LiveDataSharedPreferences.kt

abstract class LiveDataSharedPreferences<T>(val sharedPreferences: SharedPreferences,
                                            val key: String,
                                            val default: T) : MutableLiveData<T>(), SharedPreferences.OnSharedPreferenceChangeListener {
    override fun onActive() {
        super.onActive()
        sharedPreferences.registerOnSharedPreferenceChangeListener(this)
    }

    override fun onInactive() {
        super.onInactive()
        sharedPreferences.unregisterOnSharedPreferenceChangeListener(this)
    }

    internal fun postWithouNotifyingChangeListeners(newValue: T) {
        sharedPreferences.unregisterOnSharedPreferenceChangeListener(this)
        postValue(newValue)
        sharedPreferences.registerOnSharedPreferenceChangeListener(this)
    }
}

class LiveDataSharedPreferencesInt(sharedPreferences: SharedPreferences, private val intKey: String,
                                   private val defaultInt: Int) : LiveDataSharedPreferences<Int>(
        sharedPreferences, intKey, defaultInt) {
    override fun onSharedPreferenceChanged(sharedPreferences: SharedPreferences, key: String) {
        if (intKey != key) {
            return
        }
        val newValue = sharedPreferences.getInt(intKey, defaultInt)
        postWithouNotifyingChangeListeners(newValue)
    }
}