Export (0) Print
Expand All
0 out of 2 rated this helpful - Rate this topic

XmlAttributeOverrides Class

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

For a list of all members of this type, see XmlAttributeOverrides Members.

System.Object
   System.Xml.Serialization.XmlAttributeOverrides

[Visual Basic]
Public Class XmlAttributeOverrides
[C#]
public class XmlAttributeOverrides
[C++]
public __gc class XmlAttributeOverrides
[JScript]
public class XmlAttributeOverrides

Thread Safety

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

Remarks

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 don't 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 goal, the XmlAttributeOverrides contains a collection of the object types that will be 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 will override 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 specify the type of the overridden object. But if you are overridding 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.

Example

[Visual Basic, C#, C++] 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.

[Visual Basic] 
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


[C#] 
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);
      }
   }
}


[C++] 
#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");
}

[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

Namespace: System.Xml.Serialization

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

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

See Also

XmlAttributeOverrides Members | System.Xml.Serialization Namespace | Deserialize | Serialize | XmlSerializer | Introducing XML Serialization | Overriding XML Serialization | XmlAttributes | Controlling XML Serialization Using Attributes

Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft. All rights reserved.