How to get SignalR Hub Context in a ASP.NET Core?

Question

I'm trying to get the context for a hub using the following:

var hubContext = GlobalHost.ConnectionManager.GetHubContext<SomeHub>();

The problem is that GlobalHost is not defined. I see it is part of the SignalR.Core dll. At the moment, I have the following in my project .json file, under dependencies:

"Microsoft.AspNet.SignalR.Server": "3.0.0-*"

If I add the latest available version of Core:

"Microsoft.AspNet.SignalR.Server": "3.0.0-*",
"Microsoft.AspNet.SignalR.Core" :  "2.1.2"

I get a whole bunch of errors because server and core are conflicting. If I change them to both use version "3.0.0-*", all the conflicts go away, but GlobalHost cannot be found. If I remove Server, and just user Core version 2.1.2 then GlobalHost works, but all the other things needing Server, obviously do not.

Any ideas?

Answer 1

IConnectionManager does not exist any more in SignalR for ASP.Net Core.
I've been using HubContext for getting access to a hub.

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

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

    public void SendToAll(string message)
    {
        _hubContext.Clients.All.InvokeAsync("Send", message);
    }
}

I'm using .net core 2.0.0 and SignalR 1.0.0-alpha1-final

Answer 2

Microsoft.AspNet.SignalR.Infrastructure.IConnectionManager is a DI injected service through which you can get the hub context...For example:

using Microsoft.AspNet.SignalR;
using Microsoft.AspNet.SignalR.Infrastructure;
using Microsoft.AspNet.Mvc;

public class TestController : Controller
{
     private IHubContext testHub;

     public TestController(IConnectionManager connectionManager)
     {
         testHub = connectionManager.GetHubContext<TestHub>();
     }
 .....

Answer 3

To use the hub in a backgroud service, in addition to controllers, you must use the IHostedService interface and get the hub by DI.

public class MyBackgroundService : IHostedService, IDisposable
{
    public static IHubContext<NotifierHub> HubContext;

    public MyBackgroundService(IHubContext<NotifierHub> hubContext)
    {
        HubContext = hubContext;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        //TODO: your start logic, some timers, singletons, etc
        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        //TODO: your stop logic
        return Task.CompletedTask;
    }

    public void Dispose()
    {
    }
}

Then you can call your hub from anywhere in your code from HubContext static field:

MyBackgroundService.HubContext.Clients.All.SendAsync("UpdateData", myData).Wait();

Learn more about IHostedService: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-2.1

You can create and start a timer in MyBackgroundService and call the hub in ElapsedEvent.

Answer 4

I added some code to my Startup.cs to grab reference to the ConnectionManager which you can then use to do a GetHubContext at anytime from anywhere in your code. Similar to Nimo's answer but a little different, maybe simpler.

services.AddSignalR(options =>
{
    options.Hubs.EnableDetailedErrors = true;
});

var provider = services.BuildServiceProvider();

//Hold on to the reference to the connectionManager
var connManager = provider.GetService(typeof(IConnectionManager)) as IConnectionManager;

//Use it somewhere else
var hub = connManager.GetHubContext<SignalHub>();

Answer 5

I needed to be able to access the Hub Context from outside the app request thread - because I was subscribing to NServicebus messages, and needed to be able to trigger a client function when I received a message.

Here's how I got it sorted:

public static IServiceProvider __serviceProvider;

then during startup configuration

app.UseServices(services =>
        {
            __serviceProvider = new ServiceCollection()
            .BuildServiceProvider(CallContextServiceLocator.Locator.ServiceProvider);
        });

Then anywhere else in the vNext asp.net application (any other thread)

 var manager = Startup.__serviceProvider.GetRequiredService<IConnectionManager>();
            var hub = manager.GetHubContext<ChatHub>();

Hope this helps!

Answer 6

I'm looking at SignalR source code and it seems that IHubContext is registered as a singleton.

Which means you get the same instance whenever you access it.

Which means you can simply save it in a static var and use it from whatever.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHubContext<MyHub> hubContext)
{
    _staticVar = hubContext;
}

But be warned - it's an anti-pattern.