activity_with_tasks.kt

package LifecycleDemo

import java.util.*


/**
 * The purpose of this pattern is to give the ability to group actions that belong together
 * but that have to be executed at a different point of the android activity lifecycle
 *
 * This extension function creates a delegate for all children of LifecycleActivity

 * For comparaison puropose, you can find the standard android version here
https://gist.github.com/jmfayard/4740cba818a998323f9b
 */
fun  LifecycleActivity.activityTask(action : (event : ActivityEvent) -> Unit)
        = lazy { ActivityTask(action) }

/** parameter is one of **/
enum class ActivityEvent {
    OnCreate, OnStart, OnResume, OnPause, OnStop, OnDestroy
}

/** Your activity class must extends LifecycleActivity **/
class MyActivity : LifecycleActivity() {

    override fun onCreate() {
        super.onCreate()
    }

    /**
     * Tasks that will be called in LifecycleActivity's onCreate onStart onResume onPause onStop onDestroy
     * You must override this function
     */
    override fun listOfLifecycleTasks() = listOf(firstTask, secondTask, thirdTask)

    // Do something depending on the ActivityEvent parameter
    val firstTask by activityTask { event ->
        when (event) {
            ActivityEvent.OnStart -> println("SDK XYZ needs to do something in onStart()")
            ActivityEvent.OnStop ->  println("SDK XYZ needs to do something in Stop()")
            else -> {}
        }
    }

    // activityTask is lazy so you don't have to worry about using variables not initialized in onCreate
    val secondTask by activityTask { event ->
        when (event) {
            ActivityEvent.OnCreate ->  hockeySdkStartMonitoring()
            ActivityEvent.OnDestroy -> hockeySdkStopMonitoring()
            else -> {}

        }
    }

    val thirdTask by activityTask { event ->
        when (event) {
            ActivityEvent.OnResume -> println("Do this in onPause()")
            ActivityEvent.OnPause  -> println("Do taht in onResume()")
            else -> {}
        }
    }



    private fun hockeySdkStopMonitoring() {
        println("HockeySdk : start monigoring")
    }

    private fun hockeySdkStartMonitoring() {
        println("HockeySdk : stop monigoring")
    }


}


/**
 * Store your task
 */
class ActivityTask(val action : (event : ActivityEvent) -> Unit)


/**
 * The lifecycle-aware base clss
 */
open class LifecycleActivity : Activity() {

    /** Used by the children classes to tell LifecycleActivity
     * which ActivityTask should be run
     */
    open fun listOfLifecycleTasks(): List<ActivityTask> = emptyList<ActivityTask>()


    override fun onCreate() {
        super.onCreate()
        runAllActivityTasks(ActivityEvent.OnCreate)

    }


    override fun onDestroy() {
        super.onDestroy()
        runAllActivityTasks(event = ActivityEvent.OnDestroy)

    }

    override fun onPause() {
        super.onPause()
        runAllActivityTasks(event = ActivityEvent.OnPause)

    }

    override fun onResume() {
        super.onResume()
        runAllActivityTasks(event = ActivityEvent.OnResume)

    }

    override fun onStart() {
        super.onStart()
        runAllActivityTasks(event = ActivityEvent.OnStart)

    }

    override fun onStop() {
        super.onStop()
        runAllActivityTasks(event = ActivityEvent.OnStop)

    }


    private fun runAllActivityTasks(event: ActivityEvent) {
        listOfLifecycleTasks().forEach { task -> run {
            task.action(event)
        }}

    }
}


// fake emulation of android activities
open class Activity {

    open fun onCreate() { }
    open fun onDestroy() { }

    open fun onStart() { }
    open fun onStop() { }

    open fun onResume() { }
    open fun onPause() { }
}