Call Signalr method from Controller .Net Core 2.1

Question

I am trying to call a method in the signalr Hub class from an (ASP.NET Core) MVC Controller, but I cannot find an example online that shows how to.

Note: There are lots of examples using older versions of signalr with the .Net Framework, but none that I can see that show how to do this in .Net Core.

I need to pass an id from the an MVC Action Result directly through to my Hub, without passing the id to the page, and then having to get a client connection back through to the hub.

public class ChatHub : Hub
{ 
    public async Task DoSomething(int id)
    {            
        //// Something in here.
    }
}



public class HomeController : Controller
{
    private readonly IHubContext<ChatHub> _hubContext;

    public HomeController(IHubContext<ChatHub> hubContext)
    {
        _hubContext = hubContext;
    }

    public async Task<ActionResult> Index(int id) 
    {

         //// Call the DoSomething method from here, passing the id across.
         await _hubContext.Clients.All.SendAsync("AddToGroup", groupId);
    }
}

Is there a way to do this please? (Or am I looking at this the wrong way, and is there a better way to achieve the same result?)

Update: If I pass the Id into the view, and then use JavaScript to call the Hub, this then calls the DoSomething method, so I can see it all hangs together correctly, but not when I try to call it in C#.

Answer 1

I think you're misunderstanding how it all works together (which is the same thing I did up until yesterday), the hub code is for the client-side script code to call back into and then action, whereas the IHubContext is used as the strongly typed methods that will be sent to the Client-side

Hub

// This class is used by the JavaScript Client to call into the .net core application.
public class ChatHub : Hub<IChatClient>
{

    public static ConcurrentDictionary<string, string> Connections = new ConcurrentDictionary<string, string>();

    // As an example, On connection save the user name with a link to the client Id for later user callback
    public override Task OnConnectedAsync()
    {
        var user = Context.User.Identity.Name;

        Connections.AddOrUpdate(this.Context.ConnectionId, user, (key, oldValue) => user);

        return base.OnConnectedAsync();
    }

    public override Task OnDisconnectedAsync(Exception exception)
    {
        // Do something on disconnect.
    }

    // Add other methods you want to be able to call from JavaScript side in here...
    public void SendMessage(int id, string message)
    {
        // Message doing stuff here.
    }
}

ChatClient Interface

// This provides strongly-typed methods that you'll have on the Client side but these don't exist on the server.
public interface IChatClient
{
    //So this method is a JS one not a .net one and will be called on the client(s)
    Task DoSomething(int id);

    Task NotificationUpdate(int id, string message);
}

Controller

public class HomeController : Controller
{
    private readonly IHubContext<ChatHub, IChatClient> _hubContext;

    public HomeController(IHubContext<ChatHub, IChatClient> hubContext)
    {
        _hubContext = hubContext;
    }

    public async Task<ActionResult> Index(int id) 
    {

         // This calls the method on the Client-side
         await _hubContext.Clients.All.DoSomething(id);
    }
}

Answer 2

You can use the IHubContext to do this:

public class HomeController : Controller
{
    private readonly IHubContext<ChatHub> _hubContext;

    public HomeController(IHubContext<ChatHub> hubContext)
    {
        _hubContext = hubContext;
    }

    public async Task<ActionResult> Index(int id) 
    {
         //// Call the DoSomething method from here, passing the id across.
         await _hubContext.Clients.All.SendAsync("DoSomething", id);
    }
}

Full docs and examples here.

Answer 3

I used the code here https://stackoverflow.com/a/53062957/6453193 for my HUB connection.

Since the js client-side code was not posted here. Just wanna share how I do it in js.

const connection = new signalR.HubConnectionBuilder()
    .withUrl("/chatHub")
    .configureLogging(signalR.LogLevel.Information)
    .withAutomaticReconnect()
    .build();

async function start() {
    try {
        await connection.start();
        console.log("SignalR Connected.");
    } catch (err) {
        console.log(err);
        setTimeout(start, 5000);
    }
};

connection.onclose(async () => {
    await start();
});

// Trigger if server-side code call it using NotificationUpdate
connection.on("NotificationUpdate", (message) => {
    alert(message);
});

// Start the connection.
start();

and my controller notifying the client-side

 await _hubContext.Clients.User(User.Identity.Name).NotificationUpdate($"This is an update");