kotlin : SharedPreferences 与委托

最新推荐文章于 2023-07-12 21:53:29 发布

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本文介绍了一种使用Kotlin对Android的SharedPreferences进行封装的方法，通过创建泛型属性来简化读写操作，并提供了两种不同的实现方式。

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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"
        }
    }

}