I have a WF service that I'm trying to setup receive activities to "Subscribe" and "Unsubscribe". I'm using This WF Durable Duplex Tutorial as a basis because my service performs callbacks to clients. Basically, think of it as a chat service.

I can make client calls to the two receive activities just fine. What happens is the callback address of the client is passed in to Subscribe() on the service. The address is stored as a variable in the WF service and everything looks like it would work as to be expected.

When a client calls Unsubscribe(), my watch I have set on the address var during debugging shows it as null. So what gives?

Here's the basic setup of my WF service layout...

Everything is enveloped in a DoWhile activity. Inside of that is a Pick activity and two Pick branches. The first branch is for subscribing activities. It has a receive-sendreply activity that assigns the string passed by the client to the WF address var. The second branch handles unsubscribing. The trigger is the Request activity and the client address is again passed in.

From there it goes into a sequence, starting with an If. It checks to see if the unsubscribeAddress equals the address already subscribed. If it does, then it sets the address to String.Empty and sends a success message back to the client.

Why would a variable that's scoped to the enveloping DoWhile activity be implicitly assigned to null? I'm trying to get this to work so I can implement multiple client subscribers from there and work on triggers that invoke callbacks to multiple clients.

CONCAT EDIT: I set a breakpoint at the DoWhile level and my var is null once Unsubscribe() is called. When Subscribe() is invoked, the watch shows a value in the var all the way through. Until I Unsubscribe() with a client. Should I be using a While Activity instead?