Castle Windsor IoC Container Instantiation for multiple concrete types

Question

I am new to IoC and Castle Windsor.

The question is more related to IoC, but i just chose Castle as my weapon of choice.

I immediately ran into a problem that it seems impossible to construct the container from a config file or from a singleton.

The only way seeming to work for me is to use a Builder function that will construct the whole container each time and then let me specify the types, look at this example:

I have a view:

public interface IView
{
}

There are 2 concrete implementations of this view:

public class ConcreteViewA : IView
{
}

public class ConcreteViewB : IView
{
}

I have a controller that operates on the view:

public class Controller
{
    public Controller(IView view) { }
    public void Load() { }
}

I create a function that constructs my IoC container and register the common types, the only type i can register is my controller, as this is all that stays the same:

WindsorContainer BuildContainer()
    {
        var container = new WindsorContainer();
        container.Register(Component.For<Controller>().ImplementedBy<Controller>());
        return container;
    }

I have 2 (Root) entry points:

void RootMethod1()
    {
        var container = BuildContainer();
        container.Register(Component.For<IView>().ImplementedBy<ConcreteViewA>());
        var controller = container.Resolve<Controller>();
        controller.Load();
    }

    void RootMethod2()
    {
        var container = BuildContainer();
        container.Register(Component.For<IView>().ImplementedBy<ConcreteViewB>());
        var controller = container.Resolve<Controller>();
        controller.Load();
    }

As you can see I have to rebuild the container each time as i need to tell it what to use for IView for each of the context i am in. What if the Container is expensive to rebuild (Lots of types etc), how can I design this?

It this for an MVC application? If so, what does an instance of IView do? — Keith Bloom
I ask because in an ASP.Net application picking which view should be returned for an Action on a Controller is dealt with by the framework. — Keith Bloom
No this is a custom implementation for winforms. The Page Load event will create the controller/presenter which takes in a view which is the current instance (so it cannot be created) — Andre
I don't know how simplified this example is, but usually controller is tied to a specific view type. The problem you're having may be a design problem, not a framework-usage problem — Krzysztof Kozmic
I agree with you, and as you can see that my controller does depend on a type IView, but why must my controller care what the concrete implementation for IView is, the problem was simply telling the Container for each context what the concrete view is. All of the other types remain the same. I did simplify the example in order to get help, but imagine the controllers takes in a few dependencies, most of which remain the same and is easily handled by ioc except for the concrete view, which can change. — Andre

uttamkini uttamkini · Accepted Answer · 2011-10-11T17:09:29

From what I understand, you need two different instances of the Controller class (each one constructed with a different IView type). The easiest way to achieve this is to register two components with different names and different dependencies.

WindsorContainer BuildContainer()
{
    var container = new WindsorContainer();

        container.Register(Component.For<Controller>().Named("ControllerWithViewA")
                                                      .ImplementedBy<Controller>()
                                                      .DependsOn(Property.ForKey(typeof(IView))
                                                      .Is(typeof(ConcreteViewA)));
        container.Register(Component.For<Controller>().Named("ControllerWithViewB")
                                                     .ImplementedBy<Controller>()
                                                     .DependsOn(Property.ForKey(typeof(IView))
                                                     .Is(typeof(ConcreteViewB)));
    return container;
}

You can then ask for any controller as and when required.

void RootMethod1()
{
    var container = BuildContainer();
    var controller = container.Resolve<Controller>("ControllerWithViewA");
    controller.Load();
}

void RootMethod2()
{
   var controller = container.Resolve<Controller>("ControllerWithViewB");
   controller.Load();
}

A few more things to keep in mind when using DI

Build your container only once (Building it again and again is a waste of time and resources).
Be very sure which dependencies to inject and which not to. Overusing DI for everything can result in a bloated container which is a maintenance nightmare.
Be informed about the life cycle of your components (Singleton, Transient, per thread etc). Especially with Castle the default lifestyle is singleton which might create inconsistent behavior in a multi-threaded scenario.

Castle Windsor IoC Container Instantiation for multiple concrete types

2 Answers