Using CallExternalMethodActivity / HandleExternalEventActivity in StateMachine

I am trying to make StateMachine perform some kind of database action between states.

So, I have an "initial" state that uses CallExternalMethodActivity to call the "BeginExecuteNonQuery" function in a class decorated with ExternalDataExchangeAttribute. After that, it uses SetStateActivity to enter the "finished" state.

The "End" state uses HandleExternalEventActivity to listen for the "EndExecuteNonQuery" event.

I can execute a local service in the "BeginExecuteNonQuery" function.

The problem is that "EndExecuteNonQuery" is null.

public class FailoverWorkflowController : IFailoverWorkflowController
{
    private readonly WorkflowRuntime workflowRuntime;

    private readonly FailoverWorkflowControlService failoverWorkflowControlService;
    private readonly DatabaseControlService databaseControlService;

    public FailoverWorkflowController()
    {
        workflowRuntime = new WorkflowRuntime();
        workflowRuntime.WorkflowCompleted += workflowRuntime_WorkflowCompleted;
        workflowRuntime.WorkflowTerminated += workflowRuntime_WorkflowTerminated;

        ExternalDataExchangeService dataExchangeService = new ExternalDataExchangeService();
        workflowRuntime.AddService(dataExchangeService);

        databaseControlService = new DatabaseControlService();
        workflowRuntime.AddService(databaseControlService);

        workflowRuntime.StartRuntime();
    }

    ...
}

      

        
        
        
      

    

...

public void BeginExecuteNonQuery(string command)
{
    Guid workflowInstanceID = WorkflowEnvironment.WorkflowInstanceId;

    ThreadPool.QueueUserWorkItem(delegate(object state)
                                     {
                                         try
                                         {
                                             int result = ExecuteNonQuery((string)state);
                                             EndExecuteNonQuery(null, new ExecuteNonQueryResultEventArgs(workflowInstanceID, result));
                                         }
                                         catch (Exception exception)
                                         {
                                             EndExecuteNonQuery(null, new ExecuteNonQueryResultEventArgs(workflowInstanceID, exception));
                                         }
                                     }, command);
}

      

        
        
        
      

    

What am I doing wrong with my implementation?

-stan