SignalR cannot send a message to all connected clients

Question

I am trying to using SignalR to send a message to all connected clients.

I have found several examples and added what I think to be all the required bits. I did successfully get my client to connect to my Hub. I cannot get my server to connect to my Hub and send a message to all the connected clients.

When I call DatabaseChangeListener::Notify() it never hits the code in the Hub.

Can anyone suggest what else I need to do?

I am using .NET Core 2.1 preview 2 in web application with React and Redux.

I am using SignalR 1.0.0-preview2-final

I am using SignalR.Client 1.0.0-preview2-final

In Startup.cs

    public void ConfigureServices(IServiceCollection services)
    {
      // remove all other code for this question
      services.AddSignalR();
    }

    public void Configure(IApplicationBuilder app)
    {
      // remove all other code for this question
      app.UseSignalR(routes =>
      {
        routes.MapHub<SignalRHub>("/hubs/update");
      });
    }

My Hub

    [Authorize]
    public class SignalRHub : Hub
    {
        public async Task Send(string message)
        {
            await Clients.All.SendAsync("SendMessage", Context.User.Identity.Name, message);
        }   
    }

My class to notify clients

public class DatabaseChangeListener : IDatabaseChangeListener
{
    private readonly IHubContext<SignalRHub> _hubContext;

    public DatabaseChangeListener(IHubContext<SignalRHub> hubContext)
    {
            _hubContext = hubContext;

    }

    public void Notify()
    {
      _hubContext.Clients.All.SendAsync("SendMessage", "something changed, Yo");
    }
}

I supose that you did not start the connection from client. Can you show this code? — Stephu
It’s safe to remove your Send method within the SignalRHub if you only intend to send messages using IHubContext. The method in the hub is only called when you receive a message from a client, not to them. — joakimriedel

Mike Mike · Accepted Answer · 2018-07-12T23:23:20

You need to make the connection to the hub via client side and then by using your _hubContext, you should be able to send a message to the client based off of the connection made to the hub.

Connection to the hub from client side using JS.

    const connection = new signalR.HubConnectionBuilder()
        .withURL("/YourHub")
        .build();

Then after the connection is made, you can make the method to send a message to the client from the server using JS as well.

    connection.on("SendMessage", message => {
        document.getElementById("IdOfElementToDisplayMessage").innerHTML = message;
    });

Finally add:

    connection.start().catch(err => console.error(err.toString()));

Now you have established the connection to the hub via client side and can now reference the connection to the hub from the IHubContext. To send a message from the server to the client you can use _hubContext.

In your case you can call Notify() and then await _hubContext.Clients.All.SendAsync("SendMessage", "something changed, Yo"); which should send your message to the SendMessage method created in JS: connection.on("SendMessage", message => { ...

If your _hubContext variable is null during the execution then the injection of the IHubContext needs to be checked.

SignalR cannot send a message to all connected clients

1 Answers