Calling SignalR functions outside of Hub Class - dependency-injection

Question

I am are trying to get an instance of a Hub Class to call front-end methods from the backend from a class outside of the Hub class.
I am using IHostLifeTime that has a register function that will be running in the background while the server is running in a while loop.
There will be events in the while loop that will trigger signalR to send a message to the client.
Question: How am I supposed to get access to the hub and send a message to the client inside of my manager class in the ApplicationReady() function?
TestHub.cs:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SignalR;
namespace SignalREventHandle
{
public class TestHub : Hub
{
public async Task SendMessage(string user, string message)
{
Console.WriteLine($"user: {user} message:{message}");
await Clients.All.SendAsync("ReceiveMessage", user, message);
}
}
}
Startup.cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.SignalR;
using System.Threading;
namespace SignalREventHandle
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddRazorPages();
services.AddSignalR();
}
// This method gets called by the runtime. Use this method to configure the HTTP request //pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHostApplicationLifetime lifetime, IHubContext<TestHub> hubContext)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Error");
}
lifetime.ApplicationStarted.Register(OnAppStarted);
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapRazorPages();
endpoints.MapHub<TestHub>("/testHub");
});
}
public async void OnAppStarted()
{
//Get Singleton Instance of Manager and then start the application
var manager = Manager.Instance;
manager.ApplicationReady();
}
}
}
Manager.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.SignalR;
namespace SignalREventHandle
{
public class Manager
{
private bool _isServerRunning;
/// <summary>
/// Instance of class to implement Singleton
/// </summary>
private static readonly Manager _instance = new();
/// <summary>
/// Getter for Class instance
/// </summary>
public static Manager Instance
{
get => _instance;
}
public async void ApplicationReady()
{
var task = Task.Run(() =>
{
_isServerRunning = true;
while (_isServerRunning)
{
// Want to Send Message to Client with SignalR here
Thread.Sleep(10000);
}
});
}
}
}

Answer 1

In ASP.NET 4.x SignalR use GlobalHost to provide access to the IHubContext:
public static async Task SendMessage(string user, string message)
{
Console.WriteLine($"user: {user} message: {message}");
// Get an instance of IHubContext from GlobalHost
var hubContext = GlobalHost.ConnectionManager.GetHubContext<ChatHub>();
await hubContext.Clients.All.SendAsync("ReceiveMessage", user, message);
}
In ASP.NET Core SignalR, you can access an instance of IHubContext from the web host.
Program.cs
public class Program
{
public static IHost WebHost;
public static void Main(string[] args)
{
WebHost = CreateHostBuilder(args).Build();
WebHost.Run();
}
...
}
Then:
public static async Task SendMessage(string user, string message)
{
Console.WriteLine($"user: {user} message: {message}");
// Get an instance of IHubContext from IHost
var hubContext = Program.WebHost.Services.GetService(typeof(IHubContext<ChatHub>)) as IHubContext<ChatHub>;
await hubContext.Clients.All.SendAsync("ReceiveMessage", user, message);
}
Documentation:
https://learn.microsoft.com/en-us/aspnet/core/signalr/hubcontext?view=aspnetcore-5.0
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