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:0.2.0'

Getting Started

First of all, you need to write a module. A module gather your components definitions and allow 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, and override the context() function and use to 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 unlock the Koin DSL:

• provide { /* component definition */ } declare a component for your Module
• bind {/* compatible type */} bind a compatible type for provided definition
• get() inject a component dependency
• scope {/* scope class */} defineor 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 get 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 demo basics concepts:

• 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.