Question

I’m trying to implement a custom formatter using the .NET IFormatter interface.

After a couple of hours of search, I just found a very basic sample which unfortunately doesn’t include recursion. I also tried with Reflector to look at BinaryFormatter and SoapFormatter, but they are rather complex.

My question is:
Should I implement recursion myself, or there’s something I’ve missed in FormatterServices?

Following my code:

public void Serialize(Stream serializationStream, object graph)
{
    // Get fields that are to be serialized.
    MemberInfo[] members = FormatterServices.GetSerializableMembers(graph.GetType(), Context);

    // Get fields data.
    object[] data = FormatterServices.GetObjectData(graph, members);

    // Write class name and all fields & values to file
    StreamWriter sw = new StreamWriter(serializationStream);

    string accumulator = string.Empty;
    for (int i = 0; i < data.Length; ++i)
    {
        // Skip this field if it is marked NonSerialized.
        if (Attribute.IsDefined(members[i], typeof(NonSerializedAttribute)))
            continue;

        FieldInfo field = (FieldInfo)members[i];
        if (field.FieldType.IsPrimitive)
        {
        }
        else //TODO: What should I do here?
    }
    sw.Close();
}

Answer 1

If by recursion you mean traversing through the object tree then yes, it up to you when you implement your own IFormatter.

Simply check if the value of the property is not null and if it is implementing IFormatter interface. If it is then just call it and use the value it returns.
If not then it is up to you again: you may throw an exception saying that IFormatter must be implemented, or just fall-back to some sort of default formatter (XML or Binary one).

The recursion per se is tricky. When, let’s say, the object references itself, you need to be smart enough to handle this situation and not to end up with the infinite loop:

public class A {
    public object SomeProperty { get; set; }
}
var a = new A();
a.SomeProperty = a;

There are a number of tricky aspects in implementing formatters, like what if two properties are actually reference the same object? Will you serialize/format it twice or just once and keep the information about these references somehow?
You don’t probably need this if you want just one-way serialization, but if you want to be able to restore the object it might be important…