KnownTypeAttribute Defined on Service Client But Still Has No Knowledge of Type

Question

I'm trying to get a reference type from a WCF service with Xamarin.Forms but I get an exception when I get the data back from the server.

System.Runtime.Serialization.SerializationException: Error in line 1 position 326. Element 'http://tempuri.orgtGetRecordResult' contains data of the 'http://schemas.datacontract.org/2004/07/Adapt.Model.Security:User' data contract. The deserializer has no knowledge of any type that maps to this contract.

My Code

[KnownType(typeof(User))]
public partial class DataAccessServiceClient : ClientBase<IDataAccessService>, IDataAccessService, IServiceClient
{
    public DataAccessServiceClient(Binding binding, EndpointAddress endpointAddress) : base(binding, endpointAddress)
    {

    }

    public virtual async Task OpenAsync()
    {
        await Task.Factory.FromAsync(((System.ServiceModel.ICommunicationObject)(this)).BeginOpen(null, null), new System.Action<System.IAsyncResult>(((System.ServiceModel.ICommunicationObject)(this)).EndOpen));
    }

    public virtual Task CloseAsync()
    {
        return Task.Factory.FromAsync(((System.ServiceModel.ICommunicationObject)(this)).BeginClose(null, null), new System.Action<System.IAsyncResult>(((System.ServiceModel.ICommunicationObject)(this)).EndClose));
    }

    public string Authenticate(string username, string password)
    {
        return Channel.Authenticate(username, password);
    }

    public IRecord GetRecord(string ObjectTypeName, object primaryKeyValue, ConnectionInfo connectionInfo)
    {
        return Channel.GetRecord(ObjectTypeName, primaryKeyValue, connectionInfo);
    }
}

[ServiceContract()]
public interface IDataAccessService
{
    [OperationContract()]
    string Authenticate(string username, string password);

    [OperationContract()]
    IRecord GetRecord(string ObjectTypeName, object primaryKeyValue, ConnectionInfo connectionInfo);

}

public static async Task<IDataAccessService> GetDataAccessServiceProxy()
{
    var binding = GetBinding();
    var proxy = new DataAccessServiceClient(binding, new EndpointAddress($"http://10.0.2.152/helpdeskservices/DataAccessService.svc"));
    await proxy.OpenAsync();
    return proxy;
}

private async Task DisplayTask()
{
    try
    {
        var proxy = await App.GetDataAccessServiceProxy();
        var record = proxy.GetRecord(typeof(User).FullName, 1, new Adapt.Model.Data.ConnectionInfo { AuthToken = _AuthToken });
        await DisplayAlert("info", "user details = " + (record as User)?.UserName, "test complete");
    }
    catch (Exception ex)
    {
        await DisplayAlert("error", ex.ToString() + "\n\n\n" + ex.InnerException?.ToString() ?? "No inner exception", "retry");
        await DisplayTask();
    }
}

Calling Authenticate works fine, I'm assuming because it's a value type but getting the User object has this issue.

Answer 1

You cannot use object as type of one of the arguments in GetRecord (look also at this SO question). So you have to change your GetRecord contract. One option is to define a base class for all the types you have to use and use that class in GetRecord. Then you put the KnownType declaration on that base class for all the derived classes. Look at this for an example using Person (base class) and Student/Teacher (derived class). You have the same problem with the return value IRecord. At some point you have to tell WCF how to serialize/deserialize the object represented by IRecord. See this SO question how to add KnownType's dynamically.