Is it possible to use Ninject Factory Extensions' ToFactory method with open generics?

Question

I'm building on a previously answered question in which ICar implementations are bound using Ninject Conventions Extensions and a custom IBindingGenerator, and the ICarFactory interface is bound using the Ninject Factory Extensions' ToFactory() method and a custom instance provider.

I'm trying to refactor so that I can bind and make use of a IVehicleFactory<T>, where T is constrained to ICar, rather than the previous ICarFactory. This way, I can specify the vehicle I want in the generic type parameter, instead of passing in the name of the vehicle type in the factory's CreateCar() method.

Is it possible to bind open generic interfaces using the ToFactory() technique?

I have a feeling that I'm barking up the wrong tree, but when I was specifying an ICar type by its name, it seemed like the natural evolution to specify the ICar type itself as a generic type parameter...

Here's the test that currently fails:

[Fact]
public void A_Generic_Vehicle_Factory_Creates_A_Car_Whose_Type_Equals_Factory_Method_Generic_Type_Argument()
{
    using (StandardKernel kernel = new StandardKernel())
    {
        // arrange
        kernel.Bind(typeof(IVehicleFactory<>))
            .ToFactory(() => new UseFirstGenericTypeArgumentInstanceProvider());

        kernel.Bind(
            scanner => scanner
                           .FromThisAssembly()
                           .SelectAllClasses()
                           .InheritedFrom<ICar>()
                           .BindWith(new BaseTypeBindingGenerator<ICar>()));
        IVehicleFactory<Mercedes> factory 
            = kernel.Get<IVehicleFactory<Mercedes>>();

        // act
        var car = factory.CreateVehicle();

        // assert
        Assert.IsType<Mercedes>(car);
    }
}

And the InvalidCastException thrown:

System.InvalidCastException was unhandled by user code
  Message=Unable to cast object of type 'Castle.Proxies.ObjectProxy' to type 'IVehicleFactory`1[Mercedes]'.
  Source=System.Core
  StackTrace:
       at System.Linq.Enumerable.<CastIterator>d__b1`1.MoveNext()
       at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
       at Ninject.ResolutionExtensions.Get[T](IResolutionRoot root, IParameter[] parameters) in c:\Projects\Ninject\ninject\src\Ninject\Syntax\ResolutionExtensions.cs:line 37
       at NinjectFactoryTests.A_Generic_Vehicle_Factory_Creates_A_Car_Whose_Type_Name_Equals_Factory_Method_String_Argument() in C:\Programming\Ninject.Extensions.Conventions.Tests\NinjectFactoryTests.cs:line 37
  InnerException: 

And the factory interface:

public interface IVehicleFactory<T> where T : ICar
{
    T CreateVehicle();
}

And the custom instance provider, whose breakpoints I can't even get the debugger to stop on, so I really don't know what's going on in there:

public class UseFirstGenericTypeArgumentInstanceProvider : StandardInstanceProvider
{
    protected override string GetName(MethodInfo methodInfo, object[] arguments)
    {
        var genericTypeArguments = methodInfo.GetGenericArguments();
        var genericMethodDefinition = methodInfo.GetGenericMethodDefinition();
        var g = genericMethodDefinition.MakeGenericMethod(genericTypeArguments.First());
        return g.MemberType.GetType().Name;
    }

    protected override ConstructorArgument[] GetConstructorArguments(MethodInfo methodInfo, object[] arguments)
    {
        return base.GetConstructorArguments(methodInfo, arguments).Skip(1).ToArray();
    }
}

EDIT 1 - Change IVehicleFactory signature and custom instance provider

Here's I've changed the IVehicleFactory signature to use a generic Create<T>() method, and explicitly bound Mercedes to itself.

public interface IVehicleFactory
{
    T CreateVehicle<T>() where T : ICar;
}

And the new custom instance provider which returns the name of the first generic type parameter:

public class UseFirstGenericTypeArgumentInstanceProvider : StandardInstanceProvider
{
    protected override string GetName(MethodInfo methodInfo, object[] arguments)
    {
        var genericTypeArguments = methodInfo.GetGenericArguments();
        return genericTypeArguments[0].Name;
    }
}

Here's the new test, still not passing:

[Fact]
public void A_Generic_Vehicle_Factory_Creates_A_Car_Whose_Type_Name_Equals_Factory_Method_String_Argument()
{
    using (StandardKernel kernel = new StandardKernel())
    {
        // arrange
        kernel.Bind<IVehicleFactory>()
            .ToFactory(() => new UseFirstGenericTypeArgumentInstanceProvider())
            .InSingletonScope();
        kernel.Bind<Mercedes>().ToSelf();
        IVehicleFactory factory = kernel.Get<IVehicleFactory>();

        // act
        var car = factory.CreateVehicle<Mercedes>();

        // assert
        Assert.IsType<Mercedes>(car);
    }
}

}

A Ninject.ActivationException is thrown:

Ninject.ActivationException: Error activating Mercedes
No matching bindings are available, and the type is not self-bindable.
Activation path:
  1) Request for Mercedes

I don't know why it can't find the Mercedes class, since I explicitly self-bound it. Can you spot what I'm doing wrong?

Answer 1

Use generic methods:

public interface IVehicleFactory
{
    CreateVehicle<T>();
}