Kotlin SharedPreferences delegate

prefs.kt

package cz.kinst.jakub.vmbk

import android.app.Activity
import android.app.Application
import android.app.Fragment
import android.app.Service
import android.arch.lifecycle.AndroidViewModel
import android.content.Context
import android.content.ContextWrapper
import android.content.SharedPreferences
import android.content.SharedPreferences.Editor
import android.preference.PreferenceManager
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

private inline fun <T> SharedPreferences.delegate(
        defaultValue: T, key: String? = null,
        crossinline getter: SharedPreferences.(String, T) -> T,
        crossinline setter: Editor.(String, T) -> Editor
) =
        object : ReadWriteProperty<Any, T> {
            override fun getValue(thisRef: Any, property: KProperty<*>): T =
                    getter(key ?: property.name, defaultValue)!!

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

fun SharedPreferences.int(def: Int = 0, key: String? = null): ReadWriteProperty<Any, Int> = delegate(def, key, SharedPreferences::getInt, Editor::putInt)

fun SharedPreferences.long(def: Long = 0, key: String? = null): ReadWriteProperty<Any, Long> = delegate(def, key, SharedPreferences::getLong, Editor::putLong)

fun SharedPreferences.float(def: Float = 0f, key: String? = null): ReadWriteProperty<Any, Float> = delegate(def, key, SharedPreferences::getFloat, Editor::putFloat)

fun SharedPreferences.boolean(def: Boolean = false, key: String? = null): ReadWriteProperty<Any, Boolean> = delegate(def, key, SharedPreferences::getBoolean, Editor::putBoolean)

fun SharedPreferences.stringSet(def: Set<String> = emptySet(), key: String? = null): ReadWriteProperty<Any, Set<String>> = delegate(def, key, SharedPreferences::getStringSet, Editor::putStringSet)

fun SharedPreferences.string(def: String = "", key: String? = null): ReadWriteProperty<Any, String> = delegate(def, key, SharedPreferences::getString, Editor::putString)


private fun sharedPrefs(context: Context, name: String?, mode: Int) =
        if (name == null)
            PreferenceManager.getDefaultSharedPreferences(context.applicationContext)
        else
            context.applicationContext.getSharedPreferences(name, mode)


fun AndroidViewModel.sharedPrefs(name: String? = null, mode: Int = ContextWrapper.MODE_PRIVATE) = sharedPrefs(getApplication(), name, mode)
fun Activity.sharedPrefs(name: String? = null, mode: Int = ContextWrapper.MODE_PRIVATE) = sharedPrefs(this, name, mode)
fun Fragment.sharedPrefs(name: String? = null, mode: Int = ContextWrapper.MODE_PRIVATE) = sharedPrefs(activity, name, mode)
fun Application.sharedPrefs(name: String? = null, mode: Int = ContextWrapper.MODE_PRIVATE) = sharedPrefs(this, name, mode)
fun Service.sharedPrefs(name: String? = null, mode: Int = ContextWrapper.MODE_PRIVATE) = sharedPrefs(this, name, mode)

usage.kt

// in Activity/Fragment/...
val savedId by sharedPrefs().string()