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 (www.w3.org) specification, "XML Schema Part 1: Structures".

If the IsNullable property is set to true, the xsi:nil attribute is generated for class members that have been set to nullNothingnullptra null reference (Nothing in Visual Basic). For example if you set a field named MyStringArray to nullNothingnullptra null reference (Nothing in Visual Basic), the XmlSerializer generates the following XML code.

 <MyStringArray xsi:nil = "true" />

If the IsNullable property is false, no XML element is generated for class members that have been set to nullNothingnullptra null reference (Nothing in Visual Basic).

Note:
You cannot apply the IsNullable property to a member typed as a value type because a value type cannot contain nullNothingnullptra null reference (Nothing in Visual Basic). Additionally, you cannot set this property to false for nullable value types. When such types are nullNothingnullptra null reference (Nothing in Visual Basic), they will be serialized by setting xsi:nil to true.

The following example shows a field with the XmlElementAttribute applied to it, and the IsNullable property set to false.

Public Class MyClass1
    <XmlElement(IsNullable := False)> Public Group As String
End Class

public class MyClass
{
   [XmlElement(IsNullable = false)]
   public string Group;
}

public ref class MyClass
{
public:

   [XmlElement(IsNullable=false)]
   String^ Group;
};

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

.NET Framework

.NET Compact Framework

XNA Framework

Reference