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XmlAttributeOverrides Class

Allows you to override property, field, and class attributes when you use the XmlSerializer to serialize or deserialize an object.

Namespace:  System.Xml.Serialization
Assembly:  System.Xml (in System.Xml.dll)

public class XmlAttributeOverrides

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:

  1. Create an XmlAttributes object.

  2. 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.

  3. 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.

  4. Create an XmlAttributeOverrides object.

  5. 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.

  6. When constructing the XmlSerializer, pass the XmlAttributeOverrides to the XmlSerializer constructor.

  7. 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.

using System;
using System.IO;
using System.Xml.Serialization;

public class Orchestra
{
   public Instrument[] Instruments;
}   

public class Instrument
{
   public string Name;
}

public class Brass:Instrument
{
   public bool IsValved;
}

public class Run
{
    public static void Main()
    {
       Run test = new Run();
       test.SerializeObject("Override.xml");
       test.DeserializeObject("Override.xml");
    }

    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.ElementName = "Brass";
      attr.Type = typeof(Brass);

      // Add the element to the collection of elements.
      attrs.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(typeof(Orchestra), "Instruments", attrs);

      // Create the XmlSerializer using the XmlAttributeOverrides.
      XmlSerializer s = 
      new XmlSerializer(typeof(Orchestra), 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();
   }

   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.ElementName = "Brass";
      attr.Type = typeof(Brass);

      // Add the XmlElementAttribute to the collection of objects.
      attrs.XmlElements.Add(attr);

      attrOverrides.Add(typeof(Orchestra), "Instruments", attrs);

      // Create the XmlSerializer using the XmlAttributeOverrides.
      XmlSerializer s = 
      new XmlSerializer(typeof(Orchestra), 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;
      foreach(Instrument i in band.Instruments) 
      {
         b = (Brass)i;
         Console.WriteLine(
         b.Name + "\n" + 
         b.IsValved);
      }
   }
}
#using <mscorlib.dll>
#using <System.Xml.dll>
#using <System.dll>
using namespace System;
using namespace System::IO;
using namespace System::Xml::Serialization;

public __gc class Instrument
{
public:
   String* Name;
};

public __gc class Brass:public Instrument
{
public:
   bool IsValved;
};

public __gc class Orchestra
{
public:
   Instrument* Instruments[];
};   

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->ElementName = S"Brass";
   attr->Type = __typeof(Brass);

   // Add the element to the collection of elements.
   attrs->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(__typeof(Orchestra), S"Instruments", attrs);

   // Create the XmlSerializer using the XmlAttributeOverrides.
   XmlSerializer* s = 
      new XmlSerializer(__typeof(Orchestra), 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 = S"Trumpet";
   i->IsValved = true;
   Instrument* myInstruments[] = {i};
   band->Instruments = myInstruments;

   // Serialize the object.
   s->Serialize(writer,band);
   writer->Close();
}

void DeserializeObject(String* filename)
{
   XmlAttributeOverrides* attrOverrides = 
      new XmlAttributeOverrides();
   XmlAttributes* attrs = new XmlAttributes();

   // Create an XmlElementAttribute to override the Instrument.
   XmlElementAttribute* attr = new XmlElementAttribute();
   attr->ElementName = S"Brass";
   attr->Type = __typeof(Brass);

   // Add the XmlElementAttribute to the collection of objects.
   attrs->XmlElements->Add(attr);

   attrOverrides->Add(__typeof(Orchestra), S"Instruments", attrs);

   // Create the XmlSerializer using the XmlAttributeOverrides.
   XmlSerializer* s = 
      new XmlSerializer(__typeof(Orchestra), attrOverrides);

   FileStream* fs = new FileStream(filename, FileMode::Open);
   Orchestra* band = dynamic_cast<Orchestra*> (s->Deserialize(fs));
   Console::WriteLine(S"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;
   System::Collections::IEnumerator* myEnum = band->Instruments->GetEnumerator();
   while (myEnum->MoveNext())
   {
      Instrument* i = __try_cast<Instrument*>(myEnum->Current);
      b = dynamic_cast<Brass*>(i);
      Console::WriteLine(S"{0}\n{1}", b->Name, __box(b->IsValved));
   }
}

int main()
{
   SerializeObject(S"Override.xml");
   DeserializeObject(S"Override.xml");
}

System.Object
  System.Xml.Serialization.XmlAttributeOverrides

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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