SignalR offers a couple of ways to exclude entire sets of connections from a broadcast; here, we see how we can exclude a specific set of connected clients using their ConnectionId properties.

To demonstrate this feature, we need a slightly more complex sample. Let's consider a case where some of the messages should go unobserved by the specific clients we do not want to target. In such a case, we would need to inform everybody about who else is connected, and provide a way to pick some of those in order to exclude them from the next broadcast. To achieve this, we store a list of all the received connections in a static Hashset member inside the hub, and we send this set to every connected client when it calls a Subscribe() method. This set of connections will be used by the client to show a list of identifiers from which the user can select who to exclude when performing the broadcast of the message. To keep the UI simple, we'll let the...