Sending Message in SignalR from the Web API

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.

Solution

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.