NonConfigurationInstance.kt

/** Утилитарный файл. Может находиться в :common:util */
inline fun <reified T> ComponentActivity.nonConfigurationInstance(
  noinline instanceProducer: () -> T
) = NonConfigurationInstanceLazy(
  instanceProducer = instanceProducer,
  instanceHolder = viewModels()
)

inline fun <reified T> Fragment.nonConfigurationInstance(
  noinline instanceProducer: () -> T
) = NonConfigurationInstanceLazy(
  instanceProducer = instanceProducer,
  instanceHolder = viewModels()
)

class NonConfigurationInstanceHolder<T> : ViewModel() {
  var nonConfigurationInstance: T? = null
}

class NonConfigurationInstanceLazy<T>(
  private val instanceProducer: () -> T,
  private val instanceHolder: Lazy<NonConfigurationInstanceHolder<T>>
) : Lazy<T> {
  override val value: T
    get() = with(instanceHolder.value) {
      nonConfigurationInstance ?: instanceProducer().also { nonConfigurationInstance = it }
    }

  override fun isInitialized() = instanceHolder.isInitialized()
}