Sending Message in SignalR from the Web API - signalr

Question

I have created a hub in my Web API. It is very simple:
public class DashboardHub : Hub
{
public async Task SendMessage(InfoSummary infoSummary)
{
await Clients.All.SendAsync("ReceiveMessage", infoSummary);
}
}
I am trying to send a message to the Hub from a controller in the same Web API when data is updated.
I have seen 100 different answers, and nothing works. Basically my hub object in my controller is null, and I can't seem to get it instantiated.
private readonly IRepository _repo;
private readonly Helpers.Convert _convert;
private readonly CoreContext _context;
private readonly IMapper _mapper;
private readonly NotifyService _service;
private readonly DashboardHub _hub;
public MyController(IRepository repo,
CoreContext context,
IMapper mapper)
{
_convert = new Helpers.Convert(repo, mapper);
_repo = repo;
_context = context;
_mapper = mapper;
_hub = new DashboardHub();
_service = new NotifyService(_hub);
}
[HttpPost("updatestatus")]
public async Task<IActionResult> UpdateStatus(Header header) {
var returnVal = await _repo.ChangeStatus(header.HeaderId, header.Status);
headerSummary = _convert.ToReturnStatusHeader( await _repo.GetHeader(header.HeaderId));
// await _service.SendNotificationAsync(headerSummary);
await _hub.SendMessage(headerSummary);
return Ok(returnVal);
}
I have the
services.AddSignalR();
services.AddScoped(typeof(DashboardHub));
and
endpoints.MapHub<DashboardHub>("/Hubs/DashboardHub");
in the proper sections in the startup.cs file
I know I am missing something very small, but I would love to know what it is.
I have also tried creating a strongly typed hub, but that introduced even more problems.
Thanks in advance.

Answer 1

You have done there or four mistakes.
You don't need this line to be in your ConfigureServices method of Startup.cs. services.AddScoped(typeof(DashboardHub));
Remove it. Just keep services.AddSignalR();
Why are you using new key word, since .net core provide in-built dependency
injection service. Remove below lines.
_hub = new DashboardHub();
_service = new NotifyService(_hub);
Instead create a new interface INotifyService.cs for NotifyService.cs.
Register this service in ConfigureServices method of Startup.cs.
services.AddScoped<INotifyService, NotifyService>();
Your MyController.cs should be like below
Add this line.
using Microsoft.AspNetCore.SignalR;
private readonly IRepository _repo;
private readonly Helpers.Convert _convert;
private readonly CoreContext _context;
private readonly IMapper _mapper;
private readonly INotifyService _service;
private readonly IHubContext<DashboardHub> _hubContext
public MyController(IRepository repo, CoreContext context, IMapper mapper,INotifyService service,IHubContext<DashboardHub> hubContext)
{
_convert = new Helpers.Convert(repo, mapper);
_repo = repo;
_context = context;
_mapper = mapper;
_service = service;
_hubContext = hubContext;
}
[HttpPost("updatestatus")]
public async Task<IActionResult> UpdateStatus(Header header) {
var returnVal = await _repo.ChangeStatus(header.HeaderId, header.Status);
headerSummary = _convert.ToReturnStatusHeader( await _repo.GetHeader(header.HeaderId));
// await _service.SendNotificationAsync(headerSummary);
await hubContext.Clients.All.SendAsync("ReceiveMessage", headerSummary);
return Ok(returnVal);
}
Use same concept if you are sending messages inside your NotifyService.cs.

Answer 2

Well, I feel like a complete and utter newb. The fix is very simple. You must add the using statement telling the controller you want to use SignalR. OMG.. I am almost too embarrassed to put this up, but hope it will help someone else.
FIX:
using Microsoft.AspNetCore.SignalR;
:facepalm

Answer 3

What you could do is inject your hub using dependency injection in your controller. You can't just instanciate the hub in the controller like you are doing, and I would change it to a Singleton also.
services.AddSingleton(typeof(DashboardHub));
internal DashboardHub DashboardHub
{
get
{
return this.HttpContext.RequestServices.GetRequiredService<DashboardHub>();
}
}