How to provide the base class in Koin?

Question

For example I the following classes:

abstract class BaseClass()

class SpecificClass : BaseClass()

Now, I want to provide SpecificClass through koin dependency inject but I also want to provide the base class BaseClass in the same graph.

To be clear I want to do something like:

class Someclass {
    ...
    private specificClass: SpecificClass by inject()
    ...
}

class Someclass {
    ...
    private baseClass: BaseClass by inject() 
    // where this BaseClass is just the the same instace of the SpecificClass in the dependency graph
    ...
}

How do I do my module to do this? How can I inject the implementation instance to the baseClass reference?

score 7 · Accepted Answer · answered Jul 10 '19 at 06:24

You can do it using Koin in 2 ways

Methodn 1

You can create dependencies for both of them like this

single {
    SpecificClass()
}

single<BaseClass> {
    get<SpecificClass>()
}

In this way, whenever you inject an instance, it will get injected accordingly

Method 2

You can make use of named dependencies like this

single("BaseClassImpl") {
        SpecificClass()
    }

And when you want to inject it, provide key for that dependency like this:

class Someclass {
    ...
    private specificClass: SpecificClass by inject("BaseClassImpl")
    ...
}

class Someclass {
    ...
    private baseClass: BaseClass by inject("BaseClassImpl") 
    // where this BaseClass is just the the same instace of the SpecificClass in the dependency graph
    ...
}

score 0 · Answer 2 · answered Jul 09 '19 at 12:04

You can't inject abstract classes.

In order to inject a class, it must be instantiable and abstract classes are not.

To inject SpecificClass with Koin you need to create a module:

val appModule = module {
    single {
        SpecificClass()
    }
}

Initialize it in your application class:

class MyApplication : Application() {
  override fun onCreate(){
    super.onCreate()
    // start Koin!
    startKoin {
      // declare used Android context
      androidContext(this@MyApplication)
      // declare modules
      modules(appModule)
    }
  } 
}

And use the inject delegation in your activity/fragment

class MyActivity() : AppCompatActivity() {

    val specificClass : SpecificClass by inject()
}

yeah i understand that but what if I also want to provide `SpecificClass` as `BaseClass`. — Archie G. Quiñones, Jul 10 '19 at 02:22

How to provide the base class in Koin?

2 Answers2