Cannot use SendGrid

Question

I'm trying to use SendGrid for send email with my ASP.NET Core application, so I configured it in the following way:

Inside the ConfigureServices method I added a Singleton and a configuration to access to SendGrid API:

services.AddSingleton<IEmailSender, IEmailSender>();
services.Configure<AuthMessageSenderOptions>(Configuration);

the class AuthMessageSenderOptions is part of the software configuration:

public class AuthMessageSenderOptions
{
    public string SendGridUser { get; set; }
    public string SendGridKey { get; set; }
}

this class manage the SendGrid username and the secret key.

I created a service class with implement the IEmailSender interface, this is the implementation:

public class EmailSender : IEmailSender
{
    public AuthMessageSenderOptions Options { get; }

    public EmailSender(IOptions<AuthMessageSenderOptions> optionsAccessor)
    {
        Options = optionsAccessor.Value;
    }

    public Task SendEmailAsync(string email, string subject, string message)
    {
        return Execute(Options.SendGridKey, subject, message, email);
    }

    public Task Execute(string apiKey, string subject, string message, string email)
    {
        var client = new SendGridClient(apiKey);

        var msg = new SendGridMessage()
        {
            From = new EmailAddress("foo@gmail.com", "Foo"),
            Subject = subject,
            PlainTextContent = message,
            HtmlContent = message
        };

        msg.AddTo(new EmailAddress(email));

        msg.TrackingSettings = new TrackingSettings
        {
            ClickTracking = new ClickTracking { Enable = false }
        };

        return client.SendEmailAsync(msg);
    }
}

Then in my Account controller (which is used for perform the registration and login), I injected the IEmailSender service to the constructor:

public class AccountController : Controller
{
   private readonly IEmailSender _emailSender;

   public AccountController(IEmailSender emailSender)
   {
       _emailSender = emailSender;
   }

when I start the application I get this error:

System.ArgumentException: 'Cannot instantiate implementation type 'Microsoft.AspNetCore.Identity.UI.Services.IEmailSender' for service type 'Microsoft.AspNetCore.Identity.UI.Services.IEmailSender'.'

inside the Program class, in particular on this line:

CreateWebHostBuilder(args).Build().Run();

this is the full Program class:

public class Program
{
    public static void Main(string[] args)
    {
        CreateWebHostBuilder(args).Build().Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>();
}

What I did wrong?

I'm learning ASP.NET Core so, sorry if I did something stupid, I followed this doc to implement the SendGrid logic.

Answer 1

services.AddSingleton<IEmailSender, IEmailSender>();

should specify the implementation in the second template argument:

services.AddSingleton<IEmailSender, EmailSender>();