Triggering signalr hub methods, outside of the hub

Question

I need to implement some push notfications for my asp.net core 2.2 site. I found signalr, and started looking at it. I have tried implementing a small toy example, and I now have a hub class that looks as so:

As simple as can be. I now have a controller from which I need to trigger a push notification on the client computer. which could be triggered by thus controller being hit (In my real project, I need to send a push notification when a user is online, and when a new article is published on my site). So here is my controller:

public class msgController : Controller
{
public IActionResult Index()
{
return Content("serving content");
}
}

But I now need to somehow trigger my hub's sendMessage function. I'm able to call it if I just put the hub inside the controller, like this:

public class msgController : Controller
{
private IHubContext<NotificationHub> _hub;
public msgController(IHubContext<NotificationHub> hub)
{
_hub = hub;
}
public IActionResult Index()
{
_hub.Clients.All.SendAsync("ReceiveMessage", "bruger", "besked");
return Content("serving content");
}
}

But I would like to use my actual Hub class, and also, none of the docs that I can find do it like this. How could I do this?

I've seen some places giving answers that does'nt really make a lot of sense to me, like just accessing the contexthub, through a GlobalHost, that is'nt available to me. Other places claim that this just is'nt possible.

So how do I call/trigger my hub, and send a message to the client? Also, the version of my site where the hub is just written in the controller works now, and a sendmesage() function is called. But I can't really see the message being sent clientside. Where can I find it?

GlobalHost is not available in .net core, this is a .net full signalR version. What's wrong with IHubContext injection? this is exactly the way to do what you want. — Maxim Zabolotskikh, Jun 21 '21 at 08:51
hmm, it's because I want my hub to contain all the other methods assoicated with the hub. Things like onconnected and so on — BinaryGarste, Jun 21 '21 at 09:25
Well, you simply can't get the Hub without the HubContext. Go with the answer by @Kiril1512 or wrap your hub in another class (inject it with HubContext). Add to the wrapper the methods you need and than use the wrapper everywhere. — Maxim Zabolotskikh, Jun 21 '21 at 14:08

Kiril1512 · Accepted Answer · 2021-06-21T15:23:07.537

You just need to declare an interface with your hub methods like:

public interface ISignalRHub
{
    /// <summary>
    /// Broadcasts the chart data.
    /// </summary>
    /// <param name="chartData">The chart data.</param>
    Task BroadcastChartData(List<ChartModel> chartData);

    /// <summary>
    /// Broadcasts the message.
    /// </summary>
    /// <param name="message">The message.</param>
    Task BroadcastMessage(string message);

    /// <summary>
    /// Broadcasts the message.
    /// </summary>
    /// <param name="message">The chat message.</param>
    Task BroadcastMessage(ChatMessage message);
}

and define it in the hub:

public class SignalRHub : Hub<ISignalRHub>

then after injecting it in the controller:

public msgController(IHubContext<SignalRHub, ISignalRHub> hub)
{
  _hub = hub;
}

So if you want send a message to client just create a method in the hub and declare it in your interface. Because with IHubContext you can't directly call a specific hub method or client.

As said in the Microsoft documentation:

When client methods are called from outside of the Hub class, there's no caller associated with the invocation. Therefore, there's no access to the ConnectionId, Caller, and Others properties.

You can see this signalr example project, soon I will add an push notifications example: https://github.com/Kiril1512/SignalRDemo — Kiril1512, Jun 21 '21 at 14:04
really cool project! There is one thing though. I can't seem to figure out where the sending of messages actually happens? I can find the hub class, but I can't find anywhere where it seems like the message is sent — BinaryGarste, Jun 23 '21 at 15:30
On the worked example it happens with `await this.hub.Clients.All.BroadcastChartData(DataManager.GetData());` so in the client side there is a signalR listner that is listening on the method like: `private addMessageListener = () => { this.hubConnection.on('BroadcastMessage', (message: Message) => { this.message = message; this.messages.push(this.message); console.log(message); }); }` — Kiril1512, Jun 23 '21 at 15:34

Triggering signalr hub methods, outside of the hub

1 Answers1