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次のコードAは私がコードA.クラスが必要な理由Preference <T>はオブジェクトでラップする必要がありますか？
を使用する場合、私はオブジェクトDelegatesExt
で、なぜ著者ラップクラスのプリファレンス（...）を理解していない呼び出すためにprivate var zipCode: Long by DelegatesExt.preference(this, ZIP_CODE, DEFAULT_ZIP)を使用することができます
https://github.com/antoniolg/Kotlin-for-Android-Developers/blob/master/app/src/main/java/com/antonioleiva/weatherapp/extensions/DelegatesExtensions.kt
からです
コードBはもっとシンプルだと思いますが、コードBを使用すると呼び出すにはを使用できます
なぜクラスが必要なのかオブジェクトでラップするのはなぜですか？ロングDelegatesExt.preference（これ、ZIP_CODE、DEFAULT_ZIP）によってときに呼び出す：私は民間のVaRの郵便番号を使用することができます
コードA
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 =
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>(private val context: Context, private val name: String,
private val default: T) {
private val prefs: SharedPreferences by lazy {
context.getSharedPreferences("default", Context.MODE_PRIVATE)
}
operator fun getValue(thisRef: Any?, property: KProperty<*>): T = 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
}
@SuppressLint("CommitPrefEdits")
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()
}
}
コードB
class NotNullSingleValueVar<T> {
private var value: T? = null
operator fun getValue(thisRef: Any?, property: KProperty<*>): T =
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>(private val context: Context, private val name: String,
private val default: T) {
private val prefs: SharedPreferences by lazy {
context.getSharedPreferences("default", Context.MODE_PRIVATE)
}
operator fun getValue(thisRef: Any?, property: KProperty<*>): T = 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
}
@SuppressLint("CommitPrefEdits")
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()
}
}