Invoking SignalR Hub not working for Asp.Net Core Web API

Question

I'm a newb to SignalR. I'm trying to set up a Asp.Net Core WebAPI so that other clients can connect to it using SignalR and get real-time data. My Hub class is:

public class TimeHub : Hub
{
    public async Task UpdateTime(string message)
    {
        await Clients.All.SendAsync("ReceiveMessage", message);
    }
}

I have a relay class as follows:

public class TimeRelay : ITimeRelay
{
    private readonly IHubContext<TimeHub> _timeHubContext;

    public TimeRelay(IHubContext<TimeHub> context)
    {

        _timeHubContext = context;
        Task.Factory.StartNew(async () =>
        {
            while (true)
            {
                await context.Clients.All.SendAsync("UpdateTime", DateTime.Now.ToShortDateString());
                Thread.Sleep(2000);
            }
        });
    }
}

Startup class:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

    services.AddSignalR();
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseDeveloperExceptionPage();

    app.UseHttpsRedirection();

    app.UseSignalR((x) =>
    {
        x.MapHub<TimeHub>("/timeHub");
    });
    app.UseMvc();
}

The client is a console application and the code is:

class Program
{    
    static Action<string> OnReceivedAction = OnReceived;

    static void Main(string[] args)
    {
        Connect();
        Console.ReadLine();
    }

    private static async void Connect()
    {
        var hubConnectionBuilder = new HubConnectionBuilder();

        var hubConnection = hubConnectionBuilder.WithUrl("http://localhost:60211/timeHub").Build();

        await hubConnection.StartAsync();

        var on = hubConnection.On("ReceiveMessage", OnReceivedAction);

        Console.ReadLine();    
        on.Dispose();
        await hubConnection.StopAsync();
    }

    static void OnReceived(string message)
    {
        System.Console.WriteLine($"{message}");
    }
}

I tried debugging the application. The client got connected to the TimeHub succesfully. The no of connections in Clients.All changed from 0 to 1, when the client got connected. But, when await context.Clients.All.SendAsync("UpdateTime", DateTime.Now.ToShortDateString()); is executed, the UpdateTime function in TimeHub is not getting executed and the client is not getting any message.

I tried using "UpdateTime", "SendMessage", and "ReceiveMessage" as method in Clients.All.SendAsync in TimeRelay class. Nothing worked. Could someone point out my mistake in this.

Answer 1

I got it to work and thought I will answer it here. Thanks @TaoZhou for the tip.

My mistake was sending "UpdateTime" from server and waiting on "ReceiveMessage" at the client.

Ideally the code should look like the following:

SignalR Server:
await context.Clients.All.SendAsync("UpdateTime", DateTime.Now.ToShortDateString());

SignalR Client:
var on = hubConnection.On("UpdateTime", OnReceivedAction);

In this case any message send from the server would be received at the client instantly.
Please refer the code provided in the question for more info.