Cannot resolve scoped service 'FluentEmail.Core.Interfaces.ISender' from root provider.

I have .NET Core 2.1.2 application with IHostedService for sending email notifications. I register an email sending stuff:

    public class NotificationsFactory
    {
        public static void Register(IServiceCollection services, IAppSettings appSettings)
        {
            var client = new SmtpClient
            {
                Host = appSettings.EmailServerHost,
                Port = appSettings.EmailServerPort,
                UseDefaultCredentials = false,
                Credentials = new NetworkCredential(appSettings.EmailUser, appSettings.EmailPassword)
            };

            services
                .AddFluentEmail(appSettings.EmailFrom)
                .AddSmtpSender(client);

            services.AddSingleton<IEmailNotificationProvider, EmailNotificationProvider>();
        }
    }

then inject IFluentEmailFactory in my EmailNotificationProvider

public class EmailNotificationProvider : IEmailNotificationProvider
    {
        private readonly IFluentEmailFactory _emailFactory;

        public EmailNotificationProvider(IFluentEmailFactory emailFactory)
        {
            _emailFactory = emailFactory;
        }

        public async Task<bool> SendAsync(IOrder order)
        {
            try
            {
                var body = "Test body";

                await _emailFactory.Create()
                    .To(order.Company?.Email, "User")
                    .Subject($"New Order #{order.OrderId}")
                    .Body(body, true)
                    .SetFrom("[e-mail]", "Service")
                    .SendAsync();

                return true;
            }
            catch (Exception e)
            {
                return false;
            }
        }
    }

but get an error “Cannot resolve scoped service ‘FluentEmail.Core.Interfaces.ISender’ from root provider.” when creating new FluentEmail from factory.

What am I doing wrong?

[belidzs]

The problem is that IFluentEmail and IFluentEmailFactory cannot be injected in the constructor because when you use the provided AddFluentEmail() helper it creates the services as transient services instead of singleton services. Only singleton services can be injected through the constructor.

You can either manually add the service as a singleton (as mentioned above) or you can use the built methods and manually create a scope using the automatically injected IServiceProvider and explicitly request a dependency injection inside the created scope:

public class Worker : BackgroundService
{
    private readonly ILogger<Worker> _logger;
    private readonly IServiceProvider _serviceProvider;

    public Worker(ILogger<Worker> logger, IServiceProvider serviceProvider)
    {
        _logger = logger;
        _serviceProvider = serviceProvider;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        using (var scope = _serviceProvider.CreateScope())
        {
            var response = await scope.ServiceProvider.GetRequiredService<IFluentEmail>()
                .To("[e-mail]")
                .Subject(DateTime.Now.ToLongTimeString())
                .Body("test")
                .SendAsync(stoppingToken);
        }
    }
}

[okolobaxa]

Fixed by removing .AddSmtpSender(client) add adding services.AddSingleton<ISender>(x => new SmtpSender(client));

Is it a correct solution?