XmlAttributeOverrides Class
Assembly: System.Xml (in system.xml.dll)
The XmlAttributeOverrides enables the XmlSerializer to override the default way of serializing a set of objects. Overriding serialization in this way has two uses: first, you can control and augment the serialization of objects found in a DLL--even if you do not have access to the source; second, you can create one set of serializable classes, but serialize the objects in multiple ways. For example, instead of serializing members of a class instance as XML elements, you can serialize them as XML attributes, resulting in a more efficient document to transport.
After you create an XmlAttributeOverrides object, you pass it as an argument to the XmlSerializer constructor. The resulting XmlSerializer uses the data contained by the XmlAttributeOverrides to override attributes that control how objects are serialized. To accomplish this, the XmlAttributeOverrides contains a collection of the object types that are overridden, as well as an XmlAttributes object associated with each overridden object type. The XmlAttributes object itself contains an appropriate set of attribute objects that control how each field, property, or class is serialized.
The process for creating and using an XmlAttributeOverrides object is as follows:
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Create an XmlAttributes object.
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Create an attribute object that is appropriate to the object being overridden. For example, to override a field or property, create an XmlElementAttribute, using the new, derived type. You can optionally assign a new ElementName, or Namespace that overrides the base class's attribute name or namespace.
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Add the attribute object to the appropriate XmlAttributes property or collection. For example, you would add the XmlElementAttribute to the XmlElements collection of the XmlAttributes object, specifying the member name that is being overridden.
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Create an XmlAttributeOverrides object.
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Using the Add method, add the XmlAttributes object to the XmlAttributeOverrides object. If the object being overridden is an XmlRootAttribute or XmlTypeAttribute, you need only to specify the type of the overridden object. But if you are overriding a field or property, you must also specify the name of the overridden member.
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When constructing the XmlSerializer, pass the XmlAttributeOverrides to the XmlSerializer constructor.
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Use the resulting XmlSerializer to serialize or deserialize the derived class objects.
The following example serializes a class named Orchestra, which contains a single field named Instruments that returns an array of Instrument objects. A second class named Brass inherits from the Instrument class. The example uses an instance of the XmlAttributeOverrides class to override the Instrument field, allowing the field to accept Brass objects.
Option Explicit Option Strict Imports System Imports System.IO Imports System.Xml.Serialization Imports Microsoft.VisualBasic Public Class Orchestra Public Instruments() As Instrument End Class Public Class Instrument Public Name As String End Class Public Class Brass Inherits Instrument Public IsValved As Boolean End Class Public Class Run Public Shared Sub Main() Dim test As New Run() test.SerializeObject("Override.xml") test.DeserializeObject("Override.xml") End Sub Public Sub SerializeObject(ByVal filename As String) ' Each overridden field, property, or type requires ' an XmlAttributes object. Dim attrs As New XmlAttributes() ' Create an XmlElementAttribute to override the ' field that returns Instrument objects. The overridden field ' returns Brass objects instead. Dim attr As New XmlElementAttribute() attr.ElementName = "Brass" attr.Type = GetType(Brass) ' Add the element to the collection of elements. attrs.XmlElements.Add(attr) ' Create the XmlAttributeOverrides object. Dim attrOverrides As New XmlAttributeOverrides() ' Add the type of the class that contains the overridden ' member and the XmlAttributes to override it with to the ' XmlAttributeOverrides object. attrOverrides.Add(GetType(Orchestra), "Instruments", attrs) ' Create the XmlSerializer using the XmlAttributeOverrides. Dim s As New XmlSerializer(GetType(Orchestra), attrOverrides) ' Writing the file requires a TextWriter. Dim writer As New StreamWriter(filename) ' Create the object that will be serialized. Dim band As New Orchestra() ' Create an object of the derived type. Dim i As New Brass() i.Name = "Trumpet" i.IsValved = True Dim myInstruments() As Instrument = {i} band.Instruments = myInstruments ' Serialize the object. s.Serialize(writer, band) writer.Close() End Sub Public Sub DeserializeObject(filename As String) Dim attrOverrides As New XmlAttributeOverrides() Dim attrs As New XmlAttributes() ' Create an XmlElementAttribute to override the Instrument. Dim attr As New XmlElementAttribute() attr.ElementName = "Brass" attr.Type = GetType(Brass) ' Add the XmlElementAttribute to the collection of objects. attrs.XmlElements.Add(attr) attrOverrides.Add(GetType(Orchestra), "Instruments", attrs) ' Create the XmlSerializer using the XmlAttributeOverrides. Dim s As New XmlSerializer(GetType(Orchestra), attrOverrides) Dim fs As New FileStream(filename, FileMode.Open) Dim band As Orchestra = CType(s.Deserialize(fs), Orchestra) Console.WriteLine("Brass:") ' The difference between deserializing the overridden ' XML document and serializing it is this: To read the derived ' object values, you must declare an object of the derived type ' (Brass), and cast the Instrument instance to it. Dim b As Brass Dim i As Instrument For Each i In band.Instruments b = CType(i, Brass) Console.WriteLine(b.Name & ControlChars.Cr & b.IsValved) Next i End Sub End Class
import System.*;
import System.IO.*;
import System.Xml.Serialization.*;
public class Orchestra
{
public Instrument instruments[];
} //Orchestra
public class Instrument
{
public String name;
} //Instrument
public class Brass extends Instrument
{
public boolean isValved;
} //Brass
public class Run
{
public static void main(String[] args)
{
Run test = new Run();
test.SerializeObject("Override.xml");
test.DeserializeObject("Override.xml");
} //main
public void SerializeObject(String fileName)
{
/* Each overridden field, property, or type requires
an XmlAttributes object.
