Get Hub Context in SignalR Core from within another object

Question

I am using Microsoft.AspNetCore.SignalR (latest release) and would like to get the hub context from within another object that\'s not a Controller.

Answer 1

So after looking over this example from the accepted answer, I didn't quite get where he was going, so I tried a few things and I think I got what he was saying. So, for folks who have this issue in the future, I want to change that example to a fully working example.

So we are going to create a "Shared Methods", like in the example:

using Microsoft.AspNetCore.SignalR;
using System.Threading.Tasks;

namespace YouDontNeedToKnow.Core.Main.Hubs
{
    internal class HubMethods<THub> where THub : Hub
    {
        private readonly IHubContext<THub> _hubContext;

        public HubMethods(IHubContext<THub> hubContext)
        {
            _hubContext = hubContext;
        }

        public Task InvokeOnGroupAsync(string groupName, string method, params object[] args) =>
            _hubContext.Clients.Group(groupName).InvokeAsync(method, args);

        public Task InvokeOnAllAsync(string method, params object[] args) =>
            _hubContext.Clients.All.InvokeAsync(method, args);

        public Task AddConnectionIdToGroupAsync(string connectionId, string groupName) =>
            _hubContext.Groups.AddAsync(connectionId, groupName);

        // ...
    }
}

Then, in your Hub object, you add a constructor, like so:

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.SignalR;

namespace YouDontNeedToKnow.Core.Main.Hubs
{
    internal class MyHub : Hub
    {
        public static string HubName => "myHub";

        private readonly HubMethods<MyHub> _hubMethods;

        public PlayerServicesHub(HubMethods<MyHub> hubMethods)
        {
            _hubMethods = hubMethods;
        }

        public override Task OnConnectedAsync()
        {
            return base.OnConnectedAsync();
        }
    }
}

In your Startup.cs, you inject the shared class like so:

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<HubMethods<MyHub>>();
    services.AddSignalR();
    services.AddMvc();
}

This still works as it normally would:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IServiceProvider sp)
{
    app.UseDefaultFiles();
    app.UseStaticFiles();
    app.UseSignalR(routes =>
    {
        routes.MapHub<MyHub>(MyHub.HubName);
    });
    app.UseMvc();
    // This is just an example line of how you can get the hub with context:
    var myHub = sp.GetService<HubMethods<MyHub>>();
}

Answer 2

Just set IHubContext<MyHub> hubContext on calling-side constructor.

I would recommend using .net core default DI container mechanism, not creating static property.

Please refer to How do I get a reference to a Hub?

public class MyHub : Hub
{
}

public class CallingSideClass
{
    private readonly IHubContext<MyHub> _hubContext;

    public CallingSideClass(IHubContext<MyHub> hubContext)
    {
        _hubContext = hubContext;
    }

    public async Task FooMethod(...)
    {
        await _hubContext.Clients.All.InvokeAsync(...);
    }
}

public class Startup
{...
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSignalR();
        services.AddScoped<CallingSideClass>();
    }
    ... 
}