lifecycle callback managers

LifecycleController.kt

// lifecycle observers manager
class LifecycleController {

    private val observers = mutableListOf<LifecycleObserver>()
    private var state: LifecycleState = Unknown

    fun onInit() {
        observers.forEach { it.onInit() }
        state = Init
    }

    fun onVisible() {
        observers.forEach { it.onVisible() }
        state = Visible
    }

    fun onInvisible() {
        observers.forEach { it.onInvisible() }
        state = Invisible
    }

    fun onDeinit() {
        observers.forEach { it.onDeinit() }
        state = Deinit
    }
}

// lifecycle observer
interface LifecycleObserver {
    fun onInit() = Unit
    fun onVisible() = Unit
    fun onInvisible() = Unit
    fun onDeinit() = Unit
}