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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.

System.Object
  System.Xml.Serialization.XmlAttributeOverrides

Namespace:  System.Xml.Serialization
Assemblies:   System.Xml (in System.Xml.dll)
  System.Xml.XmlSerializer (in System.Xml.XmlSerializer.dll)

'Declaration
Public Class XmlAttributeOverrides

The XmlAttributeOverrides type exposes the following members.

  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryXmlAttributeOverridesInitializes a new instance of the XmlAttributeOverrides class.
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  NameDescription
Public propertySupported by the XNA FrameworkSupported by Portable Class LibraryItem(Type)Gets the object associated with the specified, base-class, type.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibraryItem(Type, String)Gets the object associated with the specified (base-class) type. The member parameter specifies the base-class member that is overridden.
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  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryAdd(Type, XmlAttributes)Adds an XmlAttributes object to the collection of XmlAttributes objects. The type parameter specifies an object to be overridden by the XmlAttributes object.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryAdd(Type, String, XmlAttributes)Adds an XmlAttributes object to the collection of XmlAttributes objects. The type parameter specifies an object to be overridden. The member parameter specifies the name of a member that is overridden.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibraryFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibraryMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryToStringReturns a string that represents the current object. (Inherited from Object.)
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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.

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

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

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