Dependency Injection Constructor Conflict - asp.net-mvc

Question

I have a controller and I want to use Dependency Injection with constructor,this is my code
private readonly IHomeService _iHomeService;
public HomeController(IHomeService iHomeService)
{
_iHomeService = iHomeService;
}
public HomeController()
{
}
When I remove Constructor without any parameter(Second Constructor),I see this error :
No parameterless constructor defined
and When I use Constructor without any parameter,I see my private field is null(_iHomeService = null) because program use constructor without parameter.
How can I resolve this problem for Dependency Injection?

Answer 1

Well, to do dependency injection youll need to either use a framework or use controller factory .
try ninject
public class HomeController : Controller
{
private readonly IWelcomeMessageService welcomeMessageService;
public HomeController(IWelcomeMessageService welcomeMessageService)
{
this.welcomeMessageService = welcomeMessageService;
}
public void Index()
{
ViewModel.Message = this.welcomeMessageService.TodaysWelcomeMessage;
return View();
}
}
public class WelcomeMessageServiceModule : NinjectModule
{
public override void Load()
{
this.Bind<IWelcomeMessageService>().To<WelcomeMessageService>();
}
}
The framework will take control on the controller instance creation and pass the constractor params

Answer 2

It sounds like you are expecting, automatically, the HomeService class to be instantiated and injected into the Controller.
Using an IoC framework like Ninject or StructureMap will do that for you - once you've set it up.
If you don't want to use an IoC framework, you'll need to manually instantiate the HomeService in your constructor.

Answer 3

ASP.NET uses a ControllerFactory to instantiate your controllers on-demand. This class requires that your controller has a parameterless constructor that it can use to create an instance of it.
You'll need to use a dependency injection framework to create your controllers and inject the required dependencies. ASP.NET has some dependency injection capability, but I understand that it is flawed. I suggest using Castle Windsor to manage your dependency injection. It integrates very well with ASP.NET, and there's a tutorial on integrating it here.
If you go down this route, you'd end up with an installer for your controllers and service:
public class Installer : IWindsorInstaller
{
public void Install(IWindsorContainer container, IConfigurationStore store)
{
container.Register(Classes.FromThisAssembly().BasedOn<IController>().LifestyleTransient());
container.Register(Component.For<IHomeService>.ImplementedBy<HomeService>());
}
}
..and a new ControllerFactory to create them:
public class WindsorControllerFactory : DefaultControllerFactory
{
private readonly IKernel _kernel;
public WindsorControllerFactory(IKernel kernel)
{
_kernel = kernel;
}
public override void ReleaseController(IController controller)
{
_kernel.ReleaseComponent(controller);
}
protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
{
if (controllerType == null)
{
throw new HttpException(404, string.Format("The controller for path '{0}' could not be found.", requestContext.HttpContext.Request.Path));
}
return (IController) _kernel.Resolve(controllerType);
}
}
Finally, you'd create a container and set a new controller factory:
var container = new WindsorContainer().Install(new Installer());
var controllerFactory = new WindsorControllerFactory(_container.Kernel);
ControllerBuilder.Current.SetControllerFactory(controllerFactory);
You could also use Ninject or StructureMap.