Register multiple implementations with single interface

Question

Is there a way to register a single interface which is implemented by more than one concrete class using [simple-injector] and without using template interface?

say we have 2 classes MyClass1 and Myclass2 and both these classes are implementing IInterface1

Now using [simple-injector] we were not able to do this

container.Register<IInterface1, Myclass1>();
container.Register<IInterface1, Myclass2>();

converting existing interface to template interface is kinda a hard job on the existing codebase. Hoping there is some easier out there.

Steven · Accepted Answer · 2018-05-24 13:36:41Z

18

You can register multiple implementation of the same interface with using the RegisterCollection method (see documentation: Configuring a collection of instances to be returned)

So you need to write:

container.Collection.Register<IInterface1>(typeof(Myclass1), typeof(Myclass2));

And now Simple Injector can inject a collection of Interface1 implementation into your constructor, for example:

public class Foo
{
    public Foo(IEnumerable<IInterface1> interfaces)
    {
        //...
    }
}

Or you can explicitly resolve your IInterface1 implementations with GetAllInstances:

var myClasses = container.GetAllInstances<IInterface1>();

edited May 24, 2018 at 13:36

Steven

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answered Jul 26, 2013 at 19:47

nemesv

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4 Comments

Lester Over a year ago

Problem with SimpleInjector is, after registering multiple implementations for one interface, there is no way to specify which of the registered instances should be returned for a given interface. At your sample, you cannot specify to return an instance of class Myclass2 when asking for IInterface1. Other IoC containers like Ninject allows to "name" each registration for the same service (interface), so you can disambiguate later at resolution time.

Steven Over a year ago

@Lester: If you need this, make sure you're not violating the Liskov Substitution Principle if you need this. But either way, here's more information about using keyed registration in Simple Injector.

user2156081 Over a year ago

@nemesv what if we need one implementation at a time e.g. Shoper class constructor has ICreditCard interface. And 2 classes MasterCard and VisaCard classes implement ICreditCard. Shoper needs one class at a time. How to use IOC i this scenario?

Liam Over a year ago

Use a factory pattern to solve the above problem (comment above not the answer). So, create a factory, inject that and get that to return an implementation based on whatever logic you need.

Thiago Marcolino · Accepted Answer · 2019-08-20 21:46:16Z

0

I was faced with the same issue. I found a workaround, you can select the implementation depending on the consumer (I wish it were the other way around!). See the example below:

container.RegisterConditional<IInterface1, Myclass1>(
            c => c.Consumer.ImplementationType == typeof(Myclass2Service));
container.RegisterConditional<IInterface1, Myclass2>(
            c => c.Consumer.ImplementationType == typeof(Myclass2Service));

answered Aug 20, 2019 at 21:46

Thiago Marcolino

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