SignalR Web API send message to current user

Question

I have web app project and an angular 2 project. I would like use SignalR to send message from the server. Then I found this article about implementing it. But I don't know how to send message to the current user.

Code for send message C#:

public class EventHub : Hub
    {
        public async Task Subscribe(string channel)
        {
            await Groups.Add(Context.ConnectionId, channel);

            var @event = new ChannelEvent
            {
                Name = $"{Context.ConnectionId} subscribed",
                Data = new
                {
                    Context.ConnectionId,
                    ChannelName = channel
                }
            };

            await Publish(@event);
        }

        public async Task Unsubscribe(string channel)
        {
            await Groups.Remove(Context.ConnectionId, channel);

            var @event = new ChannelEvent
            {
                Name = $"{Context.ConnectionId} unsubscribed",
                Data = new
                {
                    Context.ConnectionId,
                    ChannelName = channel
                }
            };

            await Publish(@event);
        }

        public Task Publish(ChannelEvent channelEvent)
        {
            Clients.Caller.OnEvent(Constants.AdminChannel, channelEvent);

            return Task.FromResult(0);
        }

        public override Task OnConnected()
        {
            var @event = new ChannelEvent
            {
                Name = $"{Context.ConnectionId} connected",
                Data = new
                {
                    Context.ConnectionId,
                }
            };

            Publish(@event);

            return base.OnConnected();
        }

        public override Task OnDisconnected(bool stopCalled)
        {
            var @event = new ChannelEvent
            {
                Name = $"{Context.ConnectionId} disconnected",
                Data = new
                {
                    Context.ConnectionId,
                }
            };

            Publish(@event);

            return base.OnDisconnected(stopCalled);
        }
    }

public static class Constants
    {
        public const string AdminChannel = "admin";
        public const string TaskChannel = "tasks";
    }

public class ChannelEvent
    {
        public string Name { get; set; }

        public string ChannelName { get; set; }

        public DateTimeOffset Timestamp { get; set; }

        public object Data
        {
            get { return _data; }
            set
            {
                _data = value;
                Json = JsonConvert.SerializeObject(_data);
            }
        }
        private object _data;

        public string Json { get; private set; }

        public ChannelEvent()
        {
            Timestamp = DateTimeOffset.Now;
        }
    }

Then in my controller I create IhubContent

private readonly IHubContext _context = GlobalHost.ConnectionManager.GetHubContext<EventHub>();

and invoke my publish event:

private void PublishEvent(string eventName, StatusModel status)
{
    _context.Clients.Group(Constants.TaskChannel).OnEvent(Constants.TaskChannel, new ChannelEvent
    {
        ChannelName = Constants.TaskChannel,
        Name = eventName,
        Data = status
    });
}

But this message sent to all users. Help me to fix this issue and implement code to the send message to the current user.

Answer 1

The IHubContext object your are using has multiple methods, one of which is Clients, of type IHubConnectionContext.

In there you have Groups, Group, Clients & Client methods which abstract what you want to target.

In your case using:

_context.Clients.Client(connectionId).send(message);

should be working fine (you still need to propagate the connectionId though).

N.B.: send is a JS method that should be implemented on client-side.