WCF Service

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Hello,

I am working on a service for silverlight. The operation contract is defined like this :

MIDL

[ServiceContract]
    public interface IFeedbackAppProxy
    {
        [OperationContract]
        void InsertQuestions(IEnumerable<Question> questions, Action<int> callback);
        [OperationContract]
        void InsertQuestion(Question questions, Action<int> callback);
        [OperationContract]
        void InsertAnswer(MultipleChoiceAnswer answer, Action<int> callback);
        [OperationContract]
        void InsertAnswers(IEnumerable<MultipleChoiceAnswer> answer, Action<int> callback);
        [OperationContract]
        void InsertTag(Tag tag, Action<int> callback);
        [OperationContract]
        void InsertTagXQuestion(Tag tag, int questionID, Action<int> callback);
        [OperationContract]
        void InsertTags(IEnumerable<Tag> tag, Action<int> callback);
        [OperationContract]
        void InsertTagsXQuestion(IEnumerable<Tag> tag, int questionID, Action<int> callback);
    }

I also have a test project with reference to the service and the folowing dummy test method :

C#

[TestMethod]
       public void TestMethod1()
       {
           FeedbackAppProxyClient myFeedbackApp = new FeedbackAppProxyClient();
           myFeedbackApp.Open();
           myFeedbackApp.InsertQuestion(new Question(), i => { });
       }

When I debug the test method, I get :

There was an error while trying to serialize parameter http://tempuri.org/:callback. The InnerException message was 'Type 'System.DelegateSerializationHolder+DelegateEntry' with data contract name 'DelegateSerializationHolder.DelegateEntry:http://schemas.datacontract.org/2004/07/System' 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.

What should I do ?

Thank you,
Bogdan

Posted 1-Dec-10 22:50pm

Beda Bogdan

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Steve Maier · Accepted Answer · 2010-12-02T05:23:00

What you might want to do is to use the callback system that is available in WCF Services. Since your callbacks can be on a different machine and not just locally, I think you would have a problem just putting the action in that way you had. You could setup something like this...

C#

[ServiceContract(Name = "FeedbackService",
    Namespace = "http://mycompany.com/FeedbackServices",
    CallbackContract = typeof(IFeedbackAppProxyCallback),
    SessionMode = SessionMode.Required)]
public interface IFeedbackAppProxy
{
    [OperationContract]
    void Subscribe();

    [OperationContract]
    void Unsubscribe();
}

C#

public interface IFeedbackAppProxyCallback
{
    [OperationContract(IsOneWay = true)]
    void QuestionAnswered(Question q, Answer a);
}

Then in the implementation of the service for the subscribing you can add this...

C#

IFeedbackAppProxyCallback callback;

public void Subscribe()
{
    callback = OperationContext.Current.GetCallbackChannel<IFeedbackAppProxyCallback>();
}

public void Unsubscribe()
{
    callback = null;
}

Then when you need to callback from the service you can just call...

C#

callback.QuestionAnswered(questionThatWasAnswered, answerGiven);