Question

Can I avoid adding additional fields to a class to store data which is needed only for deserialization/serialization?

Suppose I have some class:

[Serializable]
class MyClass {
      [NonSerialized]
      NonSerializableDataType myField;

      SomeOtherDataType serializableTemporaryData;

      [OnSerializing]
      OnSerializing (StreamingContext context) {
          // build serializableTemporaryData from myField
      }

      [OnDeserialized]
      void OnDeserialized (StreamingContext context) {
         // build myField from serializableTemporaryData
      }
}

Is there any way to avoid having the serializableTemporaryData field in each object of MyClass? Can I, for example, make it static (possibly by changing my On… methods)?

Constraint: I cannot change the implementation of NonSerializableDataType.

Example: Suppose myField contains a handle to a resource. Then, on serialization, I must store some information on how to acquire the resource after de-serialization, but I cannot store the handle itself. If I wrap the handle into another class, then I have just shifted the problem to the wrapper class — I would ask the very same question for the wrapper class then.

Answer 1

If you need to control the serialization process, you should implement the ISerialization interface.

[Serializable]
public class MyClass: ISerializable
{
    // As you are in control of serialization process now
    // [Serialized] and [NonSerialized] attributes are no longer required
    private NonSerializableDataType myField;

    public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        // Create and populate your SomeOtherDataType local variable here, then push it into info variable
        // Or even better, dont create SomeOtherDataType, just put additional serialization data into info variable, for example:
        info.AddValue("URL", "http://this.way.com");
    }

    protected MyClass(SerializationInfo info, StreamingContext context)
    {
        // Dont forget to define constructor for deserialization purpose

        this.myField = new NonSerializableDataType(loadFromURL: (string)info.GetValue("URL", typeof(string)));
    }
}

No additional class just for serialization data, no fields pollution. The only potential problem is to watch for any serializable data derived from this class (overwrite GetObjectData(...) if needed).

More info: MSDN ISerializable