Android Kotlin - SharedPreferences property delegates

SharedPreferencesNullableProperty.kt

import android.content.SharedPreferences
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KFunction3
import kotlin.reflect.KProperty

@Suppress("UNCHECKED_CAST")
inline fun <reified T> sharedPreferences(sharedPreferences: SharedPreferences, key: String): SharedPreferencesNullableProperty<T> =
        when (T::class) {
            Boolean::class -> SharedPreferencesNullableProperty(sharedPreferences, key, false,
                    SharedPreferences::getBoolean, SharedPreferences.Editor::putBoolean)

            Float::class -> SharedPreferencesNullableProperty(sharedPreferences, key, 0f,
                    SharedPreferences::getFloat, SharedPreferences.Editor::putFloat)

            Int::class -> SharedPreferencesNullableProperty(sharedPreferences, key, 0,
                    SharedPreferences::getInt, SharedPreferences.Editor::putInt)

            Long::class -> SharedPreferencesNullableProperty(sharedPreferences, key, 0L,
                    SharedPreferences::getLong, SharedPreferences.Editor::putLong)

            String::class -> SharedPreferencesNullableProperty(sharedPreferences, key, null,
                    SharedPreferences::getString, SharedPreferences.Editor::putString)

            Set::class -> SharedPreferencesNullableProperty(sharedPreferences, key, null,
                    SharedPreferences::getStringSet, SharedPreferences.Editor::putStringSet)

            else -> throw IllegalStateException("Illegal property type: ${T::class}")
        } as SharedPreferencesNullableProperty<T>

class SharedPreferencesNullableProperty<T>(
        private val sharedPreferences: SharedPreferences,
        val key: String,
        val defaultValue: T,
        val getValue: KFunction3<SharedPreferences, String, T, T>,
        val setValue: KFunction3<SharedPreferences.Editor, String, T, SharedPreferences.Editor>)
    : ReadWriteProperty<Any, T?> {

    override fun getValue(thisRef: Any, property: KProperty<*>): T? =
            if (!sharedPreferences.contains(key)) {
                null
            } else {
                getValue(sharedPreferences, key, defaultValue)
            }


    override fun setValue(thisRef: Any, property: KProperty<*>, value: T?) =
            sharedPreferences.edit().apply {
                if (value == null) {
                    remove(key)
                } else {
                    setValue(sharedPreferences.edit(), key, value).apply()
                }
            }.apply()
}

SharedPreferencesProperty.kt

import android.content.SharedPreferences
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KFunction3
import kotlin.reflect.KProperty

@Suppress("UNCHECKED_CAST")
fun <T> sharedPreferences(sharedPreferences: SharedPreferences, key: String, defaultValue: T): SharedPreferencesProperty<T> =
        when (defaultValue) {
            is Boolean -> SharedPreferencesProperty(sharedPreferences, key, defaultValue,
                    SharedPreferences::getBoolean, SharedPreferences.Editor::putBoolean)

            is Float -> SharedPreferencesProperty(sharedPreferences, key, defaultValue,
                    SharedPreferences::getFloat, SharedPreferences.Editor::putFloat)

            is Int -> SharedPreferencesProperty(sharedPreferences, key, defaultValue,
                    SharedPreferences::getInt, SharedPreferences.Editor::putInt)

            is Long -> SharedPreferencesProperty(sharedPreferences, key, defaultValue,
                    SharedPreferences::getLong, SharedPreferences.Editor::putLong)

            is String -> SharedPreferencesProperty(sharedPreferences, key, defaultValue,
                    SharedPreferences::getString, SharedPreferences.Editor::putString)

            is Set<*> -> SharedPreferencesProperty(sharedPreferences, key, defaultValue as Set<String>,
                    SharedPreferences::getStringSet, SharedPreferences.Editor::putStringSet)

            else -> throw IllegalStateException("Illegal property type: ${(defaultValue as Any).javaClass}")
        } as SharedPreferencesProperty<T>

open class SharedPreferencesProperty<T>(
        private val sharedPreferences: SharedPreferences,
        val key: String,
        val defaultValue: T,
        val getValue: KFunction3<SharedPreferences, String, T, T>,
        val setValue: KFunction3<SharedPreferences.Editor, String, T, SharedPreferences.Editor>)
    : ReadWriteProperty<Any, T> {

    override fun getValue(thisRef: Any, property: KProperty<*>): T =
            getValue(sharedPreferences, key, defaultValue)

    override fun setValue(thisRef: Any, property: KProperty<*>, value: T) =
            setValue(sharedPreferences.edit(), key, value).apply()
}