WCF service method has different return value than the corresponding proxy in Client application

Question

I wrote WCF service library with the following method:

    [OperationContract]
    IEnumerable<string> GetMyMessages(char player);

I added the service library using Add Service Reference to the client application, but on the Client side the proxy method ha signature

    string[] GetMyMessages(char player);

So, when I try to return the value to a List reference I get the following error:

Cannot implicitly convert type 'string[]' to 'System.Collections.Generic.List'

Why does this happen? How can I set the return value of the proxy method to be the same as the one in the original method?

Answer 1

There's a couple of things going on here, I believe.

First, you're service method is returning an IEnumerable<T>, and I'm pretty sure that can't be serialized. How do you serialize an interface? There's no data to serialize. I would suggest converting your return type to List<string>.

Secondly, when you add a service reference the default behavior for collections is to use System.Array. You can change this by clicking on the "Advanced" button in the Add Service Reference dialog:

Then in the Service Reference Settings dialog, under Data Type you can set the Collection Type (note that there is no Systems.Collections.Generic.IEnumerable<T> option):

You could modify your operation contract as follows:

[OperationContract]
List<string> GetMyMessages(char player);

and change the default data type for collections (as above). Then modify your client to expect a List<string> result as opposed to an IEnumerable<string>.

If you really need or want an IEnumerable<T> on the client side, you could do the following in your client code:

List<string> myList = myServiceClient.GetMyMessages('a');
IEnumerable<string> myEnumerable = myList;