SharedPreferences Property Delegate

Without property delegation

class UserSettings(
   private val prefs: SharedPreferences
) {
   
   var name: String 
   	 get() = prefs.getString("name", "") ?: ""
	 set(value) {
         prefs.edit {
            putString("name", value)
         }
     }
   
   var age: Int 
   	 get() = prefs.getInt("age", 0) ?:0
	 set(value) {
         prefs.edit {
            putInt("name", value)
         }
     } 
}

 

Using delegate looks much cleaner

class UserSettings(
    private val prefs: SharedPreferences
) {

    var name by prefs.string()

    var age by prefs.int()
    
}

 

Add generic delegate

class SharedPreferencesDelegate<T>(
    private val delegate: SharedPreferences,
    private val key: String? = null,
    private val defaultValue: T,
    private val getter: SharedPreferences.(String, T) -> T?,
    private val setter: SharedPreferences.Editor.(String, T) -> Unit
) : ReadWriteProperty<Any, T> {
    override fun getValue(thisRef: Any, property: KProperty<*>): T {
        return delegate.getter(key ?: property.name, defaultValue) ?: defaultValue
    }

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

 

Exensions for supported type

fun SharedPreferences.string(
    key: String? = null,
    defaultValue: String = ""
) = SharedPreferencesDelegate(
    delegate = this,
    key = key,
    defaultValue = defaultValue,
    getter = SharedPreferences::getString,
    setter = SharedPreferences.Editor::putString
)

fun SharedPreferences.int(
    key: String? = null,
    defaultValue: Int = 0
) = SharedPreferencesDelegate(
    delegate = this,
    key = key,
    defaultValue = defaultValue,
    getter = SharedPreferences::getInt,
    setter = SharedPreferences.Editor::putInt
)

fun SharedPreferences.long(
    key: String? = null,
    defaultValue: Long = 0L
) = SharedPreferencesDelegate(
    delegate = this,
    key = key,
    defaultValue = defaultValue,
    getter = SharedPreferences::getLong,
    setter = SharedPreferences.Editor::putLong
)

fun SharedPreferences.float(
    key: String? = null,
    defaultValue: Float = 0f
) = SharedPreferencesDelegate(
    delegate = this,
    key = key,
    defaultValue = defaultValue,
    getter = SharedPreferences::getFloat,
    setter = SharedPreferences.Editor::putFloat
)

fun SharedPreferences.boolean(
    key: String? = null,
    defaultValue: Boolean = false
) = SharedPreferencesDelegate(
    delegate = this,
    key = key,
    defaultValue = defaultValue,
    getter = SharedPreferences::getBoolean,
    setter = SharedPreferences.Editor::putBoolean
)

fun SharedPreferences.stringSet(
    key: String? = null,
    defaultValue: Set<String> = emptySet()
) = SharedPreferencesDelegate(
    delegate = this,
    key = key,
    defaultValue = defaultValue,
    getter = SharedPreferences::getStringSet,
    setter = SharedPreferences.Editor::putStringSet
)