Unable to resolve service for type xxx while attempting to activate yyy [duplicate]

Question

I have an asp.net core 2.1 project with Identity enabled, however after making certain changes to seed users I run into some issues.

The error I get when I click Register as a new user is

InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.UI.Services.IEmailSender' while attempting to activate 'namespace.Website.Main.Areas.Identity.Pages.Account.RegisterModel'.

In the Register.cshtml.cs class I see that IEmailSender is injected but I have made no alterations to this and cannot understand why this error is happening? Please help

Startup.cs

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.Configure<CookiePolicyOptions>(options =>
        {
            // This lambda determines whether user consent for non-essential cookies is needed for a given request.
            options.CheckConsentNeeded = context => true;
            options.MinimumSameSitePolicy = SameSiteMode.None;
        });
        services.AddIdentity<IdentityUser, IdentityRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>();
        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection")));
        services.AddHttpClient();

        services.AddHttpClient<IExceptionServiceClient, ExceptionServiceClient>();
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
    }
}

RolesConfig

public static class RolesConfig
{
    public static async Task InitialiseAsync(ApplicationDbContext context, IServiceProvider serviceProvider)
    {
        var roleManager = serviceProvider.GetRequiredService<RoleManager<IdentityRole>>();
        string[] roleNames = { "Admin", "Report", "Search" };
        foreach (var roleName in roleNames)
        {
            var roleExist = await roleManager.RoleExistsAsync(roleName);
            if (!roleExist)
                await roleManager.CreateAsync(new IdentityRole(roleName));
        }
    }
}

Register.cshtml.cs

public class RegisterModel : PageModel
{
    private readonly SignInManager<IdentityUser> _signInManager;
    private readonly UserManager<IdentityUser> _userManager;
    private readonly ILogger<RegisterModel> _logger;
    private readonly IEmailSender _emailSender;

    public RegisterModel(
        UserManager<IdentityUser> userManager,
        SignInManager<IdentityUser> signInManager,
        ILogger<RegisterModel> logger,
        IEmailSender emailSender)
    {
        _userManager = userManager;
        _signInManager = signInManager;
        _logger = logger;
        _emailSender = emailSender;
    }

    [BindProperty]
    public InputModel Input { get; set; }

    public string ReturnUrl { get; set; }

    public class InputModel
    {
        [Required]
        [EmailAddress]
        [Display(Name = "Email")]
        public string Email { get; set; }

        [Required]
        [StringLength(100, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 6)]
        [DataType(DataType.Password)]
        [Display(Name = "Password")]
        public string Password { get; set; }

        [DataType(DataType.Password)]
        [Display(Name = "Confirm password")]
        [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
        public string ConfirmPassword { get; set; }
    }

    public void OnGet(string returnUrl = null)
    {
        ReturnUrl = returnUrl;
    }

    public async Task<IActionResult> OnPostAsync(string returnUrl = null)
    {
        returnUrl = returnUrl ?? Url.Content("~/");
        if (ModelState.IsValid)
        {
            var user = new IdentityUser { UserName = Input.Email, Email = Input.Email };
            var result = await _userManager.CreateAsync(user, Input.Password);
            if (result.Succeeded)
            {
                _logger.LogInformation("User created a new account with password.");

                var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
                var callbackUrl = Url.Page(
                    "/Account/ConfirmEmail",
                    pageHandler: null,
                    values: new { userId = user.Id, code = code },
                    protocol: Request.Scheme);

                await _emailSender.SendEmailAsync(Input.Email, "Confirm your email",
                    $"Please confirm your account by <a href='{HtmlEncoder.Default.Encode(callbackUrl)}'>clicking here</a>.");

                await _signInManager.SignInAsync(user, isPersistent: false);
                return LocalRedirect(returnUrl);
            }
            foreach (var error in result.Errors)
            {
                ModelState.AddModelError(string.Empty, error.Description);
            }
        }

        // If we got this far, something failed, redisplay form
        return Page();
    }
}

Any help is much appreciated! Thank you

Answer 1

Problem is you are using IEmailSender thorough constructor Dependency Injection in RegisterModel but you did not register the IEmailSender to ASP.NET Core DI container. So to register IEmailSender, add the following line to your ConfigureServices method of the Startup class:

services.AddScoped<IEmailSender,EmailSender>();

Now problem should go away.