Providing array or list of class objects via WCF

Question

Any example of WCF client server providing of List or Array of custom class objects would help me! But here is what I have got so far:

Here is my class system I want to provide

namespace NEN_Server.FS {
    [Serializable()]
    public class XFS {
        private List<NFS> files;
        public XFS() {
            files = new List<NFS>();
            }
        public List<NFS> Files {
            get { return files; }
            set { files = value; }
            }
        }
    }

where NFS is

namespace NEN_FS {
    public interface INFS : IEquatable<NFS> {
        string Path { get; set; }
        }
    [Serializable()]
    abstract public class NFS : INFS {
        abstract public string Path { get; set; }
        public NFS() {
            Path = "";
            }
        public NFS(string path) {
            Path = path;
            }
        public override bool Equals(object obj) {
            NFS other = obj as NFS;
            return (other != null) && ((IEquatable<NFS>)this).Equals(other);
            }
        bool IEquatable<NFS>.Equals(NFS other) {
            return Path.Equals(other.Path);
            }
        public override int GetHashCode() {
            return Path != null ? Path.GetHashCode() : base.GetHashCode();
            }
        }
    }

and providing method is :

namespace NEN_Server.WCF {
    public class NEN : INEN {
        private MMF mmf;
        public NEN() {
            mmf = new MMF();
            }
        public string GetRandomCustomerName() {
            return mmf.MMFS.Files[0].Path;
            }
        public NFS[] ls() {
            return mmf.MMFS.Files.ToArray();
            }

Interface is

<ServiceContract>
Public Interface INEN
    <OperationContract>
    Function GetRandomCustomerName() As String
    <OperationContract()>
    Function ls() As NFS()

and finally I do:

%svcutil% /language:cs /out:NEN_Protocol\NEN.cs http://localhost:8080/NEN_Server

it generates :

public NEN_FS.NFS[] ls()
{
    return base.Channel.ls();
}

I call it in my client application let files = nen.ls() and it fails with :

An unhandled exception of type 'System.ServiceModel.CommunicationException' occurred in mscorlib.dll

Additional information: The underlying connection was closed: The connection was closed unexpectedly.

on return base.Channel.ls(); line of code.

Note that providing string mmf.MMFS.Files[0].Path; works just fine

Why? What am I doing wrong? :)

All the code is available on GitHub : https://github.com/nCdy/NENFS

Answer 1

It seems to me, that fault reason is here: abstract public class NFS.
The first, consider using of data contracts with WCF:

[DataContract(IsReference = true)]
abstract public class NFS : INFS 
{
  [DataMember]
  abstract public string Path { get; set; }

  // the rest of code here
}

The second, specify known types for your data contract. Serializers on both side of a communication channel have to know, how to seralize/deserialize concrete NFS' descendant type:

[DataContract(IsReference = true)]
[KnownType(typeof(NFS1))]
[KnownType(typeof(NFS2))]
abstract public class NFS : INFS 
{
  [DataMember]
  abstract public string Path { get; set; }

  // the rest of code here
}

public class NFS1 : NFS {}
public class NFS2 : NFS {}