naive attempt at a state machine

asm.scala

import android.app.Activity
import android.os.Bundle

import ActivityStateMachine._

/**
  * @author pfnguyen
  */
trait ActivityStateMachine[T <: State[T]] extends Activity {

  private[this] var state: T = _
  override def onDestroy() = {
    super.onDestroy()
    state = state.transition(state.state, DESTROYED)
  }

  override def onCreate(savedInstanceState: Bundle) = {
    super.onCreate(savedInstanceState)
    state = state.transition(state.state, CREATED)
  }

  override def onStop() = {
    super.onStop()
    state = state.transition(state.state, STOPPED)
  }

  override def onStart() = {
    super.onStart()
    state = state.transition(state.state, STARTED)
  }

  override def onResume() = {
    super.onResume()
    state = state.transition(state.state, RESUMED)
  }

  override def onPause() = {
    super.onPause()
    state = state.transition(state.state, PAUSED)
  }
}

object ActivityStateMachine {
  sealed trait LifecycleState
  case object DESTROYED extends LifecycleState
  case object STOPPED extends LifecycleState
  case object PAUSED extends LifecycleState
  case object RESUMED extends LifecycleState
  case object STARTED extends LifecycleState
  case object CREATED extends LifecycleState
  trait State[T <: State[T]] {
    def state: LifecycleState
    def transition(prev: LifecycleState, next: LifecycleState): T
  }
}