Johannes Hofmeister

This is so amazing that I almost crapped my pants . . . Compiler as Service is darn awesome. The named default parameters are pretty awesome too, I have been missing them since C.

The "dynamic" stuff needs to be taken with criticism - I guess many untrained developers such as students might mistake C# for a scripting language. I am afraid of the day I get a piece of code saying 1000x dynamic and a 1000 times var and not a single type name in it. . .

The link ist still broken but the example itself shouldn't be too complex.
The biggest problem is to route the the message from the Service Object to the UI Control. This has to be done by invoking a delegate on the form or the control itself, gently asking it do display someting for you. I usually do it with events exposed by the service class:

// IMessageService.cs:
[ExternalDataExchange]
public interface IMessageService
{
        void SendMessage(string message);
}

//MessageService.cs
public class MessageService : IMessageService
 {
        public event EventHandler<MessageReceivedEventArgs> MessageReceived;
        public void SendMessage(string message)
        {
            if (MessageReceived != null)           
                MessageReceived(this,
                    new MessageReceivedEventArgs(
                        WorkflowEnvironment.WorkflowInstanceId,
                        message));
        }
}

The EventArgs object for this Event is a simple class derived from ExternalDataEventArgs, that contains a string property for the message. To identify the sender the ExternalDataEventArgs Ctor always requires a Guid.

Now you can instantiate the service from the host application, then register to the MessageReceived Event. When received you can build a delegate that will be invoked on the form to change properties of the controls to display the message

// in form load:

ExternalDataExchangeService service = new ExternalDataExchangeService();
_runtime.AddService(service);
_messageService = new GuessingGameService();
service.AddService(_gameService);
_messageService.MessageReceived += new EventHandler<MessageReceivedEventArgs>(_messageService_MessageReceived);

// the delegate
        private delegate void UpdateDelegate();

        void _messageService_MessageReceived(object sender, MessageReceivedEventArgs e)
        {
            UpdateDelegate theDelegate = delegate()
            {
                lblMessage.Text = e.Message;
            };
            _instanceId = e.InstanceId;
            this.Invoke(theDelegate); // invokes the delegate on the form updating the control.
}

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As there has no example been distributed so far - link still broken - i decided to do it on my own, and i hope this helps. if your want my sample code (very similar to this) just message me.