XmlAttributeOverrides Clase

Definición

public ref class XmlAttributeOverrides

public class XmlAttributeOverrides

type XmlAttributeOverrides = class

Public Class XmlAttributeOverrides

Herencia

Object

XmlAttributeOverrides

Ejemplos

En el ejemplo siguiente se serializa una clase denominada Orchestra, que contiene un único campo denominado Instruments que devuelve una matriz de Instrument objetos . Una segunda clase denominada Brass hereda de la Instrument clase . En el ejemplo se usa una instancia de la XmlAttributeOverrides clase para invalidar el Instrument campo, lo que permite que el campo acepte Brass objetos.

#using <System.Xml.dll>
#using <System.dll>

using namespace System;
using namespace System::IO;
using namespace System::Xml::Serialization;

public ref class Instrument
{
public:
   String^ Name;
};

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

public ref class Orchestra
{
public:
   array<Instrument^>^Instruments;
};

void SerializeObject( String^ filename )
{
   /* Each overridden field, property, or type requires 
      an XmlAttributes object. */
   XmlAttributes^ attrs = gcnew XmlAttributes;

   /* Create an XmlElementAttribute to override the 
      field that returns Instrument objects. The overridden field
      returns Brass objects instead. */
   XmlElementAttribute^ attr = gcnew XmlElementAttribute;
   attr->ElementName = "Brass";
   attr->Type = Brass::typeid;

   // Add the element to the collection of elements.
   attrs->XmlElements->Add( attr );

   // Create the XmlAttributeOverrides object.
   XmlAttributeOverrides^ attrOverrides = gcnew 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::typeid, "Instruments", attrs );

   // Create the XmlSerializer using the XmlAttributeOverrides.
   XmlSerializer^ s = gcnew XmlSerializer( Orchestra::typeid,attrOverrides );

   // Writing the file requires a TextWriter.
   TextWriter^ writer = gcnew StreamWriter( filename );

   // Create the object that will be serialized.
   Orchestra^ band = gcnew Orchestra;

   // Create an object of the derived type.
   Brass^ i = gcnew Brass;
   i->Name = "Trumpet";
   i->IsValved = true;
   array<Instrument^>^myInstruments = {i};
   band->Instruments = myInstruments;

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

void DeserializeObject( String^ filename )
{
   XmlAttributeOverrides^ attrOverrides = gcnew XmlAttributeOverrides;
   XmlAttributes^ attrs = gcnew XmlAttributes;

   // Create an XmlElementAttribute to override the Instrument.
   XmlElementAttribute^ attr = gcnew XmlElementAttribute;
   attr->ElementName = "Brass";
   attr->Type = Brass::typeid;

   // Add the XmlElementAttribute to the collection of objects.
   attrs->XmlElements->Add( attr );
   attrOverrides->Add( Orchestra::typeid, "Instruments", attrs );

   // Create the XmlSerializer using the XmlAttributeOverrides.
   XmlSerializer^ s = gcnew XmlSerializer( Orchestra::typeid,attrOverrides );
   FileStream^ fs = gcnew FileStream( filename,FileMode::Open );
   Orchestra^ band = dynamic_cast<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;
   System::Collections::IEnumerator^ myEnum = band->Instruments->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Instrument^ i = safe_cast<Instrument^>(myEnum->Current);
      b = dynamic_cast<Brass^>(i);
      Console::WriteLine( "{0}\n{1}", b->Name, b->IsValved );
   }
}

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

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);
      }
   }
}

Option Explicit
Option Strict

Imports System.IO
Imports System.Xml.Serialization

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

Comentarios

XmlAttributeOverrides permite XmlSerializer invalidar la forma predeterminada de serializar un conjunto de objetos. La invalidación de la serialización de esta manera tiene dos usos: en primer lugar, puede controlar y aumentar la serialización de objetos que se encuentran en un archivo DLL, incluso si no tiene acceso al origen; en segundo lugar, puede crear un conjunto de clases serializables, pero serializar los objetos de varias maneras. Por ejemplo, en lugar de serializar miembros de una instancia de clase como elementos XML, puede serializarlos como atributos XML, lo que resulta en un documento más eficaz para el transporte.

Después de crear un XmlAttributeOverrides objeto, se pasa como argumento al XmlSerializer constructor. El resultado XmlSerializer usa los datos contenidos por para XmlAttributeOverrides invalidar los atributos que controlan cómo se serializan los objetos. Para ello, XmlAttributeOverrides contiene una colección de los tipos de objeto que se invalidan, así como un XmlAttributes objeto asociado a cada tipo de objeto invalidado. El XmlAttributes propio objeto contiene un conjunto adecuado de objetos de atributo que controlan cómo se serializa cada campo, propiedad o clase.

El proceso para crear y usar un XmlAttributeOverrides objeto es el siguiente:

1. Cree un objeto XmlAttributes.

2. Cree un objeto de atributo que sea adecuado para el objeto que se va a invalidar. Por ejemplo, para invalidar un campo o una propiedad, cree un XmlElementAttribute, mediante el nuevo tipo derivado. Opcionalmente, puede asignar un nuevo ElementNameo Namespace que invalide el nombre de atributo o el espacio de nombres de la clase base.

3. Agregue el objeto de atributo a la propiedad o colección adecuadas XmlAttributes . Por ejemplo, agregaría a XmlElementAttribute la XmlElements colección del XmlAttributes objeto , especificando el nombre de miembro que se va a invalidar.

4. Cree un objeto XmlAttributeOverrides.

5. Con el Add método , agregue el XmlAttributes objeto al XmlAttributeOverrides objeto . Si el objeto que se invalida es o XmlRootAttribute XmlTypeAttribute, solo debe especificar el tipo del objeto invalidado. Pero si reemplaza un campo o propiedad, también debe especificar el nombre del miembro invalidado.

6. Al construir , XmlSerializerpase al XmlAttributeOverrides XmlSerializer constructor .

7. Utilice el resultado XmlSerializer para serializar o deserializar los objetos de clase derivadas.

Constructores

Propiedades

Métodos

Se aplica a

Consulte también

• Deserialize(Stream)
• Serialize(TextWriter, Object)
• XmlSerializer
• XmlAttributes
• Introducir la serialización XML
• Procedimiento para especificar un nombre de elemento alternativo para una secuencia XML
• Controlar la serialización XML mediante atributos
• Ejemplos de serialización XML
• XML Schema Definition Tool (Xsd.exe)