CODEWITHSUNDEEP
c#dependency-injectionninjectinversion-of-control
Ruudjah
Ruudjah

Reputation: 847

Ninject auto resolve by generic type

We use Ninject for Dependency Injection. We are designing our code using our free-form-interpreted DDD, where a domain object is an IThing.

In the following code, how to get an IThingControl using an IThing instance?

interface IThing {}
class Thing : IThing {}

interface IThingControl<T> where T:IThing {}
class ThingControl<Thing> {}

class Module : NinjectModule {
    public override void Load() {
        Bind<IThingControl<Thing>>().To<ThingControl>();
    }
}

class SomewhereInCode {
    void AddControls() {
        List<IThing> things = new List<IThing> {
            new Thing()
        };
        foreach (IThing thing in things) {
            IThingControl<IThing> control = _kernel.Get(); // <----- eh?
            this.Controls.Add(control);
        }
    }
}

Upvotes: 1

Views: 1520

Answers (2)

TheFastCat
TheFastCat

Reputation: 3464

I would revisit your design if you aim to retrieve a generic controller from an interface to its domain object.

Ninject does not play well with generic domain types as interfaces. This is due to the incovariance of generic types: Ninject - Managing Inconvariance of generic types?

Upvotes: 0

qujck
qujck

Reputation: 14580

You can get an instance using MakeGenericType (here) but you can't cast it to IThingControl<IThing>

interface IThing { }
class Thing1 : IThing { }
class Thing2 : IThing { }
interface IThingControl<T> where T : IThing { }
class ThingControl<Thing> { }

class Module : NinjectModule {
    public override void Load()
    {
        Bind(typeof(IThingControl<>)).To(typeof(ThingControl<>));
    }
}

[TestFixture]
public class SomewhereInCode
{
    [Test]
    public void AddControls()
    {
        IKernel kernel = new StandardKernel(new Module());
        List<IThing> things = new List<IThing> { new Thing1(), new Thing2() };
        Type baseType = typeof(IThingControl<>);

        foreach (IThing thing in things)
        {
            Type type = baseType.MakeGenericType(thing.GetType());
            dynamic control = kernel.Get(type);
            Assert.That(
                control is IThingControl<IThing>,
                Is.False);
        }
    }
}

Upvotes: 3

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