Constructor with multiple arguments with Ninject

Question

I am tring to use Ninject as a IoC container but could not understand how to create an instance of a class that has more than 1 parameter in the constructor. Basically I have a service interface for authentication in a PCL library and its implementation in a WP8 project that receives in the constructor the cosumer key, secret and baseAddress:

//On PCL project
public interface IAuthorizationService {
 bool Authenticate();
}

//On WP8 Project
pubilc class MyAuthenticator : IAuthorizationService {
 public MyAuthenticator(string consumerKey, string consumerSecret, string baseAddress) { ... }
 public bool Authenticate() { ... }
}

Now I need to configure Ninject module so I can get an instance of IAuthorizationService. If my class had no constructors I would do:

internal class Module : NinjectModule {
 public override void Load() {
  this.Bind<IAuthorizationService>().To<MyAuthenticator>();
 }
}

If it had fixed values for the constructor I would do:

internal class Module : NinjectModule {
 public override void Load() {
  this.Bind<IAuthorizationService>().To<MyAuthenticator>().WithConstructorArgument( */* fixed argument here*/* );
 }
}

And to get an instance Module.Get<IAuthorizationService>()

But what if the constructor parameters cannot be resolved at compile time? How to pass the paramenters? How should the bind code be?

Edited to claryfy the question.

Why the downvote? should have at least commented so I could change the question... — Marcelo de Aguiar
it's probably because they felt that this question is easily answered by looking at the docs: github.com/ninject/ninject/wiki/… — BatteryBackupUnit
No, it is not! If you look at the docs all the constructor parameters are "injectable" too. My constructor has strings parameters. — Marcelo de Aguiar
to be precise, string is just another type which is just as "injectable" as any other type (interface, class). however, due to it's broad use it's not really suitable for injection. The same would be true for an ICurrency or ICultureInfo interface, too. Usually broadly-used types are passed as parameter or retrieved from a factory/provider (which is injected), p.Ex. ICurrencyProvider.GetUsersCurrency() or ICultureInfoProvider.GetCurrentUiCulture(). It quite the same concept as with entities: you usually don't inject an entity, rather you pass it along, or retrieve it from a repository. — BatteryBackupUnit
I upvoted this because I agree, the docs are garbage because they're tailored to work perfectly to the example they're showing. Concise real-world examples are much more favorable. — Brandon

BatteryBackupUnit BatteryBackupUnit · Accepted Answer · 2014-09-06T13:33:36

It's very easy. No matter how many constructor arguments, the binding stays the same:

Bind<IAuthorizationService>().To<MyAuthenticator>();

Let's say MyAuthenticator had a constructor with one parameter of type IFoo. All you got to do is tell ninject how it can resolve/create an IFoo. Again, very simple:

Bind<IFoo>().To<Foo>();

You don't need WithConstructorArgument ever, except in case you want to override the default behavior of ninject. Let's say MyAuthenticator has a parameter of type IFoo plus another parameter string seed which you want to configure specifically. All you'd need is:

Bind<IFoo>().To<Foo>();
Bind<IAuthorizationService>().To<MyAuthenticator>()
    .WithConstructorArgument("seed", "initialSeedValue");

no need to specify the value of the IFoo parameter!

Constructor with multiple arguments with Ninject

2 Answers