Android SharedPreferences helper class for Kotlin. Easy-to-use delegated properties, automatic database creation, and listening for property changes.

README.md

Usage

Wrapper class for SharedPreferences, leveraging the awesome delegate syntax in Kotlin.

Call Preferences.init(context) in your Application class.

Example preferences definition:

class UserPreferences : Preferences() {
 var emailAccount by stringPref()
 var allowAnonymousLogging by booleanPref()
}

Example usage:

preferences.allowAnonymousLogging = false

Example listener (not exactly the cleanest-looking but it works):

preferences.addListener(object : Preferences.SharedPrefsListener {
    override fun onSharedPrefChanged(property: KProperty<*>) {
        if (UserPreferences::allowAnonymousLogging.name == property.name) {
            initLogging()
        }
    }
})

Preferences.kt

import android.content.Context
import android.content.SharedPreferences
import kotlin.reflect.KProperty

/**
 * Represents a single [SharedPreferences] file.
 *
 * Usage:
 *
 * `Preferences.init(context)`
 *
 * ```kotlin
 * class UserPreferences : Preferences() {
 *   var emailAccount by stringPref()
 *   var showSystemAppsPreference by booleanPref()
 * }
 * ```
 */
abstract class Preferences {
    companion object {
        private var context: Context? = null

        /**
         * Initialize PrefDelegate with a Context reference.
         *
         * **This method needs to be called before any other usage of PrefDelegate!!**
         */
        fun init(context: Context) {
            this.context = context
        }
    }

    private val prefs: SharedPreferences by lazy {
        if (context != null)
            context!!.getSharedPreferences(javaClass.simpleName, Context.MODE_PRIVATE)
        else
            throw IllegalStateException("Context was not initialized. Call Preferences.init(context) before using it")
    }

    private val listeners = mutableListOf<SharedPrefsListener>()

    abstract class PrefDelegate<T>(val prefKey: String?) {


        abstract operator fun getValue(thisRef: Any?, property: KProperty<*>): T
        abstract operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T)
    }

    interface SharedPrefsListener {
        fun onSharedPrefChanged(property: KProperty<*>)
    }

    fun addListener(sharedPrefsListener: SharedPrefsListener) {
        listeners.add(sharedPrefsListener)
    }

    fun removeListener(sharedPrefsListener: SharedPrefsListener) {
        listeners.remove(sharedPrefsListener)
    }

    fun clearListeners() = listeners.clear()

    fun stringPref(prefKey: String? = null, defaultValue: String? = null) = StringPrefDelegate(prefKey, defaultValue)

    inner class StringPrefDelegate(prefKey: String? = null, val defaultValue: String?) : PrefDelegate<String?>(prefKey) {
        override fun getValue(thisRef: Any?, property: KProperty<*>): String? = prefs.getString(prefKey ?: property.name, defaultValue)
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: String?) {
            prefs.edit().putString(prefKey ?: property.name, value).apply()
            onPrefChanged(property)
        }
    }

    fun intPref(prefKey: String? = null, defaultValue: Int = 0) = IntPrefDelegate(prefKey, defaultValue)

    inner class IntPrefDelegate(prefKey: String? = null, val defaultValue: Int) : PrefDelegate<Int>(prefKey) {
        override fun getValue(thisRef: Any?, property: KProperty<*>) = prefs.getInt(prefKey ?: property.name, defaultValue)
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: Int) {
            prefs.edit().putInt(prefKey ?: property.name, value).apply()
            onPrefChanged(property)
        }
    }


    fun floatPref(prefKey: String? = null, defaultValue: Float = 0f) = FloatPrefDelegate(prefKey, defaultValue)

    inner class FloatPrefDelegate(prefKey: String? = null, val defaultValue: Float) : PrefDelegate<Float>(prefKey) {
        override fun getValue(thisRef: Any?, property: KProperty<*>) = prefs.getFloat(prefKey ?: property.name, defaultValue)
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: Float) {
            prefs.edit().putFloat(prefKey ?: property.name, value).apply()
            onPrefChanged(property)
        }
    }


    fun booleanPref(prefKey: String? = null, defaultValue: Boolean = false) = BooleanPrefDelegate(prefKey, defaultValue)

    inner class BooleanPrefDelegate(prefKey: String? = null, val defaultValue: Boolean) : PrefDelegate<Boolean>(prefKey) {
        override fun getValue(thisRef: Any?, property: KProperty<*>) = prefs.getBoolean(prefKey ?: property.name, defaultValue)
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: Boolean) {
            prefs.edit().putBoolean(prefKey ?: property.name, value).apply()
            onPrefChanged(property)
        }
    }


    fun longPref(prefKey: String? = null, defaultValue: Long = 0L) = LongPrefDelegate(prefKey, defaultValue)

    inner class LongPrefDelegate(prefKey: String? = null, val defaultValue: Long) : PrefDelegate<Long>(prefKey) {
        override fun getValue(thisRef: Any?, property: KProperty<*>) = prefs.getLong(prefKey ?: property.name, defaultValue)
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: Long) {
            prefs.edit().putLong(prefKey ?: property.name, value).apply()
            onPrefChanged(property)
        }
    }


    fun stringSetPref(prefKey: String? = null, defaultValue: Set<String> = HashSet<String>()) = StringSetPrefDelegate(prefKey, defaultValue)

    inner class StringSetPrefDelegate(prefKey: String? = null, val defaultValue: Set<String>) : PrefDelegate<Set<String>>(prefKey) {
        override fun getValue(thisRef: Any?, property: KProperty<*>): Set<String> = prefs.getStringSet(prefKey ?: property.name, defaultValue)
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: Set<String>) {
            prefs.edit().putStringSet(prefKey ?: property.name, value).apply()
            onPrefChanged(property)
        }
    }

    private fun onPrefChanged(property: KProperty<*>) {
        listeners.forEach { it.onSharedPrefChanged(property) }
    }
}