方式一：
import android.content.Context
import android.content.SharedPreferences
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty
class MyPreference1<T>(private val context: Context,
val name: String,
private val default: T)
: ReadWriteProperty<Any?, T> {
private val prefs: SharedPreferences by lazy {
context.getSharedPreferences("default", Context.MODE_PRIVATE)
}
override fun getValue(thisRef: Any?, property: KProperty<*>): T {
return getPreference(name, default)
}
override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
putPreference(name, value)
}
@Suppress("UNCHECKED_CAST")
private fun <T> getPreference(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 not be saved into Preferences")
}
res as T
}
private fun <U> putPreference(name: String, value: U) = 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 be saved into Preferences")
}.apply()
}
}
方式二：
import android.annotation.SuppressLint
import android.content.Context
import android.content.SharedPreferences
import kotlin.reflect.KProperty
class MyPreference2<T>(val name: String, private val default: T) {
private val prefs: SharedPreferences by lazy {
App.instance.applicationContext.getSharedPreferences(name, Context.MODE_PRIVATE)
}
operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
return getSharePreferences(name, default)
}
operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
putSharePreferences(name, value)
}
@Suppress("UNCHECKED_CAST")
private fun getSharePreferences(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 of data cannot be saved!")
}
return res as T
}
@SuppressLint("CommitPrefEdits")
private fun putSharePreferences(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 of data cannot be saved!")
}.apply()
}
}
class App : Application() {
companion object {
// 伴生对象
lateinit var instance: App
private set
}
override fun onCreate() {
super.onCreate()
instance = this
}
}
测试
class MainActivity : AppCompatActivity() {
var a by MyPreference1(this@MainActivity, "a", 1)
var b by MyPreference2("b", 100)
@SuppressLint("SetTextI18n")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
tv_result.text = "" + a
}
@SuppressLint("SetTextI18n")
@Suppress("UNUSED_EXPRESSION")
fun onclick(view: View) {
when (view.id) {
R.id.btn1 -> a++
R.id.btn2 -> tv_result.text = "" + a
R.id.btn3 -> b++
R.id.btn4 -> tv_result.text = "" + b
else -> "default"
}
}
}
