BinaryFormatter: Serializing an object's base class

[Ennis Ray Lynch Jr]

I didn't know that, I just assumed a constructor would be called.

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[mav northwind]

Thanks for the suggestion, I'll take a look. Jeez, I didn't expect it to get so complicated... ;P

Regards, mav -- Black holes are the places where God divided by 0...

[Mark Salsbery]

I was trying to convince myself more than you I think :) I knew I read it somewhere once, and testing confirmed it. Its obscurely "documented" here[^]. I appreciate the discussion, thanks! Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Mark Salsbery]

I was bored, so I tried it. Works great :)

\[Serializable\]
public class Animal
{
	public string str
	{
		get;
		set;
	}
}

\[Serializable\]
public class Dog : Animal
{
	\[NonSerialized\]  `//<-- Optional!`
	public Int32 A;

	\[NonSerialized\]  `//<-- Optional!`
	public Int32 B;

	public Dog()
	{
		A = 5;
		B = 10;
	}
}

sealed class DogToAnimalDeserializationBinder : SerializationBinder
{
	public override Type BindToType(string assemblyName, string typeName)
	{
		Type typeToDeserialize = null;

		String assemVer1 = Assembly.GetExecutingAssembly().FullName;
		String typeVer1 = "Dog";

		if (assemblyName == assemVer1 && typeName == typeVer1)
		{
			typeName = "Animal";
		}

		// The following line of code returns the type.
		typeToDeserialize = Type.GetType(String.Format("{0}, {1}",
			typeName, assemblyName));

		return typeToDeserialize;
	}
}

...

Dog dog = new Dog();
dog.A = 3;
dog.B = 5;
dog.str = "Animal String";

MemoryStream MemStream = new MemoryStream();

// Serialize a Dog object
BinaryFormatter Serializer = new BinaryFormatter();
Serializer.Serialize(MemStream, dog);

MemStream.Seek(0, SeekOrigin.Begin);

// Deserialize as an Animal object
Serializer.Binder = new DogToAnimalDeserializationBinder();
Animal animal = (Animal)Serializer.Deserialize(MemStream);

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Mark Salsbery]

Wow - my code was overcomplicated. The Binder there is completely unnecessary :rolleyes:

mav.northwind wrote:

The other side of the line (where the object is supposed to be deserialized) doesn't know about Dogs, it only knows about Animals (i.e. there's only the assembly defining Animal available, not the one defining Dog, so trying to deserialize this object will throw a TypeLoadException).

I just noticed that post. The only way that's going to work is to serialize an Animal object in the first place, as you already know. The deserializing end could use a custom binder to deserialize a Dog, but that would still require that end to have the assembly implementing the Dog class. Basically I helped get you back where you started, sorry! :)

Mark Salsbery Microsoft MVP - Visual C++ :java:

[mav northwind]

Hmmm, I've played around with the SerializationBinder a bit, but didn't get a useable result either. If I always return typeof(Animal) as target type in BindToType, then the deserializing end doesn't require knowledge about Dog, but unfortunately it doesn't work because then even Animal's properties aren't deserialized if I have a Dog object in my serialization stream. :(

Regards, mav -- Black holes are the places where God divided by 0...

[mav northwind]

Thanks for the link, it was quite instructive, although I couldn't achieve useable results so far with a SerializationBinder... Nevertheless: thanks for taking your time.

Regards, mav -- Black holes are the places where God divided by 0...

[Mark Salsbery]

Right. The only way I can see to do it, if the deserialization end has no access to the Dog class (or an equivalent class), is to add a method to Dog that returns an Animal object and serialize that object. It's really unconventional anyway....it generally doesn't make sense to only serialize the base class portion of an object. But if you have a special need I suppose you need a special solution. :) Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[mav northwind]

I think I got it! After your and Giorgi's hints concerning the SerializationBinder, I looked at BinaryFormatter's other properties and found SurrogateSelector and subsequently ISerializationSurrogate. Using these two interfaces I was able to control the serialization process in a way that only Animal's properties are being serialized and during deserialization a real Animal object is being created. This should do the trick... Thanks for taking your time!

Regards, mav -- Black holes are the places where God divided by 0...

[Mark Salsbery]

Very cool! Thanks for the update! Cheers, Mark

Mark Salsbery Microsoft MVP - Visual C++ :java: