How to set a value preference in Kotlin? - kotlin

Question

The following code is from a sample project about Kotlin, I can use Code 1 to get a value of a shared preferences, but I can set a value of a shared preferences?
I can't find those code in the sample project, could you tell me how I can do? Thanks!
Code 1
class SettingsActivity : AppCompatActivity() {
companion object {
val ZIP_CODE = "zipCode"
val DEFAULT_ZIP = 94043L
}
var zipCode: Long by DelegatesExt.preference(this, ZIP_CODE, DEFAULT_ZIP)
}
Code 2
object DelegatesExt {
fun <T> notNullSingleValue() = NotNullSingleValueVar<T>()
fun <T> preference(context: Context, name: String, default: T) = Preference(context, name, default)
}
class NotNullSingleValueVar<T> {
private var value: T? = null
operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
return value ?: throw IllegalStateException("${property.name} not initialized")
}
operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
this.value = if (this.value == null) value
else throw IllegalStateException("${property.name} already initialized")
}
}
class Preference<T>(val context: Context, val name: String, val default: T) {
val prefs: SharedPreferences by lazy { context.getSharedPreferences("default", Context.MODE_PRIVATE) }
operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
return findPreference(name, default)
}
operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
putPreference(name, value)
}
#Suppress("UNCHECKED_CAST")
private fun findPreference(name: String, default: T): T = with(prefs) {
val res: Any = when (default) {
is Long -> getLong(name, default)
is String -> getString(name, default)
is Int -> getInt(name, default)
is Boolean -> getBoolean(name, default)
is Float -> getFloat(name, default)
else -> throw IllegalArgumentException("This type can be saved into Preferences")
}
res as T
}
private fun putPreference(name: String, value: T) = with(prefs.edit()) {
when (value) {
is Long -> putLong(name, value)
is String -> putString(name, value)
is Int -> putInt(name, value)
is Boolean -> putBoolean(name, value)
is Float -> putFloat(name, value)
else -> throw IllegalArgumentException("This type can't be saved into Preferences")
}.apply()
}
}
And More
If the function putPreference is public, I can set value of a shared preferences using the code below, but it's ugly
class SettingsActivity : AppCompatActivity() {
companion object {
val ZIP_CODE = "zipCode"
val DEFAULT_ZIP = 94043L
}
DelegatesExt.Preference(this, ZIP_CODE, DEFAULT_ZIP).putPreference( ZIP_CODE,"99999L");
}

Answer 1

That's what operator fun setValue is for: you just write
activity.zipCode = 1L
(where activity is a SettingsActivity) or
zipCode = 1L
(inside SettingsActivity or a class extending it) and it'll call setValue(activity, activity::zipCode, 1L) which calls putPreference("zipCode", 1L). See https://kotlinlang.org/docs/reference/delegated-properties.html for more.