Companion code to https://medium.com/p/91c736276a52

example.kts

import android.app.Activity
import android.app.Application
import android.content.Context
import android.os.Bundle

// A Graph is just an interface that exposes your dependencies (like a Dagger 2 @Component).

interface Graph {

    val context: Context

    val analytics: Analytics

    val favoriteNumberRepo: FavoriteNumberRepo
}

// a custom application where you can store your graph
//
// the graph needs to be accessible from any
// activity/fragment/service/receiver,
// so store it in a custom Application

class CustomApplication : Application() {

    lateinit var graph: Graph

    override fun onCreate() {
        super.onCreate()

        // build the graph before onCreate
        // completes to guarantee availability
        graph = GraphBuilder()
            .context(this)
            .build()
    }
}

// base activity for all activities to extend
abstract class BaseActivity : Activity() {
    protected lateinit var graph: Graph
        private set

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // store a graph for easy access later
        graph = (application as CustomApplication).graph
    }
}

class FavoriteNumberActivity : BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // access dependencies on the graph
        graph.favoriteNumberRepo
            .loadFavoriteNumber("some user id")
    }
}

// a Repository class where you could load a user's favorite number
class FavoriteNumberRepo(
    private val analytics: Analytics
) {
    fun loadFavoriteNumber(userId: String): Int {
        analytics.track("favorite number loading")
        return 42
    }
}

class Analytics {
    fun track(eventName: String) {
        // ..
    }
}

class GraphBuilder {
    private lateinit var _context: Context
    private var analytics: Analytics? = null

    fun context(appContext: Context) = apply {
        _context = appContext
    }

    fun build(): Graph {
        require(::_context.isInitialized) {
            "context == null"
        }

        return GraphImpl(_context, analytics)
    }
}

// implementation of the Graph
class GraphImpl(
    override val context: Context,
    private val _analytics: Analytics? = null
) : Graph {
    override val analytics: Analytics
            by lazy {
                _analytics ?: Analytics()
            }
    override val favoriteNumberRepo: FavoriteNumberRepo
            by lazy {
                FavoriteNumberRepo(analytics)
            }
}

// base activity for all activities to extend
abstract class BaseActivity : Activity() {
    protected lateinit var graph: Graph
        private set

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // store a graph for easy access later
        graph = (application as CustomApplication).graph
    }
}

class FavoriteNumberActivity : BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // access dependencies on the graph
        graph.favoriteNumberRepo.loadFavoriteNumber("some user id")
    }
}