*/
XmlAttributes attrs = new XmlAttributes();
/* Create an XmlElementAttribute to override the
field that returns Instrument objects. The overridden field
returns Brass objects instead.
*/
XmlElementAttribute attr = new XmlElementAttribute();
attr.set_ElementName("Brass");
attr.set_Type(Brass.class.ToType());
// Add the element to the collection of elements.
attrs.get_XmlElements().Add(attr);
// Create the XmlAttributeOverrides object.
XmlAttributeOverrides attrOverrides = new XmlAttributeOverrides();
/* Add the type of the class that contains the overridden
member and the XmlAttributes to override it with to the
XmlAttributeOverrides object.
*/
attrOverrides.Add(Orchestra.class.ToType(), "instruments", attrs);
// Create the XmlSerializer using the XmlAttributeOverrides.
XmlSerializer s =
new XmlSerializer(Orchestra.class.ToType(), attrOverrides);
// Writing the file requires a TextWriter.
TextWriter writer = new StreamWriter(fileName);
// Create the object that will be serialized.
Orchestra band = new Orchestra();
// Create an object of the derived type.
Brass i = new Brass();
i.name = "Trumpet";
i.isValved = true;
Instrument myInstruments[] ={ i };
band.instruments = myInstruments;
// Serialize the object.
s.Serialize(writer, band);
writer.Close();
} //SerializeObject
public void DeserializeObject(String fileName)
{
XmlAttributeOverrides attrOverrides = new XmlAttributeOverrides();
XmlAttributes attrs = new XmlAttributes();
// Create an XmlElementAttribute to override the Instrument.
XmlElementAttribute attr = new XmlElementAttribute();
attr.set_ElementName("Brass");
attr.set_Type(Brass.class.ToType());
// Add the XmlElementAttribute to the collection of objects.
attrs.get_XmlElements().Add(attr);
attrOverrides.Add(Orchestra.class.ToType(), "instruments", attrs);
// Create the XmlSerializer using the XmlAttributeOverrides.
XmlSerializer s =
new XmlSerializer(Orchestra.class.ToType(), attrOverrides);
FileStream fs = new FileStream(fileName, FileMode.Open);
Orchestra band = (Orchestra)s.Deserialize(fs);
Console.WriteLine("Brass:");
/* The difference between deserializing the overridden
XML document and serializing it is this: To read the derived
object values, you must declare an object of the derived type
(Brass), and cast the Instrument instance to it.
*/
Brass b;
for (int iCtr = 0; iCtr < band.instruments.length; iCtr++) {
Instrument i = (Instrument)band.instruments.get_Item(iCtr);
b = (Brass)i;
Console.WriteLine(b.name + "\n"
+ System.Convert.ToString(b.isValved));
}
} //DeserializeObject
} //Run
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.
Reference
XmlAttributeOverrides MembersSystem.Xml.Serialization Namespace
Deserialize
Serialize
XmlSerializer
XmlAttributes
Other Resources
Introducing XML SerializationHow to: Specify an Alternate Element Name for an XML Stream
Controlling XML Serialization Using Attributes
Examples of XML Serialization
XML Schema Definition Tool (Xsd.exe)