WCF / Web Service: Databinding? Callback? Async? I'm not sure...

Question

I'm not sure what the correct method or name to do what I want to do is called, or how it's implemented. My aim is to setup a client that can be updated from the server without a call to the server.

Basically, the following scenario:

1. Client(1) calls Web Service (GetListOfProducts)
2. Server returns an array (A, B, C, D) to Client(1).
3. Client(2) calls Web Service (UpdateProductList) to remove product C.
4. Server removes product C from list and returns success to Client(2).
5. Server updates Client(1).
6. Client(1) updates its listbox and removes item C from the list.

Is Step 5 even possible? Having the server update a client when previous data requested is changed? It seems like this requires databinding, but can it be done across a web service? Oh, and is it possible to do it using HTTP Soap?

Answer 1

Yes; this is called a WCF Callback. Also see the "gotcha's" listed here; they get a bit complex when you consider reentrancy, multiple instances, and multithreading.

Answer 2

Step is very possible - what you need is some standard protocol for the server to send changes to the clients. Clients register for changes, obviously. There are various ways - from callbacks to regular polling. Nothing particularly hard aout it, though reentrance can be hard if you do not deal with multiple threads regularly.