Do I need to expose a constructor in a WCF DataContract for it to work during object instantiation on the client?

Question

I have a class in a WCF service, lets call it A. A is a data contract, which contains as one of its DataMembers a collection of another custom object B. To avoid Null Reference problems on the client side, I instantiate the BList in the constructor like so:

[DataContract]
public class A
{
    [DataMember]
    public String name { get; set; }
    [DataMember]
    public List<B> BList {get; set; }

    public A()
    {
        BList = new List<B>();  
    }
}

My problem is that on the client, this instantiation does not happen and BList appears as null after an object of A is created on the client. I'm guessing that the constructor does not appear on the client. So, do I need to make the constructor an explicit operation contract? If so that would make internal things visible to the client that they shouldn't see, right? How do I make sure that this instantiation happens on the client?

Thanks, and sorry if this seems like a dumb question.

Answer 1

You need to use [OnDeserializing] or [OnDeserialized] attributes to do initialization of DataContract types. See http://msdn.microsoft.com/en-us/library/ms733734.aspx

Answer 2

I am not sure if there is a way to do this but by getting the new instance from the service the list should be initialized, I suggest the following

• Write a web method that returns a new instance of your class and you might use it as the following and I am sure your list is initialized

To create the instance:

A a = new ServiceClient.CreateAInstance();

In the service write the method,

[OperationContract]
public A CreateAInstance()
{
     return new A();
}