Android Jetpack Adoption At Gett post - new way to write contract

Contract.kt

sealed class ProgressBarState
object ProgressBarShowState : ProgressBarState()
object ProgressBarHideState : ProgressBarState()


interface SomeScreenViewObservers {
  fun observeProgressBarState(lifecycle: Lifecycle, observer: (ProgressBarState) -> Unit)
}

interface IPresenter {
  fun startSomethingButtonClicked()
}