Constructor DI + Unity 2.0 + issue with resolving dependency - asp.net-mvc-3

Question

Controller:
public class HomeController : Controller
{
IEmployeeTask _employeeTask;
public HomeController()
{
_employeeTask = new UnityContainer().Resolve<IEmployeeTask>();
}
public HomeController(IEmployeeTask employeeTask)
{
_employeeTask = employeeTask;
}
public ActionResult Index()
{
ViewBag.Message = "Welcome to ASP.NET MVC!";
return View();
}
public ActionResult GetAndDisplayEmployee()
{
return View();
}
[HttpPost]
public ActionResult GetAndDisplayEmployee(int empid)
{
return View(_employeeTask.GetEmployeeModelFromService(empid));
}
}
Global.asax.cs:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
var container = new UnityContainer();
container.RegisterType<IEmployeeModelMap, EmployeeModelMap>();
container.RegisterType<IEmployeeService, EmployeeService>();
container.RegisterType<IEmployeeTask, EmployeeTask>();
container.RegisterType<IEmployee, Employee>();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}
Unity Dependency Resolver:
public class UnityDependencyResolver : IDependencyResolver
{
readonly IUnityContainer _container;
public UnityDependencyResolver(IUnityContainer container)
{
this._container = container;
}
public object GetService(Type serviceType)
{
try
{
return _container.Resolve(serviceType);
}
catch
{
return null;
}
}
public IEnumerable<object> GetServices(Type serviceType)
{
try
{
return _container.ResolveAll(serviceType);
}
catch
{
return new List<object>();
}
}
}
Employee Task class:
public class EmployeeTask: IEmployeeTask
{
IEmployeeService _employeeService;
IEmployeeModelMap _employeeModelMap;
public EmployeeTask(IEmployeeService employeeService, IEmployeeModelMap employeeModelMap)
{
_employeeService = employeeService;
_employeeModelMap = employeeModelMap;
}
public EmployeeViewModel GetEmployeeModelFromService(int empId)
{
return _employeeModelMap.ToModel(_employeeService.GetEmployeeFromEntities(empId));
}
}
Now, i have used unity 2.0 application block. Tried to resolve the dependency of the controller using unity with out using Custom Controller factory.
I am stuck with below error.
The current type, DataProviderInfrastructure.IEmployeeTask, is an
interface and cannot be constructed. Are you missing a type mapping?

Answer 1

I don't use Unity, but my guess would be that it attempts to use your parameterless constructor where you try to resolve the dependency. Creating this constructor is very very wrong. First - it defeats the purpose of having dependency injection and second - you create new container inside - which will be empty so it obviously can't resolve any dependencies. Try removing this from your code:
public HomeController()
{
_employeeTask = new UnityContainer().Resolve<IEmployeeTask>();
}