AutoClearedValue.kt

class AutoClearedValue<T : Any> : ReadWriteProperty<Fragment, T>, LifecycleObserver {
    private var _value: T? = null

    override fun getValue(thisRef: Fragment, property: KProperty<*>): T =
        _value ?: throw IllegalStateException("Trying to call an auto-cleared value outside of the view lifecycle.")

    override fun setValue(thisRef: Fragment, property: KProperty<*>, value: T) {
        thisRef.viewLifecycleOwner.lifecycle.removeObserver(this)
        _value = value
        thisRef.viewLifecycleOwner.lifecycle.addObserver(this)
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroy() {
        _value = null
    }
}