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?

Solution 1

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>();
     }
 .....

Solution 2

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

Solution 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.

Solution 4

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!

Solution 5

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>();

View more solutions

Comments

[Jakub Wisniewski]

This used to work in RC1 but does not work in RC2 (I get error) - do you know how to fix it?

[stibay]

How can you find the connManager somewhere else? Don't you have to inject or refrence it somehow since its not static?

[Bill Shihara]

As of the latest build, 0.0.2-alpha1-21709, this technique no longer works. I create a static variable for IConnectionManager in the startup class. When it is referenced in another class, the IHubContext is available but hub.Clients.All.SendMessage("foo") does not send a message to the clients.

[SHM]

hi, where did you get these information. i could not find docs after hours of searching. thanks..

[Andrew Nikolin]

Hi! Can you please post an example of how do you register HubContext class in IoC container?

[Suren]

@AndrewNikolin, not need to register HubContext. just introduce your Hub in Configure method. app.UseSignalR(routes => { routes.MapHub<LiveHub>("live"); }); l think by services.AddSignalR(); the HubContext would be registered automatically ...

[lenniep]

Thanks, that helped a lot. But how would I access the HubContext from outside a controller? Is there a way to call a hub method also from a static context?

[Suren]

@lenniep HubContext is reachable wherever IServiceProvider is available. you could get access to IServiceProvider in static class by some tip and tricks but it's not recommended at all.

[lenniep]

@Soren makes sense, thanks a lot. I will avoid this since I agree it's rather bad design. This has helped me as well: blog.ploeh.dk/2010/02/03/ServiceLocatorisanAnti-Pattern

[Glen Little]

@BillShihara - did you resolve the problem you mentioned here?

[santu47]

for me, connections is coming empty with this code snippet. Any help!!

[Niklas]

i was thinking as if i have to actually implement the IHubContext<MyHub> and then inject that using DI but then i realized i'd have to implement Clients and Groups etc, but reading the comments i realized that services.AddSignalR(); actually injects IHubContext<MyHub>by default so it saved me alot of frustration! documentation isn't clear on this to my knowledge. thanks to @Soren !

[Aaron]

Thank you so much. This was exactly what I needed to do to get SignalR working from background (hangfire) jobs

[William Jockusch]

@Soren that works unless the Hub has other dependencies, i.e. on MyApi.

[user2475096]

for .net 5 await _hubContext.Clients.All.SendAsync("yourmethod", yourparameters);

[Dharmesh Tailor]

I also wanted to use it within NServiceBus handler. End up following what @RenanStr suggested. works like a charm. But when you think about it, it's not something different to what you suggested "Static HubContext".