An error occurred when trying to create a controller of type 'XXXXController'. Make sure that the controller has a parameterless public constructor

Question

I have created a asp.net web api project and implemented the below HTTP GET method in AccountController and the related service method & repository method in AccountService & AccountRepository respectively.

// WEB API 
public class AccountController : ApiController
{
    private readonly IAccountService _accountService;

    public AccountController(IAccountService accountService)
    {
        _accountService = accountService;
    }

    [HttpGet, ActionName("UserProfile")]
    public JsonResult<decimal> GetUserSalary(int userID)
    {
        var account = _accountService.GetUserSalary(userID);
        if (account != null)
        {
            return Json(account.Salary);
        }
        return Json(0);
    }
}

Service / Business Layer

public interface IAccountService
{
    decimal GetUserSalary(int userId);
}

public class AccountService : IAccountService
{
    readonly IAccountRepository _accountRepository = new AccountRepository();

    public decimal GetUserSalary(int userId)
    {
        return _accountRepository.GetUserSalary(userId);
    }
}

Repository / Data Access Layer

public interface IAccountRepository
{
    decimal GetUserSalary(int userId);
}

public class AccountRepository : IAccountRepository
{
    public decimal GetUserSalary(int userId)
    {
        using (var db = new AccountEntities())
        {
            var account = (from b in db.UserAccounts where b.UserID == userId select b).FirstOrDefault();
            if (account != null)
            {
                return account.Salary;
            }
        }
        return 0;
    }
}

UnityConfig

public static class UnityConfig
{
    public static void RegisterComponents()
    {
        var container = new UnityContainer();
        container.RegisterType<IAccountService, AccountService>();
        container.RegisterType<IAccountRepository, AccountRepository>();
        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }
}

But when I invoke the API method GetUserSalary() I get an error saying

An error occurred when trying to create a controller of type 'AccountController'. Make sure that the controller has a parameterless public constructor.

Are you using Owin or classic asp.net flow i.e Startup.cs or Global.asax? — Marcus Höglund, Nov 09 '18 at 18:47

score 2 · Accepted Answer · answered Nov 09 '18 at 22:40

2

Check that you did not forget to register Unity IoC container itself:

if you use ASP.NET Framework it could be - Global.asax or Startap.cs (Owin) via UnityConfig.RegisterComponents() method.
if you use ASP.NET Core then in the Startup.cs file (I was unable to find official guides for its configuting)

answered Nov 09 '18 at 22:40

Rustam Ashurov

141
4

I have added UnityConfig.RegisterComponents() to Global.asax under Application_Start(). It worked. – Nov 10 '18 at 04:12

score -1 · Answer 2 · answered Nov 09 '18 at 18:25

-1

Your current constructor has parameters (or args if you prefer).

see:

public AccountController(IAccountService accountService)
{
    _accountService = accountService;
}

All you need to do is add a "Parameter-less Constructor" into the controller as well.

public AccountController()
{
}

Parameter-less constructors are usually above the ones that have params, though as far as I am aware this is only due to standards not any actual effect(s) it may cause.

There is also an already existing issue/question similar to this I will link below that may provide further details.

Make sure that the controller has a parameterless public constructor error

answered Nov 09 '18 at 18:25

Royal Kitsune

13
3

2

"All you need to do is add a "Parameter-less Constructor" into the controller as well." -> not if he depends on `IAccountService accountService`. He should check the DI registration – Peter Bons Nov 09 '18 at 19:06
@PeterBons How do we do that? Can you share a code? – Nov 10 '18 at 04:03
I have added above code. But it returns null exception for _accountService. – Nov 10 '18 at 04:04

An error occurred when trying to create a controller of type 'XXXXController'. Make sure that the controller has a parameterless public constructor

2 Answers2