Insert Koin to make dependency injection

KOIN is a dependency injection framework that uses Kotlin and its functional power to get things done! No proxy/CGLib, No code generation, No introspection. Just functional Kotlin and DSL magic ;)

Setup

Check that you have jcenter repository. Add the following gradle dependency for your Android app:

compile 'org.koin:koin-android:0.2.1'

or if you need android-support classes:

compile 'org.koin:koin-android-support:0.2.1'

Getting Started

First of all, you need to write a module. A module gathers your components definitions and allows it to be loaded by Koin and injected in your application. Keep in mind, that injection by constructor is the default strategy targeted by Koin.

Writing a module

Write a class that extends AndroidModule, overrides the context() function and uses the declareContext function to define a context like below:

class MyModule : AndroidModule() {
    override fun context() =
        declareContext {
	    // declare dependency here ...
	    provide { createOkHttpClient() }
	}
    }
}

fun createOkHttpClient() : OkHttpClient { //create OkHttpClient ...}

Your context is provided by the context() function and described via the declareContext function. This unlocks the Koin DSL:

• provide { /* component definition */ } declares a component for your Module
• bind {/* compatible type */} bind a compatible type for provided definition
• get() inject a component dependency
• scope {/* scope class */} define or reuse a scope current module's definitions

AndroidModule also gives you the possibility to retrieve Android specific resources directly in your module context (ApplicationContext, Resources & Assets). e.g: Get an Android string in your module:

resources.getString(R.string.server_url)

Setup your Application

To start your module, you must build it:

val myContext = Koin().init(applicationInstance).build(MyModule())

This will return a KoinContext object. Koin proposes the KoinContextAware interface, to help define and bring your Koin context all over your app. Configure it like below:

class MainApplication : Application(), KoinContextAware {

     /**
     * Koin context
     */
    lateinit var context: KoinContext

    /**
     * KoinContextAware - Retrieve Koin Context
     */
    override fun getKoin(): KoinContext = context

    override fun onCreate() {
        super.onCreate()
        // insert Koin !
        context = Koin().init(this).build(MyModule()) 
        // ...
    }
}

By using KoinContextAware interface, you will be able to use the Koin Android extensions in your Android Application.

Don't forget to use the init() function to init Android context injection, else you won't be able to load your modules & extensions.

Start injecting

Once you have your Koin context, you can inject your components from anywhere (Application, Activity, Fragment) by using by inject<>() function:

class MainActivity : AppCompatActivity() {

    // inject my WeatherService 
    val weatherService by inject<WeatherService>()
    
    ...
}

That's it !

Sample App

You can find a complete sample app here: github sources

This sample shows the basic concepts of:

• A Module -- Module example to create okhttpClient, retrofit and web service component
• An Application -- Setup for loading module with Android application
• An Activity -- Inject WeatherService into MainActivity

Documentation

Check the wiki for complete documentation.

Articles

• Insert Koin for dependency injection
• Better dependency injection for Android

Contact & Support

Check the kotlin slack - #koin channel