How to implement Multiple Notifiers with ASP.NET Boilerplate?

Question

I'm using ASP.NET Boilerplate (with .NET Core). I'm trying to implement notification system as mentioned in official doc under Multiple Notifiers, but I encountered:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

My question is not related to exception itself. I want to know if there are any pre-requests configuration or setting before I implement the example, or if my code misses something:

public class MessageAppService: AsyncCrudAppService<Message, MessageDto, long, PagedAndSortedResultRequestDto, CreateMessageDto, UpdateMessageDto, ReadMessageDto>, IRealTimeNotifier, ITransientDependency
{
    private readonly IRepository<Message, long> _repository;

    private readonly IDbContextProvider<MySystemDbContext> _dbContextProvider;
    private MySystemDbContext db => _dbContextProvider.GetDbContext();

    IHubContext<MyChatHub> _hubContext; // This for online chat

    private readonly IEmailSender _emailSender;
    private readonly UserManager _userManager;

    private readonly INotificationSubscriptionManager _notificationSubscriptionManager;

    public MessageAppService(
        IDbContextProvider<MySystemDbContext> dbContextProvider,
        IRepository<Message, long> repository, 
        IHubContext<MyChatHub> hubContext /* This for online chat */,
        INotificationSubscriptionManager notificationSubscriptionManager,
        IEmailSender emailSender,
        UserManager userManager
    ) : base(repository)
    {
        _repository = repository;
        _dbContextProvider = dbContextProvider;
        _hubContext = hubContext; // This for online chat 
        _notificationSubscriptionManager = notificationSubscriptionManager;
        _emailSender = emailSender;
        _userManager = userManager;
    }

    public override async Task<MessageDto> CreateAsync(CreateMessageDto input)
    {
        var test = await base.CreateAsync(input);
        UserNotification userNotifications = new UserNotification();
        userNotifications.UserId = 10010;
        //
        userNotifications.Notification.TenantId = AbpSession.TenantId;
        userNotifications.Notification.NotificationName = "test";

        UserNotification[] notificationList = new UserNotification[1];
        notificationList[0] = userNotifications;
        await SendNotificationsAsync(notificationList);
        return test;
    }

    public async Task SendNotificationsAsync(UserNotification[] userNotifications)
    {
        foreach (var userNotification in userNotifications)
        {
            if (userNotification.Notification.Data is MessageNotificationData data)
            {
                var user = await _userManager.GetUserByIdAsync(userNotification.UserId);

                _emailSender.Send(
                    to: "testg@gmail.com",
                    subject: "You have a new notification!",
                    body: data.Message,
                    isBodyHtml: true
                );
            }
        }
    }

    void IRealTimeNotifier.SendNotifications(UserNotification[] userNotifications)
    {
        throw new NotImplementedException();
    }
}

I've added below in PreInitialize() function in .Application module:

Configuration.Notifications.Notifiers.Add<MessageAppService>();

Update:

I know how to avoid this exception but I want to know if the steps that I've implemented in my code are enough to get the notification.

Update 2:

I've applied the code in the question mentioned by aaron. I got another exception:

