SignalR getting disconnected while applying Dependency Injection

Question

I am new to SignalR and building a live chat by using .NET 5 and angular 13. While establishing the connection it is giving this error-- Connection closed with an error. NullReferenceException

After multiple debagging I found out what is the root cause of the problem. When I inject any dependency to my message hub. NullReferenceException error is happened. without dependency the connection is established properly.

here is my MessageHub.cs code (with dependency)

public class MessageHub : Hub
{
    private readonly IMessageRepository _messageRepository;
    private readonly IUserRepository _userRepository;

    public MessageHub(IMessageRepository messageRepository, IUserRepository userRepository)
    {
        _messageRepository = messageRepository;
        _userRepository = userRepository;
    }


    public override async Task OnConnectedAsync()
    {
        var httpContext = Context.GetHttpContext();

        var otherUser = httpContext.Request.Query["user"].ToString();

        var groupName = GetGroupName(Context.User.GetUsername(), otherUser);

        await Groups.AddToGroupAsync(Context.ConnectionId, groupName);
    }

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

}

Startup.cs (ConfigureServices)

   services.AddSignalR(e=>
        {
            e.EnableDetailedErrors = true;               
        });

Startup.cs (Configure)

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
            endpoints.MapHub<MessageHub>("hubs/message");
        });

I extremely need this dependency to complete my functionality. I got stack with this. If I remove the Dependency it works fine. I tried to find some solution from various sources but didn't work for me. if anyone help me. I will be really appreciate for this.

Answer 1

After doing some study, a solution I applied that worked for me. We Can Retrieve service object. so in startup.cs what I did given below

Startup.cs (ConfigureServices)

  //we can retrieve service object
  public static IServiceProvider serviceProvider;
  
  services.AddSignalR()
  services.AddScoped<IUserRepository, UserRepository>();
  services.AddScoped<IMessageRepository, MessageRepository>();

In my MessageHub.cs instead of using Dependency Injection I Retrieve Required Service and define it in the filed like below

MessageHub.cs

public class MessageHub : Hub
{
    private readonly IMessageRepository _messageRepository;
    private readonly IUserRepository _userRepository;

    public MessageHub()
    {
        _messageRepository = (IMessageRepository)Startup.serviceProvider.GetRequiredService(typeof(IMessageRepository));
        _userRepository = (IUserRepository)Startup.serviceProvider.GetRequiredService(typeof(IUserRepository));
    }

    // other code....
}

It worked for me. Now I can implement my necessary method from IRepository and SignalR also working properly.