I've been working on an application which relies heavily on WCF to communicate. I have a very simple interface (contract) that the server supports to connect and disconnect: it exposes the methods Register() and Unregister(). When the client starts up and connects, it calls the Register() method, passing in some identification info. I save this information in a List<T> so that it can be used by the server to provide callbacks. When the client disconnects, it calls Unregister() which then removes the client from the collection.

That works well enough, right up until a client abruptly disconnects (ex. a connection error, network line goes down, etc.) Then suddenly I end up with a reference to a disconnected client on the server. If I attempt to use this connection to send a message back to the client an exception is thrown (which still works OK). It would be nice to know immediately as soon as a client disconnects.

If you are using TCP (full duplex) as the communication channel, you can do this pretty easily - note: this doesn't work for some of the other communication modes, like HTTP duplex. For those, you might have to rely on the various timeout settings in the .config file.

Here's what that ends up looking like (I happen to be taking advantage of LINQ here, but you can easily adjust that code if you're using an older vesion of the framework):