How can I serialize a Collection to send it using WCF?

Question

I am trying to send a object via WCF as parameter in this method:

[OperationContract]
bool SendProject(Project project);

and I got this if i try to call it from client:

There was an error while trying to serialize parameter project. The InnerException message was 'Type 'System.Collections.ObjectModel.Collection`1[[System.Collections.DictionaryEntry, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' with data contract name 'ArrayOfDictionaryEntry:http://schemas.datacontract.org/2004/07/System.Collections' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'. Please see InnerException for more details.

I search some info and I think that the error is how I serialize a class (a class from Dr. WPF) which is inside "project" class:

#region ISerializable

public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
{
    if (info == null)
    {
        throw new ArgumentNullException("info");
    }
            
    Collection<DictionaryEntry> entries = new Collection<DictionaryEntry>();
    foreach (DictionaryEntry entry in _keyedEntryCollection)
        entries.Add(entry);
    info.AddValue("entries", entries);
}

#endregion ISerializable

The problem is that I dont know where to put the tag "KnownType" or how to serialize correctly this Dictionary to send it as parameter using WCF.

Thanks!

The problem is that DictionaryEntry is non-generic and so WCF will not know the contracts for the keys and values. But why are you using a non-generic dictionary from .Net 1.1? Why not use a typed model? WCF is designed to work with typed models. Alternatively, if you can't use a typed model, can you share a minimal reproducible example that reproduces the problem? At the moment you just share a code fragment that don't compile standalone. — dbc
I change the DictionaryEntry for KeyValuePair<TKey, TValue> but the error just persist but this time with KeyValuePair as parameter. The Dictionary is used multiple times and it has not a type defined, it is <string, ClassA> or <string, classB>. It would be difficult send a minimal reproducible example because the code has complexity, but i think you can reproduce it dowlnoading the code from Dr.WPF link and using it in WCF in a custom class. I will try to simplify the code if this solution doesnt work. Thanks for your help! — Ugaitz
Since you're just serializing a Collection<DictionaryEntry> (or Collection<KeyValuePair<string, something you haven't shown us>>)maybe you can reproduce this with a simple Dictionary<TKey, TValue> stored inside a root object? — dbc

Ugaitz Ugaitz · Accepted Answer · 2020-08-25T06:40:55

I have the solution, which is not so clean but is a solution. As dbc said, updating DictionaryEntry to KeyValuePair<TKey,TValue> is a recommended step, but what fixed my problem was set [KnownType(typeof(Collection<KeyValuePair<TypeX, TypeY>>))] in the class where the serialization is.

How can I serialize a Collection to send it using WCF?

1 Answers