Attaching to WF4 runtime events from an IIS/WAS service

How do we attach our WorkflowServiceHostFactory to workflow level runtime events in WF4? Particularly for workflows hosted in IIS/WAS? If you're in the same boat as me, you've probably been spending more than a few minutes trying to figure out how to do this. I think in WF3 it was pretty straightforward, but in WF4 we have to approach this from a different angle.

Let's cut to the chase, here is what needs to be done to track the events we want:

Subclass from TrackingParticipant and override its Track method. Within this Track method we'll look only for TrackingRecords of type WorkflowInstanceRecord, since we only want to capture workflow level events.

NOTE: you can also attach to activity and custom level events but that's out of the scope of this blog post. I recommend this article for a more in depth description of Tracking: http://www.codeproject.com/KB/WF/WF4Extensions.aspx

If you want your application to "react" to particular workflow events, we only need to inspect the WorkflowInstanceRecord.State property. The following sample code is a generic template you can use with all the possible states I've encountered so far:

using System.Activities.Tracking;

public class WorkflowStateTrackingParticipant :TrackingParticipant

{

     protected override void Track(TrackingRecord record, TimeSpan timeout)

     {

          WorkflowInstanceRecord workflowInstanceRecord = record as WorkflowInstanceRecord;

          if(workflowInstanceRecord != null)

          {

               switch(workflowInstanceRecord.State)

               {

                    case "Started": break;
                    case "Aborted": break;
                    case "Canceled": break;
                    case "Completed": break;
                    case "Deleted": break;
                    case "Idle": break;
                    case "Persisted": break;
                    case "Resumed": break;
                    case "Successful": break;
                    case "Suspended": break;
                    case "Terminated": break;
                    case "UnhandledException": break;
                    case "Unloaded": break;
                    case "Unsuspended": break;

                    default: break;

               }

          }

     }

}

To use this class, we need to add it to the WorkflowExtensions collection of our WorkflowServiceHostFactory; we do this by subclassing from it and overriding the CreateWorkflowServiceHost methods:

     public class CustomWorkflowServiceHostFactory : WorkflowServiceHostFactory

     {

          protected override WorkflowServiceHost CreateWorkflowServiceHost(System.Activities.Activity activity, Uri[] baseAddresses)

          {

               WorkflowServiceHost host = base.CreateWorkflowServiceHost(activity, baseAddresses);

               host.WorkflowExtensions.Add(new WorkflowStateTrackingParticipant());

               return host;

          }

          protected override WorkflowServiceHost CreateWorkflowServiceHost(WorkflowService service, Uri[] baseAddresses)

          {

               WorkflowServiceHost host = base.CreateWorkflowServiceHost(service, baseAddresses);

               host.WorkflowExtensions.Add(new WorkflowStateTrackingParticipant());

               return host;

          }

     }

Finally, we need to indicate this CustomWorkflowServiceHostFactory, instead of the default one, in your Web.config or .svc files (depending on your particular implementation). In my case, I create my .svc definition files from the .xamlx workflows, dynamically, through Web.config via the serviceHostingEnvironment section:

<serviceHostingEnvironment multipleSiteBindingsEnabled="true">

     <serviceActivations>

          <add relativeAddress="MyWorkflowService.svc"

               service="Workflow.xamlx"

               factory="CustomWorkflowServiceHostFactory" />

     </serviceActivations>

</serviceHostingEnvironment>

Verify you can hit your .svc from a browser and you're done.

That's it, hopefully this post can help people save more than a few minutes of research.