Question

I am learning asp.net mvc3. one example I found online is to show me how to use IOC.

            public class HomeController : Controller
            {
                private IHelloService _service;
                public HomeController():this(new HelloService())
                {}

                public HomeController(IHelloService service)
                {
                    _service = service;
                }
            }

there are two constructors in this example. I understand the second one. the first one I understand what that for, but to me, it seems like extra code, you will never need it.

can someone please explain to me whats the point to add the first constructor.

                public HomeController():this(new HelloService())
                {}

Answer 1

When the MVC Framework instantiates a controller, it uses the default (parameter-less) constructor.

By default, you are injecting a concrete IHelloService implementation. This will be used when a user navigates to the action.

Unit Tests would use the overload and pass in the mock IHelloService implementation rather than calling the default constructor.