In ASP.NET Core SignalR, how do I send a message from the server to a client?

Question

I've successfully setup a SignalR server and client using the newly released ASP.NET Core 2.1. I built a chat room by making my ChatHub extend Hub: whenever a message comes in from a client, the server blasts it back out via Clients.Others.

What I do not yet understand is how to send a message to clients not as a response to an incoming message. If the server is doing work and produces a result, how do I gain access to the Hub in order to message particular clients? (Or do I even need access to the Hub? Is there another way to send messages?)

Searching this issue is difficult as most results come from old versions of ASP.NET and SignalR.

Answer 1

You can inject the IHubContext<T> class into a service and call the clients using that.

public class NotifyService
{
    private readonly IHubContext<ChatHub> _hub;

    public NotifyService(IHubContext<ChatHub> hub)
    {
        _hub = hub;
    }

    public Task SendNotificationAsync(string message)
    {
        return _hub.Clients.All.InvokeAsync("ReceiveMessage", message);
    }
}

Now you can inject the NotifyService into your class and send messages to all clients:

public class SomeClass
{
    private readonly NotifyService _service;

    public SomeClass(NotifyService service)
    {
        _service = service;
    }

    public Task Send(string message)
    {
        return _service.SendNotificationAsync(message);
    }
}

Answer 2

Simple inject the hubcontext into the class where you use the hubcontext.

Details you will find there:

Call SignalR Core Hub method from Controller

Answer 3

There are now official Microsoft Docs for the SignalR HubContext that answer your question https://docs.microsoft.com/en-us/aspnet/core/signalr/hubcontext?view=aspnetcore-2.1

But yes, as others have pointed out, you need to get an instance of IHubContext via dependency injection to access hub methods outside of the hub.