Question

I am currently developing a C# Windows Form Application that I intend to let it interact with a server. The server will receive posting from a mobile application that I have developed and whenever a posting is received, my Windows Form Application should be notified and give me a notification. In order to do this, I intend to use WCF duplex service for it.

E.g. My mobile application sends an posting over to my server. Once my server reads and receives the new posting, the service should send a message over to my winform app to alert me that a posting is received. And the UI of the winform app should update accordingly to what I want to updated. (e.g. adding new panels)

This is basically how I wish for it to work
They way this would work is

1. WCF Service in running on my server
2. Windows Form connects to my server’s WCF service using Duplex Contract
3. Mobile app posts to a webpage
4. Once the webpage receives the posting, the asp.net will invoke the WCF service
5. WCF duplex service receives the posting and sends the information to the winform app
6. My winform Application aka WCF Client updates UI with this new message received

My question is, how does step 4 proceed to step 5? To be specific, how does the service sends the information over to the winform app upon receiving the posting.

To be even more specific, once the posting is received from the webpage, the service contract is invoked and the information is sent and received by the service, how does the service make use of the call back channel to send the information over to the winform app and update the UI accordingly?

Answer 1

The answer to this question depends on how your WCF service is hosted and how “big” the service will eventually be (in terms of number of simultaneous clients).

• The simplest scenario is a self-hosted WCF service (meaning hosted in a Windows Service or as a desktop application–not in IIS). In this case, you can use InstancePerSession mode and make your service use sessions. In this case, you’ll have a 1:1 correspondence between clients and instances of your service class. When a client connects, retrieve the callback reference and store it in a static list outside of the service class. When you need to send a message to one or more clients, simply iterate over (or find the desired client in) your list and call the appropriate function on the callback contract
• If you need to host your service in IIS, then the situation is trickier because you have the possibility of multiple processes hosting your service, so your list can potentially get fragmented (or blown away in the event of an app pool recycle). In this case, you’ll have to use something external to your service (MSMQ, perhaps) to notify other application pool processes that a message needs to be sent.