XmlArrayItemAttribute.IsNullable XmlArrayItemAttribute.IsNullable XmlArrayItemAttribute.IsNullable XmlArrayItemAttribute.IsNullable Property


Gets or sets a value that indicates whether the XmlSerializer must serialize a member as an empty XML tag with the xsi:nil attribute set to true.

 property bool IsNullable { bool get(); void set(bool value); };
public bool IsNullable { get; set; }
member this.IsNullable : bool with get, set
Public Property IsNullable As Boolean

Property Value

true if the XmlSerializer generates the xsi:nil attribute; otherwise, false, and no instance is generated. The default is true.


The following example serializes a class named Group, which contains a field named Employees that returns an array of Employee objects. A second class named Manager derives from Employee. An XmlArrayItemAttribute specifies that the XmlSerializer can insert both Employee and Manager objects into the array. The example sets the IsNullable property, thereby telling the XmlSerializer not to generate the xsi:nil attribute objects in the array set to null.

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

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

public ref class Employee
   String^ Name;

public ref class Manager: public Employee
   int Level;

public ref class Group


void SerializeObject( String^ filename )
   XmlSerializer^ s = gcnew XmlSerializer( Group::typeid );

   // To write the file, a TextWriter is required.
   TextWriter^ writer = gcnew StreamWriter( filename );

   // Creates the object to serialize.
   Group^ group = gcnew Group;

   // Creates a null Manager object.
   Manager^ mgr = nullptr;

   // Creates a null Employee object.
   Employee^ y = nullptr;
   array<Employee^>^temp = {mgr,y};
   group->Employees = temp;

   // Serializes the object and closes the TextWriter.
   s->Serialize( writer, group );

int main()
   SerializeObject( "TypeDoc.xml" );
using System;
using System.IO;
using System.Xml.Serialization;

public class Group
   [XmlArray(IsNullable = true)]
   [XmlArrayItem(typeof(Manager), IsNullable = false),
   XmlArrayItem(typeof(Employee), IsNullable = false)]
   public Employee[] Employees;

public class Employee
   public string Name;

public class Manager:Employee
   public int Level;

public class Run
   public static void Main()
      Run test = new Run();

   public void SerializeObject(string filename)
      XmlSerializer s = new XmlSerializer(typeof(Group));

      // To write the file, a TextWriter is required.
      TextWriter writer = new StreamWriter(filename);

      // Creates the object to serialize.
      Group group = new Group();

      // Creates a null Manager object.
      Manager mgr = null;
      // Creates a null Employee object.
      Employee y = null;
      group.Employees = new Employee[2] {mgr, y};

      // Serializes the object and closes the TextWriter.
      s.Serialize(writer, group);


Option Explicit
Option Strict

Imports System.IO
Imports System.Xml.Serialization

Public Class Group
    <XmlArray(IsNullable := True), _
     XmlArrayItem(GetType(Manager), IsNullable := False), _
     XmlArrayItem(GetType(Employee), IsNullable := False)> _
    Public Employees() As Employee
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()
    End Sub    
    Public Sub SerializeObject(filename As String)
        Dim s As New XmlSerializer(GetType(Group))
        ' To write the file, a TextWriter is required.
        Dim writer As New StreamWriter(filename)
        ' Creates the object to serialize.
        Dim group As New Group()
        ' Creates a null Manager object.
        Dim mgr As Manager = Nothing
        ' Creates a null Employee object.
        Dim y As Employee = Nothing
        group.Employees = New Employee() {mgr, y}
        ' Serializes the object and closes the TextWriter.
        s.Serialize(writer, group)
    End Sub
End Class


The XML schema specification for structures allows an XML document to explicitly signal that an element's content is missing. Such an element contains the attribute xsi:nil set to true. For more information, see the World Wide Web Consortium specification titled XML Schema Part 1: Structures.

If the IsNullable property is true, the xsi:nil attribute is generated for class members that have been set to null. For example, if you set a field named MyStringArray to null, the XmlSerializer generates the following XML code.

<MyStringArray xsi:nil = "true" />  

If the IsNullable property is false, no XML element is generated.


You cannot apply the IsNullable property to a member typed as a value type because a value type cannot contain null.

Applies to