XmlSerializer and OnSerializing/OnSerialized alternatives

Question

I have various complex objects that often have collections of other complex objects. Sometimes I only want to load the collections when they're needed so I need a way to keep track of whether a collection has been loaded (null/empty doesn't necessarily mean it hasn't been loaded). To do this, these complex objects inherit from a class that maintains a collection of loaded collections. Then we just need to add a call to a function in the setter for each collection that we want to be tracked like so:

public List<ObjectA> ObjectAList {
    get { return _objectAList; }
    set { 
        _objectAList = value; 
        PropertyLoaded("ObjectAList");
    }
}

The PropertyLoaded function updates a collection that keeps track of which collections have been loaded.

Unfortunately these objects get used in a webservice and so are (de)serialized and all setters are called and PropertyLoaded gets called when it actually hasn't been.

Ideally I'd like to be able to use OnSerializing/OnSerialized so the function knows if its being called legitimately however we use XmlSerializer so this doesn't work. As much as I'd like to change to using DataContractSerializer, for various reasons I can't do that at the moment.

Is there some other way to know if serialization is happening or not? If not or alternatively is there a better way to achieve the above without having to extra code each time a new collection needs to be tracked?

Answer 1

XmlSerializer does not support serialization callbacks. You have some options, though. For example, if you want to choose whether to serialize a property called ObjectAList, you can add a method:

public bool ShouldSerializeObjectAList () { /* logic */ }

If you need to know during deserialization too, you can use:

[XmlIgnore]
public bool ObjectAListSpecified {
    get { /* logic whether to include it in serialization */ }
    set { /* logic to apply during deserialization */ }
}

(although you might find - I can't be sure - that the set is only called for the true case)

The other option, of course, is to implement IXmlSerializable, but that should only be done as a last resort. It isn't fun.