Service Enabling Workflows

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Description

Part three in my short series on Workflow Foundation covers service enabling workflows. Service enabling a workflow doesn’t necessarily mean WCF, though WCF is certainly an option. In this screencast we look at leveraging services to enable activities that can run in various host environments.

This is a continuation from part 2, so you may want to view that screencast first if you haven’t seen it.

Part 1:   From Code Activity to Custom Activity

Part 2:  Activity Defaults and Validation

Files: Service Enabled Sample Files [Updated]

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The Discussion

  • User profile image
    jbienz
    I apologize in advance for the clipped audio.
  • User profile image
    JSmith
    Where is the screencast?
  • User profile image
    jbienz
    Hey JSmith. Don't know what happened to the video but I just re-uploaded it. Sorry for the trouble.
  • User profile image
    damster
    I  can't download the project files and I'd really like to check out the UI thread synchronization. Could you tell me how to get hold of the files? Thanks!

    Chris
  • User profile image
    indyfromiz
    Hi Jared,

    The link to the code seems to be broken!

    Cheers,
    indyfromoz
  • User profile image
    The Ron

    The link to the code for the Service Enabled Sample files does not work.  Are they posted?

    ron.garlit@gmail.com

     

  • User profile image
    Nossi
    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.
    }

    -----

    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.




  • User profile image
    jbienz
    Very sorry to everyone who was not able to get the sample files. I've upload them again and updated the link. Right now the file system still says 'Pending' but I hope that will be resolved tomorrow.

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