WARN  2020-07-05 13:30:06,907 [9    ] fications.DefaultNotificationDistributer - System.Net.Mail.SmtpException: Failure sending mail.
 ---> System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (10061): No connection could be made because the target machine actively refused it. [::ffff:127.0.0.1]:25
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(IPEndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpClient.GetConnection()
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   --- End of inner exception stack trace ---
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Abp.Net.Mail.Smtp.SmtpEmailSender.SendEmail(MailMessage mail)
   at Abp.Net.Mail.EmailSenderBase.Send(MailMessage mail, Boolean normalize)
   at Abp.Net.Mail.EmailSenderBase.Send(String to, String subject, String body, Boolean isBodyHtml)
   at MySystem.ChatAppService.MessageAppService.SendNotificationsAsync(UserNotification[] userNotifications) in D:\WorkSpace\MySystem\aspnet-core\src\MySystem.Application\ChatAppService\MessageAppService.cs:line 172
   at Abp.Notifications.DefaultNotificationDistributer.NotifyAsync(UserNotification[] userNotifications)
System.Net.Mail.SmtpException: Failure sending mail.
 ---> System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (10061): No connection could be made because the target machine actively refused it. [::ffff:127.0.0.1]:25
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(IPEndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpClient.GetConnection()
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   --- End of inner exception stack trace ---
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Abp.Net.Mail.Smtp.SmtpEmailSender.SendEmail(MailMessage mail)
   at Abp.Net.Mail.EmailSenderBase.Send(MailMessage mail, Boolean normalize)
   at Abp.Net.Mail.EmailSenderBase.Send(String to, String subject, String body, Boolean isBodyHtml)
   at MySystem.ChatAppService.MessageAppService.SendNotificationsAsync(UserNotification[] userNotifications) in D:\WorkSpace\MySystem\aspnet-core\src\MySystem.Application\ChatAppService\MessageAppService.cs:line 172
   at Abp.Notifications.DefaultNotificationDistributer.NotifyAsync(UserNotification[] userNotifications)
WARN  2020-07-05 13:30:09,049 [10   ] fications.DefaultNotificationDistributer - System.Net.Mail.SmtpException: Failure sending mail.
 ---> System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (10061): No connection could be made because the target machine actively refused it. [::ffff:127.0.0.1]:25
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(IPEndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpClient.GetConnection()
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   --- End of inner exception stack trace ---
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Abp.Net.Mail.Smtp.SmtpEmailSender.SendEmail(MailMessage mail)
   at Abp.Net.Mail.EmailSenderBase.Send(MailMessage mail, Boolean normalize)
   at Abp.Net.Mail.EmailSenderBase.Send(String to, String subject, String body, Boolean isBodyHtml)
   at MySystem.ChatAppService.MessageAppService.SendNotificationsAsync(UserNotification[] userNotifications) in D:\WorkSpace\MySystem\aspnet-core\src\MySystem.Application\ChatAppService\MessageAppService.cs:line 172
   at Abp.Notifications.DefaultNotificationDistributer.NotifyAsync(UserNotification[] userNotifications)
System.Net.Mail.SmtpException: Failure sending mail.
 ---> System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (10061): No connection could be made because the target machine actively refused it. [::ffff:127.0.0.1]:25
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(IPEndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpClient.GetConnection()
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   --- End of inner exception stack trace ---
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Abp.Net.Mail.Smtp.SmtpEmailSender.SendEmail(MailMessage mail)
   at Abp.Net.Mail.EmailSenderBase.Send(MailMessage mail, Boolean normalize)
   at Abp.Net.Mail.EmailSenderBase.Send(String to, String subject, String body, Boolean isBodyHtml)
   at MySystem.ChatAppService.MessageAppService.SendNotificationsAsync(UserNotification[] userNotifications) in D:\WorkSpace\MySystem\aspnet-core\src\MySystem.Application\ChatAppService\MessageAppService.cs:line 172
   at Abp.Notifications.DefaultNotificationDistributer.NotifyAsync(UserNotification[] userNotifications)
ERROR 2020-07-05 13:30:28,176 [10   ] Mvc.ExceptionHandling.AbpExceptionFilter - Failure sending mail.
System.Net.Mail.SmtpException: Failure sending mail.
 ---> System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (10061): No connection could be made because the target machine actively refused it. [::ffff:127.0.0.1]:25
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(IPEndPoint remoteEP)
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
   at System.Net.Mail.SmtpClient.GetConnection()
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   --- End of inner exception stack trace ---
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Abp.Net.Mail.Smtp.SmtpEmailSender.SendEmail(MailMessage mail)
   at Abp.Net.Mail.EmailSenderBase.Send(MailMessage mail, Boolean normalize)
   at Abp.Net.Mail.EmailSenderBase.Send(String to, String subject, String body, Boolean isBodyHtml)
   at MySystem.ChatAppService.MessageAppService.CreateAsync(CreateMessageDto input) in D:\WorkSpace\MySystem\aspnet-core\src\MySystem.Application\ChatAppService\MessageAppService.cs:line 153
   at Abp.Authorization.AuthorizationInterceptor.InternalInterceptAsynchronous[TResult](IInvocation invocation)
   at Abp.Domain.Uow.UnitOfWorkInterceptor.InternalInterceptAsynchronous[TResult](IInvocation invocation)
   at Abp.Auditing.AuditingInterceptor.InternalInterceptAsynchronous[TResult](IInvocation invocation)
   at Abp.Runtime.Validation.Interception.ValidationInterceptor.InternalInterceptAsynchronous[TResult](IInvocation invocation)
   at lambda_method(Closure , Object )
   at Microsoft.Extensions.Internal.ObjectMethodExecutorAwaitable.Awaiter.GetResult()
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextExceptionFilterAsync>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)

Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Progman, Jul 05 '20 at 08:50
@Progman , No man it's not related to exception it self I want to know Beyond exception — 3202User, Jul 05 '20 at 08:53
Does this answer your question? [Building Notification Data for IRealTimeNotifier](https://stackoverflow.com/questions/56824021/building-notification-data-for-irealtimenotifier) — aaron, Jul 05 '20 at 09:54
@aaron I don't think so ,unless the Publish Notifications it's related to Multiple Notifiers ? — 3202User, Jul 05 '20 at 10:02
@aaron I've implmented your solution but another wxception occured ==> System.Net.Mail.SmtpException: Failure sending mail. — 3202User, Jul 05 '20 at 10:36
Please do not expand the scope of this question. Ask another question. — aaron, Jul 05 '20 at 10:40

score 0 · Answer 1 · answered Jul 05 '20 at 09:20

You do not show us enough information. What does UserNotification class contain? Is this your own class or ABP Framework's code?

The first obvious error I see is this piece of code:

UserNotification userNotifications = new UserNotification();
userNotifications.UserId = 10010;
//
userNotifications.Notification.TenantId = AbpSession.TenantId;
userNotifications.Notification.NotificationName = "test";

The Notification property does not seem to be initialized. I expected to see something like:

UserNotification userNotification = new UserNotification
{
   UserId = 10010,
   Notification = new Notification 
   {
     TenantId = AbpSession.TenantId,
     NotificationName = "test"
   }
};

UserNotification is ABP class and Notification part of UserNotification class . and I can't initialize Notification as you mentioned — 3202User, Jul 05 '20 at 09:25
https://aspnetboilerplate.com/api-docs/html/T_Abp_Notifications_UserNotification.htm — 3202User, Jul 05 '20 at 09:26

How to implement Multiple Notifiers with ASP.NET Boilerplate?

1 Answers1