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XmlArrayItemAttribute Class
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XmlArrayItemAttribute Class

Specifies the derived types that the XmlSerializer can place in a serialized array.

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

'Declaration
<AttributeUsageAttribute(AttributeTargets.Property Or AttributeTargets.Field Or AttributeTargets.Parameter Or AttributeTargets.ReturnValue, AllowMultiple:=True)> _
Public Class XmlArrayItemAttribute
	Inherits Attribute
'Usage
Dim instance As XmlArrayItemAttribute

/** @attribute AttributeUsageAttribute(AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Parameter|AttributeTargets.ReturnValue, AllowMultiple=true) */ 
public class XmlArrayItemAttribute extends Attribute
AttributeUsageAttribute(AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Parameter|AttributeTargets.ReturnValue, AllowMultiple=true) 
public class XmlArrayItemAttribute extends Attribute

The XmlArrayItemAttribute belongs to a family of attributes that controls how the XmlSerializer serializes or deserializes an object. For a complete list of similar attributes, see Attributes That Control XML Serialization.

You can apply the XmlArrayItemAttribute to any public read/write member that returns an array, or provides access to one. For example, a field that returns an array of objects, a collection, an ArrayList, or any class that implements the IEnumerable interface.

The XmlArrayItemAttribute supports polymorphism--in other words, it allows the XmlSerializer to add derived objects to an array. For example, suppose a class named Mammal is derived from a base class named Animal. Further suppose that a class named MyAnimals contains a field that returns an array of Animal objects. To allow the XmlSerializer to serialize both the Animal and Mammal type, apply the XmlArrayItemAttribute to the field twice, each time specifying one of the two acceptable types.

NoteNote

You can apply multiple instances of the XmlArrayItemAttribute or XmlElementAttribute to specify types of objects that can be inserted into the array.

NoteNote

The serialization of a field or property that returns an interface or array of interfaces is not supported.

For more information about using attributes, see Extending Metadata Using Attributes.

NoteNote

You can use the word XmlArrayItem in your code instead of the longer XmlArrayItemAttribute.

The following example serializes a class named Group that contains a field named Employees that returns an array of Employee objects. The example applies the XmlArrayItemAttribute to the field, thereby instructing the XmlSerializer that it can insert objects of both the base class (Employee) type and derived class type (Manager) into the serialized array.

Option Explicit
Option Strict

Imports System
Imports System.IO
Imports System.Xml.Serialization
Imports Microsoft.VisualBasic


Public Class Group
    ' The XmlArrayItemAttribute allows the XmlSerializer to insert
    ' both the base type (Employee) and derived type (Manager)
    ' into serialized arrays. 
    
    <XmlArrayItem(GetType(Manager)), _
     XmlArrayItem(GetType(Employee))> _
    Public Employees() As Employee
    
    ' Use the XmlArrayItemAttribute to specify types allowed
    ' in an array of Object items. 
    <XmlArray(), _
     XmlArrayItem(GetType(Integer), ElementName := "MyNumber"), _
     XmlArrayItem(GetType(String), ElementName := "MyString"), _
     XmlArrayItem(GetType(Manager))> _
    Public ExtraInfo() As Object
End Class

Public Class Employee
    Public Name As String
End Class

Public Class Manager
    Inherits Employee
    Public Level As Integer
End Class


Public Class Run
    
    Public Shared Sub Main()
        Dim test As New Run()
        test.SerializeObject("TypeDoc.xml")
        test.DeserializeObject("TypeDoc.xml")
    End Sub
    
       
    Public Sub SerializeObject(ByVal filename As String)
        ' Creates a new XmlSerializer.
        Dim s As New XmlSerializer(GetType(Group))
        
        ' Writing the XML file to disk requires a TextWriter.
        Dim writer As New StreamWriter(filename)
        Dim group As New Group()
        
        Dim manager As New Manager()
        Dim emp1 As New Employee()
        Dim emp2 As New Employee()
        manager.Name = "Consuela"
        manager.Level = 3
        emp1.Name = "Seiko"
        emp2.Name = "Martina"
        Dim emps() As Employee = {manager, emp1, emp2}
        group.Employees = emps
        
        ' Creates an int and a string and assigns to ExtraInfo.
        group.ExtraInfo = New Object() {43, "Extra", manager}
        
        ' Serializes the object, and closes the StreamWriter.
        s.Serialize(writer, group)
        writer.Close()
    End Sub
    
    
    Public Sub DeserializeObject(ByVal filename As String)
        Dim fs As New FileStream(filename, FileMode.Open)
        Dim x As New XmlSerializer(GetType(Group))
        Dim g As Group = CType(x.Deserialize(fs), Group)
        Console.WriteLine("Members:")
        
        Dim e As Employee
        For Each e In  g.Employees
            Console.WriteLine(ControlChars.Tab & e.Name)
        Next e
    End Sub
End Class


import System.*;
import System.IO.*;
import System.Xml.Serialization.*;

public class Group
{
    /* The XmlArrayItemAttribute allows the XmlSerializer to insert
       both the base type (Employee) and derived type (Manager) 
       into serialized arrays. 
    */
    /** @attribute XmlArrayItem(Manager.class)
        @attribute XmlArrayItem(Employee.class)
     */
    public Employee employees[];

    /* Use the XmlArrayItemAttribute to specify types allowed
       in an array of Object items. 
    */
    /** @attribute XmlArray()
     */
    /** @attribute XmlArrayItem(int.class, ElementName = "MyNumber")
        @attribute XmlArrayItem(String.class, ElementName = "MyString")
        @attribute XmlArrayItem(Manager.class)
     */
    public Object extraInfo[];
} //Group

public class Employee
{
    public String name;
} //Employee

public class Manager extends Employee
{
    public int level;
} //Manager

public class Run
{
    public static void main(String[] args)
    {
        Run test = new Run();
        test.SerializeObject("TypeDoc.xml");
        test.DeserializeObject("TypeDoc.xml");
    } //main

    public void SerializeObject(String fileName)
    {
        // Creates a new XmlSerializer.
        XmlSerializer s = new XmlSerializer(Group.class.ToType());

        // Writing the XML file to disk requires a TextWriter.
        TextWriter writer = new StreamWriter(fileName);
        Group group = new Group();
        Manager manager = new Manager();
        Employee emp1 = new Employee();
        Employee emp2 = new Employee();

        manager.name = "Consuela";
        manager.level = 3;
        emp1.name = "Seiko";
        emp2.name = "Martina";

        Employee emps[] = new Employee[] { manager, emp1, emp2 };
        group.employees = emps;

        // Creates an int and a string and assigns to ExtraInfo.
        group.extraInfo = new Object[] { (Int32)43, "Extra", manager };

        // Serializes the object, and closes the StreamWriter.
        s.Serialize(writer, group);
        writer.Close();
    } //SerializeObject

    public void DeserializeObject(String fileName)
    {
        FileStream fs = new FileStream(fileName, FileMode.Open);
        XmlSerializer x = new XmlSerializer(Group.class.ToType());
        Group g = (Group)(x.Deserialize(fs));

        Console.WriteLine("Members:");
        for (int iCtr = 0; iCtr < g.employees.length; iCtr++) {
            Employee e = (Employee)g.employees.get_Item(iCtr);
            Console.WriteLine("\t" + e.name);
        }
    } //DeserializeObject
} //Run

System.Object
   System.Attribute
    System.Xml.Serialization.XmlArrayItemAttribute

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 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.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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