XML serialisation won't write out lazy-evaluated property

Question

Following on from a previous question, I am having trouble combining the Lazy<T> generic that was suggested with my XML Serialization.

Here is the functionality I am using for Lazy<T>:

public struct Lazy<T> where T : class, new()
{
    private T _Value;

    public bool HasValue
    {
        get
        {
            return (_Value != null);
        }
    }

    public T Value
    {
        get
        {
            if (!HasValue)
                _Value = new T();

            return _Value;
        }
    }
}

Now the MSDN Docs say that it's fine to have an [XmlElement("ElementName")] on a property and it does indeed seem to be able to deserialize just fine. The problem comes when I am serializing an object. I am running the following piece of code:

class SomeClass
{
    [XmlElement("ExternalElementName")]
    public ComplexElementType InternalElementName
    { 
        get { return _InternalElementName.Value; } 
    }

    protected Lazy<ComplexElementType> _InternalElementName;
}

Elsewhere:

SomeClass someClass = new SomeClass();
someClass.InternalElementName.ComplexElementTypeChild = "some string";

// serialize...

The strange thing is, this works fine in the debugger but no element is output in the XML. Non Lazy<T> elements work fine. Any ideas?

Answer 1

Not sure what the problem is (I have always found the XML serializer behaviour to be shifty), but why not use the Nullable<T> class? Don't re-invent the wheel :)

Answer 2

The problem is that the property has no setter. Even if it would be possible to get the value to serialise it, it can't be deserialised as there is no way to put the value back in the new object.

Answer 3

By design, XML Serialization will only serialize public read/write properties, and public fields.