Unable to resolve service for type while attempting to activate

Question

I have one file Repository.cs that contains an interface and its implementation like so:

public interface IRepository

{
    IEnumerable

        

Answer 1

A method like this needs to be added to your Startup:

    // This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    //...

    // Add application services.
    services.AddTransient<IRepository, MemoryRepository>();

    //..
}

Services should be registered before used.

UPDATE: If you do not want to use DI on your application, just create and instance of MemoryRepository on the constructor of HomeController, like this:

public class HomeController : Controller
    {
        private IRepository repository;

        public HomeController()
        {
            repository = new MemoryRepository();
        }

        public IActionResult Index()
        {
            return View(repository.Cities);
        }

    }

Answer 2

Other answers are CORRECT, however I was spinning up a new asp.net core 2.1.x project and got this error.

Ended up being a typo by ME.

So in my Controller instead of Correctly using the Interface like this

public HomeController(IApplicationRepository applicationRepository)
{
    _applicationRepository = applicationRepository;
}

My typo had me using ApplicationRepository instead of ApplicationRepository Notice below, and so with NO ERRORS spotting the missing "I" was fun :/

public HomeController(ApplicationRepository applicationRepository)
{
    _applicationRepository = applicationRepository;
}

Thus the controller was not resolving the DI...

Answer 3

This may not be helpful for your code sample but in my case the same error was a result of a circular dependency.

Answer 4

You have to add your implementation to DI (Dependeny Injection) section. For .Net Core Mvc, it would be like this:

 public void ConfigureServices(IServiceCollection services)
 {
   services.AddDbContext<ApplicationDbContext>(options =>
    options.UseInMemoryDatabase()
   );
   services.AddScoped<IRepository, MemoRepostory>();

 }

Answer 5

We are getting this error in Entity frame work core database first approach. I followed below steps and error got resolvedenter code here

Step 1: Check Your context class constructor should be like this

public partial class ZPHSContext : DbContext
{
    public ZPHSContext(DbContextOptions<ZPHSContext> dbContextOptions):base(dbContextOptions)
    {
    }
}

Step 2: In Startup file

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();
    services.AddDbContext<ZPHSContext>(options => options.UseSqlServer(Configuration.GetConnectionString("BloggingDatabase")));
}

Step 3: Connection string in appsettings

"ConnectionStrings": {
    "BloggingDatabase": "Server=Server=****;Database=ZPHSS;Trusted_Connection=True;"
}

Step 4: Remove default code in OnConfiguring method in context class

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
}

Answer 6

you have to register your repository like this

services.AddSingleton<IRepository, MemoryRepository>();