Berikut ini adalah cara menggunakan Properti Delegasi Kotlin yang saya ambil dari sini , tetapi diperluas dan memungkinkan mekanisme sederhana untuk mendapatkan / mengatur properti SharedPreference.
Untuk String, Int, Long, Floatatau Boolean, menggunakan standar SharePreference getter (s) dan setter (s). Namun, untuk semua kelas data lainnya, ia menggunakan GSON untuk membuat serial ke a String, untuk setter. Kemudian deserializes ke objek data, untuk pengambil.
Mirip dengan solusi lain, ini membutuhkan penambahan GSON sebagai ketergantungan pada file gradle Anda:
implementation 'com.google.code.gson:gson:2.8.6'
Berikut adalah contoh kelas data sederhana yang ingin kami simpan dan simpan ke SharedPreferences:
data class User(val first: String, val last: String)
Ini adalah satu kelas yang mengimplementasikan delegasi properti:
object UserPreferenceProperty : PreferenceProperty<User>(
key = "USER_OBJECT",
defaultValue = User(first = "Jane", last = "Doe"),
clazz = User::class.java)
object NullableUserPreferenceProperty : NullablePreferenceProperty<User?, User>(
key = "NULLABLE_USER_OBJECT",
defaultValue = null,
clazz = User::class.java)
object FirstTimeUser : PreferenceProperty<Boolean>(
key = "FIRST_TIME_USER",
defaultValue = false,
clazz = Boolean::class.java
)
sealed class PreferenceProperty<T : Any>(key: String,
defaultValue: T,
clazz: Class<T>) : NullablePreferenceProperty<T, T>(key, defaultValue, clazz)
@Suppress("UNCHECKED_CAST")
sealed class NullablePreferenceProperty<T : Any?, U : Any>(private val key: String,
private val defaultValue: T,
private val clazz: Class<U>) : ReadWriteProperty<Any, T> {
override fun getValue(thisRef: Any, property: KProperty<*>): T = HandstandApplication.appContext().getPreferences()
.run {
when {
clazz.isAssignableFrom(String::class.java) -> getString(key, defaultValue as String?) as T
clazz.isAssignableFrom(Int::class.java) -> getInt(key, defaultValue as Int) as T
clazz.isAssignableFrom(Long::class.java) -> getLong(key, defaultValue as Long) as T
clazz.isAssignableFrom(Float::class.java) -> getFloat(key, defaultValue as Float) as T
clazz.isAssignableFrom(Boolean::class.java) -> getBoolean(key, defaultValue as Boolean) as T
else -> getObject(key, defaultValue, clazz)
}
}
override fun setValue(thisRef: Any, property: KProperty<*>, value: T) = HandstandApplication.appContext().getPreferences()
.edit()
.apply {
when {
clazz.isAssignableFrom(String::class.java) -> putString(key, value as String?) as T
clazz.isAssignableFrom(Int::class.java) -> putInt(key, value as Int) as T
clazz.isAssignableFrom(Long::class.java) -> putLong(key, value as Long) as T
clazz.isAssignableFrom(Float::class.java) -> putFloat(key, value as Float) as T
clazz.isAssignableFrom(Boolean::class.java) -> putBoolean(key, value as Boolean) as T
else -> putObject(key, value)
}
}
.apply()
private fun Context.getPreferences(): SharedPreferences = getSharedPreferences(APP_PREF_NAME, Context.MODE_PRIVATE)
private fun <T, U> SharedPreferences.getObject(key: String, defValue: T, clazz: Class<U>): T =
Gson().fromJson(getString(key, null), clazz) as T ?: defValue
private fun <T> SharedPreferences.Editor.putObject(key: String, value: T) = putString(key, Gson().toJson(value))
companion object {
private const val APP_PREF_NAME = "APP_PREF"
}
}
Catatan: Anda tidak perlu memperbarui apa pun di sealed class. Properti yang didelegasikan adalah Obyek / Lajang UserPreferenceProperty, NullableUserPreferencePropertydan FirstTimeUser.
Untuk menyiapkan objek data baru untuk disimpan / didapatkan dari SharedPreferences, sekarang semudah menambahkan empat baris:
object NewPreferenceProperty : PreferenceProperty<String>(
key = "NEW_PROPERTY",
defaultValue = "",
clazz = String::class.java)
Akhirnya, Anda dapat membaca / menulis nilai ke SharedPreferences dengan hanya menggunakan bykata kunci:
private var user: User by UserPreferenceProperty
private var nullableUser: User? by NullableUserPreferenceProperty
private var isFirstTimeUser: Boolean by
Log.d("TAG", user) // outputs the `defaultValue` for User the first time
user = User(first = "John", last = "Doe") // saves this User to the Shared Preferences
Log.d("TAG", user) // outputs the newly retrieved User (John Doe) from Shared Preferences