XmlInclude

XmlInclude is an attribute in the System.Xml.Serialization namespace used to inform the XmlSerializer about additional types that may appear when serializing or deserializing objects declared as a base type. It enables proper handling of polymorphism by listing derived types that could be encountered through a base-type reference.

The attribute is applied to a base class (or interface). You can place multiple XmlInclude attributes on the base type to register several derived types. This helps the serializer know about possible types in scenarios such as serializing properties or fields that are declared as the base type but may hold instances of derived types, for example in lists or arrays.

Example:

using System.Xml.Serialization;

[XmlInclude(typeof(Cat))]

[XmlInclude(typeof(Dog))]

public class Pet

{

public string Name { get; set; }

}

public class Cat : Pet

{

public int Lives { get; set; }

}

public class Dog : Pet

{

public string Breed { get; set; }

}

In this example, a property of type Pet or a collection of Pet can contain Cat or Dog objects, and the XmlSerializer will correctly handle their serialization and deserialization.

Notes and limitations: XmlInclude only affects the XmlSerializer and is relevant for polymorphic scenarios involving base-type references. The serializer requires the involved types to be public and, typically, to provide a public parameterless constructor. XmlInclude does not apply to other serializers and does not by itself make a non-serializable type serializable.