How to resolve a MVC controller having a value type dependency with Simple Injector?

Question

I have the following controller:

public class MyController : Controller {
    private readonly IService service;
    private readonly int intDependency;

    public MyController(IService service, int intDependency) {
        this.service = service;
        this.intDependency = intDependency;
    }

    ...
}

Obviously resolution does not work, nor can I provide constructor parameter using a delegate, since this would end up with multiple constructor registration.

What is the correct way to proceed in this case? Is it generally uncorrect injecting value type as a dependency? Would it be a better practice to wrap the dependency behind an interface?

Answer 1

Is it generally uncorrect injecting value type as a dependency?

Indeed, as you can see there is no way for the injector to know which int it has to inject. Doesn't really make sense.

Would it be a better practice to wrap the dependency behind an interface?

Yes.

What is the correct way to proceed in this case?

You said it. Either an interface or a class.

Example:

public class MyConfig
{
    public int MyInt {get; set;}
}

And you could configure SimpleInjector like this:

container.RegisterSingleton(new MyConfig { MyInt = 42 });

and your controller would be:

public MyController(IService service, MyConfig config) { ...

Note: There is a way to inject primitive types : Primitive Dependencies with Simple Injector However, it's way easier and cleaner to just wrap the primitive in a class like my example.

Answer 2

Would it be a better practice to wrap the dependency behind an interface?

Yes, that would be the suggested solution. Value types aren't supported. Do instead of injecting the value directly, wrap it in a class and inject that.

Best practice to put an interface over the implementation but this is not necessary perse. Simple Injector doesn't matter. So this will work:

public class Values
{
    public Values(int value)
    { 
        this.SomeValue = value; 
    }

    public int SomeValue { get; }
}

// Register as
container.RegisterSingleton<Values>(() => new Values(1));

There are options, although a bit ugly and IMO not the way to go. These are described here