SignalR - Checking if a user is still connected

Question

I have a hub with method that is called client-side. This method launches a timer with a delegate that runs every 10 seconds. Since it wouldn't make sense to keep running this delegate if no one is connected to the hub, I want to check if any users are still connected from inside the delegate before I reschedule it. Is there any way to do this?

Answer 1

Probably the most used solution is to keep a static variable containing users currently connected and overriding OnConnect and OnDisconnect or implementing IDisconnect depending on the version that you use.

You would implement something like this:

public class MyHub : Hub
{
    private static List<string> users = new List<string>();
    public override Task OnConnected()
    {
        users.Add(Context.ConnectionId);
        return base.OnConnected();
    }

    //SignalR Verions 1 Signature
    public override Task OnDisconnected()
    {
        users.Remove(Context.ConnectionId);
        return base.OnDisconnected();
    }

    //SignalR Version 2 Signature
    public override Task OnDisconnected(bool stopCalled)
    {
        users.Remove(Context.ConnectionId);
        return base.OnDisconnected(stopCalled);
    }

    // In your delegate check the count of users in your list.
}

Answer 2

If you save your connectionId in your database, you can check this:

var heartBeat = GlobalHost.DependencyResolver.Resolve<ITransportHeartbeat>();

var connectionAlive = heartBeat.GetConnections().FirstOrDefault(c=>c.ConnectionId == connection.ConnectionId);

if (connectionAlive.IsAlive)
{
//Do whatever...
}

Answer 3

From http://forums.asp.net/t/1829432.aspx/1?How+do+I+get+list+of+connected+clients+on+signalr+

IHubContext context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
context.Clients.notify("Hello world");

So you should be able to get context.Clients.Count.

That post also references the wiki which has lots of good info. You could try using the OnConnected/OnDisconnected examples to track the users, and when you get to zero users stop your call.

Answer 4

I have done this way:

public class PrincipalCommunicator
    {
        public readonly static Lazy<PrincipalCommunicator> _instance = new Lazy<PrincipalCommunicator>(
                () => new PrincipalCommunicator(GlobalHost.ConnectionManager.GetHubContext<PrincipalHub>())
            );

        public List<string> ConnectedUsers { get; set; }

        private IHubContext _context;

        private PrincipalCommunicator(IHubContext context)
        {
            ConnectedUsers = new List<string>();
            _context = context;
        }

        public static PrincipalCommunicatorInstance
        {
            get
            {
                return _instance.Value;
            }
        }

        public bool IsUserConnected(string user)
        {
            return UsuariosConectados.Contains(user);
        }
    }

    public class PrincipalHub : Hub
    {
        public override Task OnConnected()
        {
            PrincipalComunicador.Instance.UsuariosConectados.Add(Context.User.Identity.Name);

            return base.OnConnected();
        }

        public override Task OnDisconnected(bool stopCalled)
        {
            PrincipalComunicador.Instance.UsuariosConectados.Remove(Context.User.Identity.Name);
            return base.OnDisconnected(stopCalled);
        }
    }
}

This way, all logic to send something to client stays in one place, like the example and you can know if a user is connected anywhere in the code.