IoC (Ninject) and Factories

.net, c#, inversion-of-control, ioc-container, ninject

Solution

For your sample, you have a perfectly fine factory implementation and I wouldn't change anything.

However, I suspect that your KillerRobot and StandardRobot classes actually have dependencies of their own. I agree that you don't want to expose your IoC container to the RobotFactory.

One option is to use the ninject factory extension:

https://github.com/ninject/ninject.extensions.factory/wiki

It gives you two ways to inject factories - by interface, and by injecting a Func which returns an IRobot (or whatever).

Sample for interface based factory creation: https://github.com/ninject/ninject.extensions.factory/wiki/Factory-interface

Sample for func based: https://github.com/ninject/ninject.extensions.factory/wiki/Func

If you wanted, you could also do it by binding a func in your IoC Initialization code. Something like:

var factoryMethod = new Func<string, IRobot>(nameOfRobot =>
                        {
                            if (nameOfRobot == "Maximilian")
                            {
                                return _ninjectKernel.Get<KillerRobot>();
                            }
                            else
                            {
                                return _ninjectKernel.Get<StandardRobot>();
                            }

                        });
_ninjectKernel.Bind<Func<string, IRobot>>().ToConstant(factoryMethod);

Your navigation service could then look like:

    public class RobotNavigationService
    {
        public RobotNavigationService(Func<string, IRobot> robotFactory)
        {
            var killer = robotFactory("Maximilian");
            var standard = robotFactory("");
        }
    }

Of course, the problem with this approach is that you're writing factory methods right inside your IoC Initialization - perhaps not the best tradeoff...

The factory extension attempts to solve this by giving you several convention-based approaches - thus allowing you to retain normal DI chaining with the addition of context-sensitive dependencies.

Problem

If I have the following code: ``` public class RobotNavigationService : IRobotNavigationService { public RobotNavigationService(IRobotFactory robotFactory) { //... } } public class RobotFactory : IRobotFactory { public IRobot Create(string nameOfRobot) { if (name == "Maximilian") { return new KillerRobot(); } else { return new StandardRobot(); } } } ``` My question is what is the proper way to do Inversion of Control here? I don't want to add the KillerRobot and StandardRobot concretes to the Factory class do I? And I don't want to bring them in via a IoC.Get<> right? bc that would be Service Location not true IoC right? Is there a better way to approach the problem of switching the concrete at runtime?

Original source