Question

I’m not sure exactly how to phrase this, but here goes:

I have a custom class called EmailAttachment which has 3 properties/attributes defined. An object of this class is passed to a method (in another class, of course) called UploadAttachment

void UploadAttachment(EmailAttachment attachment);

However, when I implement this using, for example,

client.UploadAttachment(emailAttachmentInstance)

Visual Studio tells me that UploadAttachment does not accept 1 argument instead it accepts 3 (ie the variables from the class definition).
This has me quite confused so any help is appreciated

---

To clarify a bit…

client is actually an instance of a WCF service. The service interface includes

[OperationContract]
void UploadAttachment(EmailAttachment attachment); //which is public.    

Following is the class in question…

[MessageContract]
public class EmailAttachment
{
    [MessageHeader(MustUnderstand = true)]
    public int EmailID;

    [MessageHeader(MustUnderstand = true)]
    public string FileName;

    [MessageBodyMember(Order = 1)]
    public Stream AttachmentFile;
}

Answer 1

So here’s my answer (partially conjecture/hypothesis of a friend)…
I guess it has to do with the nature of the WCF service. In order to prevent complications client-side (i.e. being dependent on class(es) defined by the service), the client can pass the attributes/properties (the 3 mentioned previously) of the [service] class as the arguments of the method (in this case UploadAttachment()). Therefore, it only needs to know the data types of those attributes/properties, and does not have to instantiate an object of its class. The same can be done for custom return types.
For example, if SomeClass is defined as such…

[MessageContract]
public class SomeClass
{
    [MessageBodyMember]
    public bool value;

    public SomeClass(bool value)
    {
        this.value = value;
    }
}

…and the service has a method that returns a value of SomeClass like so…

SomeClass SomeMethod();

…the client can call SomeMethod() like so…

bool someReturnValue = client.SomeMethod();

instead of having to instantiate SomeClass.

Hopefully that makes sense.