XML Serialization for interfaces in .NET

In your quest to find out how you can support XML serialization for types that contain interfaces, you may often find yourself coming to the same answer: you cannot serialize interfaces. That is true, but you can work around it, and I will present two methods.

Write you own Xml serialization code

Refer to : http://social.msdn.microsoft.com/Forums/en-US/bac96f79-82cd-4fef-a748-2a85370a8510/xmlserialization-with-interfaces?forum=asmxandxml

This post provides a nice answer to your woes. But you should watch out for a gotcha: 

strType = m_Child.GetType().FullName;

Instead you may want to use this in case your dependant interface implementations could come from an external assembly:

string strType = m_Child.GetType().AssemblyQualifiedName 
	?? m_Child.GetType().FullName;

Use generics with constraints

You can get away with not having to write your own serialization code by using generics. This isn’t a silver bullet as it will effect your class design, and may not make sense. Take this example:

public class MyClass 
{
	public IMyInterface MyProperty { get; set; }
}

You could rewrite this to become:

public class MyClass <T> where T : IMyInterface
{
	public T MyProperty { get; set; }
}

Of course this has several implications. For example, instantiating these types become more complicated and could lead to tricker wiring/construction problems.  Another point to make is the class itself doesn’t guarantee it is XML serializable: if the class is declared with type (T) of an interface (or a non-serializable class) then it won’t be XML serializable. But this should nothing to be surprized about, the .Net frameworks  XML serializable generic types also behave like this (e.g. List<T>).

Here is another example:

public class MyCollection
{
	public IList<IMyInterface> MyProperty { get; set; }
}

Generic XML serializable version (provided T is XML serializable):

public class MyCollection <T> where T : IMyInterface
{
	public IList<T> MyProperty { get; set; }
}