States

CollectionUtils.kt

fun Map<String, Parcelable>.toBundle(): Bundle {
    val output = Bundle()
    for (key in keys) {
        output.putParcelable(key, this[key])
    }
    return output
}

fun <T : Parcelable>Bundle.toMap(c: Class<T>): ArrayMap<String, T> {
    val output = ArrayMap<String, T>()
    for (key in keySet()) {
        output[key] = c.cast(getParcelable(key))
    }
    return output
}

StatePreferences.kt

class StatePreferences @Inject constructor(private val preferences: SharedPreferences) {

    fun removeScrollPosition() {
        preferences.edit().remove(SCROLL_POSITION).apply()
    }

    fun restoreScrollPosition(): Int {
        return preferences.getInt(SCROLL_POSITION, RecyclerView.NO_POSITION)
    }

    fun saveScrollPosition(scrollPosition: Int) {
        if (scrollPosition == RecyclerView.NO_POSITION) {
            preferences.edit().remove(SCROLL_POSITION).apply()
        } else {
            preferences.edit().putInt(SCROLL_POSITION, scrollPosition).apply()
        }
    }

    companion object {
        private const val KEY_ = "state_"
        private const val VIDEO_LIST_ ="${KEY_}video_list_"
        private const val SCROLL_POSITION = "${VIDEO_LIST_}scroll_position"
    }
}

StatesActivity.kt

abstract class StatesActivity: BaseActivity() {
    var states = ArrayMap<String, Parcelable>()

    fun saveState(key: String, state: Parcelable) {
        states[key] = state
    }
    fun restoreState(key: String): Parcelable? = states[key]

    override fun onSaveInstanceState(outState: Bundle?) {
        super.onSaveInstanceState(outState)
        outState?.putBundle(KEY_STATES, states.toBundle())
    }

    override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
        super.onRestoreInstanceState(savedInstanceState)
        states = savedInstanceState?.getBundle(KEY_STATES)?.toMap(Parcelable::class.java)?: states
    }

    companion object {
        const val KEY_STATES = "states"
    }
}