A simple implementation of Event Bus using Kotlin

BusActivity.kt

package io.aoriani.simplebutterknife

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.TextView
import kotlin.reflect.KClass
import kotlin.reflect.KFunction
import kotlin.reflect.full.declaredMemberFunctions
import kotlin.reflect.jvm.jvmErasure

class BusActivity : AppCompatActivity() {

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

        EvenBus.register(this)

        setContentView(R.layout.activity_bus)
        findViewById<View>(R.id.button).setOnClickListener {
            EvenBus.post("Hi Earth!")
        }
    }


    @Suppress("unused")
    @Subscribe
    fun onEvent(event: String) {
        findViewById<TextView>(R.id.textView).text = event
    }
}


@Target(AnnotationTarget.FUNCTION)
@Retention(AnnotationRetention.RUNTIME)
annotation class Subscribe

object EvenBus {

    private val register = HashMap<KClass<*>, MutableList<Pair<Any, KFunction<*>>>>()

    fun register(subscriber: Any) {
        subscriber::class.declaredMemberFunctions
                .filter { it.annotations.any { it is Subscribe } && it.parameters.size == 2 && it.returnType.jvmErasure == Unit::class }
                .forEach {
                    val eventType = it.parameters[1].type.jvmErasure
                    if (eventType !in register) {
                        register[eventType] = arrayListOf()
                    }
                    register[eventType]?.add(subscriber to it)
                }
    }

    fun post(event: Any) {
        register[event::class]?.forEach {
            it.second.call(it.first, event)
        }
    }

}