.0" encoding="utf-8"?>
<Group xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <GroupName>MyGroup</GroupName>
  <GroupSize>Large</GroupSize>
  <GroupNumber>444</GroupNumber>
  <GroupBase>West</GroupBase>
</Group>
[Visual Basic] 
Imports System
Imports System.IO
Imports System.Xml.Serialization
Imports System.Xml
Imports System.Xml.Schema
Imports Microsoft.VisualBasic

Public Class Group
   Public GroupName As String 
End Class

Public Class Test
   Shared Sub Main()
      Dim t As Test = new Test()
      ' Deserialize the file containing unknown elements.
      t.DeserializeObject("UnknownElements.xml")
   End Sub

   Private Sub Serializer_UnknownElement _
   (sender As Object , e As XmlElementEventArgs)
      Console.WriteLine("Unknown Element")
      Console.WriteLine(ControlChars.Tab & e.Element.Name + " " & e.Element.InnerXml)
      Console.WriteLine(ControlChars.Tab & e.LineNumber & ":"  & e.LineNumber)
      Console.WriteLine(ControlChars.Tab & e.LinePosition & ":"   & e.LinePosition)
      
      Dim x As Group = CType( e.ObjectBeingDeserialized, Group)
      Console.WriteLine (x.GroupName)
      Console.WriteLine (sender.ToString())
   End Sub
   
   Private Sub DeserializeObject(filename As String)
      Dim ser As XmlSerializer = new XmlSerializer(GetType(Group))
      ' Add a delegate to handle unknown element events.
      AddHandler ser.UnknownElement, _
      AddressOf Serializer_UnknownElement 
      ' A FileStream is needed to read the XML document.
     Dim fs As FileStream  = new FileStream(filename, FileMode.Open)
     Dim g  As Group = CType(ser.Deserialize(fs),Group)
     fs.Close()
   End Sub
End Class

[C#] 
using System;
using System.IO;
using System.Xml.Serialization;
using System.Xml;
using System.Xml.Schema;

public class Group{
   public string GroupName;
}

public class Test{
   static void Main(){
      Test t = new Test();
      // Deserialize the file containing unknown elements.
      t.DeserializeObject("UnknownElements.xml");
   }
   private void Serializer_UnknownElement(object sender, XmlElementEventArgs e){
      Console.WriteLine("Unknown Element");
      Console.WriteLine("\t" + e.Element.Name + " " + e.Element.InnerXml);
      Console.WriteLine("\t LineNumber: " + e.LineNumber);
      Console.WriteLine("\t LinePosition: " + e.LinePosition);
      
      Group x  = (Group) e.ObjectBeingDeserialized;
      Console.WriteLine (x.GroupName);
      Console.WriteLine (sender.ToString());
   }
   private void DeserializeObject(string filename){
      XmlSerializer ser = new XmlSerializer(typeof(Group));
      // Add a delegate to handle unknown element events.
      ser.UnknownElement+=new XmlElementEventHandler(Serializer_UnknownElement);
      // A FileStream is needed to read the XML document.
     FileStream fs = new FileStream(filename, FileMode.Open);
     Group g = (Group) ser.Deserialize(fs);
     fs.Close();
       }
}

[C++] 
#using <mscorlib.dll>
#using <System.Xml.dll>
using namespace System;
using namespace System::IO;
using namespace System::Xml::Serialization;
using namespace System::Xml;
using namespace System::Xml::Schema;

__gc public class Group
{
public:
   String* GroupName;
};

__gc public class Test
{
public:
   void Serializer_UnknownElement(Object* sender, XmlElementEventArgs * e) 
   {
      Console::WriteLine(S"Unknown Element");
      Console::Write(S"\t {0}", e -> Element -> Name);
      Console::WriteLine(S" {0}", e -> Element -> InnerXml);
      Console::WriteLine(S"\t LineNumber: {0}", __box(e -> LineNumber));
      Console::WriteLine(S"\t LinePosition: {0}", __box(e -> LinePosition));

      Group *x  = dynamic_cast<Group*>(e -> ObjectBeingDeserialized);
      Console::WriteLine (x -> GroupName);
      Console::WriteLine (sender);
   }
   void DeserializeObject(String* filename)
   {
      XmlSerializer* ser = new XmlSerializer(__typeof(Group));
      // Add a delegate to handle unknown element events.
      ser -> UnknownElement += new XmlElementEventHandler(this, &Test::Serializer_UnknownElement);
      // A FileStream is needed to read the XML document.
      FileStream* fs = new FileStream(filename, FileMode::Open);
      Group *g = dynamic_cast<Group*>(ser -> Deserialize(fs));
      fs -> Close();
   }
};

int main()
{
   Test* t = new Test();
   // Deserialize the file containing unknown elements.
   t -> DeserializeObject(S"UnknownElements.xml");
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

XmlSerializer Class | XmlSerializer Members | System.Xml.Serialization Namespace | XmlAnyElementAttribute | UnknownNode | UnknownAttribute | Introducing XML Serialization | Controlling XML Serialization Using Attributes | Examples of XML Serialization | The XML Schema Definition Tool and XML Serialization

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