Hello,

I am trying to put an service together with a need to instantiate a new service operation, similar to the example shown on page 95.

The operation that I am creating is based on an Query operation, and per the example, I am trying to return a class which is part of the state.

However, when I attempt to return a type which is part of my service _state, I get compilation errors.

For example, the code from pg 95 shows:

public class QueryInfrared : Query<SensorsRequest, Portset<Sensors, Fault>>
{
}

What is the scope of the Sensors class? Is it defined in the _state ? If so, how can the above PortSet have knowledge about it if is defined in another class?

I've looked through the Hemmisson code and I can't seem to find the answer...

Thanks,
Scott

Oops! That one slipped past the Technical Editor!

The code on page 95 is from an early version of the Hemisson code before I decided to change it over to use the Generic Brick in Chapter 17. (It was originally a separate example in Chapter 16).

Anyway, to answer your question, the Sensors class should be in the HemissonTypes.cs file (don't bother looking in the Hemisson code -- it's not there). It must be declared as a public class, and the trick is that it must have the [DataContract] attribute, which you can see on the SensorsRequest class on page 95.

In fact, both the request and the response classes must have the [DataContract] attribute. When DssProxy creates the Proxy DLL, it recognizes this attribute and transfers the class definitions across to the proxy code so that other services can find these data types.
When you set up a reference to the Proxy DLL from your own service, your code finds out about these request/response types.

There is nothing to stop you using a public class with the [DataContract] attribute inside the state. In the original Hemisson code there was a public member in the state with the Sensors data type.

While we are on the subject, if you want the members of a class to be visible you not only have to declare them as public, you also have to mark them with [DataMember]. Have a look at GenericBrickState.cs in Chapter 17.

Trevor