AspNetCore.SignalR : Cannot start a connection that is not in the Initial state

Question

I have troubles to get my ASP.NET Core SignalR app working.

I have this server-side code :

public class PopcornHub : Hub
{
    private int Users;

    public async Task BroadcastNumberOfUsers(int nbUser)
    {
        await Clients.All.InvokeAsync("OnUserConnected", nbUser);
    }

    public override async Task OnConnectedAsync()
    {
        Users++;
        await BroadcastNumberOfUsers(Users);
        await base.OnConnectedAsync();
    }

    public override async Task OnDisconnectedAsync(Exception exception)
    {
        Users--;
        await BroadcastNumberOfUsers(Users);
        await base.OnDisconnectedAsync(exception);
    }
}

whose SignalR Hub service is configured as :

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddSignalR();
    ...
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    ...

    app.UseSignalR(routes =>
    {
        routes.MapHub<PopcornHub>("popcorn");
    });

    ...
}

In my client-side (WPF app), I have a service :

public class PopcornHubService : IPopcornHubService
{
    private readonly HubConnection _connection;

    public PopcornHubService()
    {
        _connection = new HubConnectionBuilder()
            .WithUrl($"{Utils.Constants.PopcornApi.Replace("/api", "/popcorn")}")
            .Build();
        _connection.On<int>("OnUserConnected", (message) =>
        {

        });
    }

    public async Task Start()
    {
        await _connection.StartAsync();
    }
}

My issue is that, when I call Start() method, I get the exception "Cannot start a connection that is not in the Initial state". The issue occurs either locally or in Azure.

The SignalR endpoint is fine but no connection can be established. What am I missing?

Answer 1

You seem to be trying to start a connection that has already been started. Also note that as of alpha2 the connection is not restartable - i.e. if it is stopped you cannot restart it - you need to create a new connection.

EDIT

In post alpha2 versions the connection will be restartable.