Kotlin偏好设置

Kotlin的强悍震撼了我，android中每个应用都会用到SharedPreference在Kotlin中使用竟是如此简单！

package com.android.extkt

import android.content.Context
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

/**
 * Preference
 *
 * @author 祁连山™
 * @date 2016-12-09
 * @version 1.0
 */

class Preference<T>(val context: Context, val name: String, val default: T) : ReadWriteProperty<Any?, T> {

    val prefs by lazy { context.getSharedPreferences("default", Context.MODE_PRIVATE) }

    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return findPreference(name, default)
    }

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        putPreference(name, value)
    }

    private fun <U> findPreference(name: String, default: U): U = 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")
        }
        res as U
    }

    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 not be saved")
        }.apply()
    }
}

 使用时直接读取赋值，再也不用edit、commit，以我们最常用的引导页判断来说，如果是第一次进入应用跳转到GuideActivity，否则启动MainActivity，使用Kotlin码出来就是下面这个样子：

package com.android.kotlin

import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import com.android.extkt.Preference
import rx.Observable
import rx.android.schedulers.AndroidSchedulers
import rx.schedulers.Schedulers
import java.util.concurrent.TimeUnit

class SplashActivity : AppCompatActivity() {

    private var first: Boolean by Preference(this, "first", true)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_splash)

        val observable = Observable.timer(3000, TimeUnit.MILLISECONDS)
        observable.observeOn(AndroidSchedulers.mainThread())
        observable.subscribeOn(Schedulers.io())
        observable.subscribe({ route() })
    }

    override fun onBackPressed() {
        return
    }

    fun route(): Unit {
        var intent = Intent()
        if (first) {
            intent.setClass(this, GuideActivity::class.java)
            startActivity(intent)
            // 可以在这里直接存储first的值
            // first = false
            this.finish()
            return
        }
        intent.setClass(this, MainActivity::class.java)
        startActivity(intent)
        this.finish()
    }
}

在Kotlin中，声明成员属性，除了直接赋值，还可以用 Delegate 的方式来声明，这个 Delegate 需要根据成员的类型（val 或者 var）来提供相应的 getValue 和 setValue 方法，比如一个可读写的 Delegate，需要提供下面的方法：

public interface ReadWriteProperty<in R, T> {
    
    public operator fun getValue(thisRef: R, property: KProperty<*>): T

    public operator fun setValue(thisRef: R, property: KProperty<*>, value: T)
}

-------------------------------------------------------------我是分隔线-------------------------------------------------------------

      最近项目已经使用kt来完成，用到这里时，需要清除全部缓存数据，不好一个个赋值清除，Preference有clear()却没法用，这时就需要对Preference这个代理类进行改造，也没什么可多说的，只是因为上午改的时候写错了，发现没法使用，下午单独写个demo时才发现，分享出来。

package com.android.app

import android.content.Context
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

/**
 * Preference
 *
 * @author 祁连山
 * @date 2016-12-09
 * @version 1.0
 */

class Preference<T>(val context: Context) : ReadWriteProperty<Any?, T> {

    var key: String? = null
    var value: T? = null

    constructor(context: Context, name: String, default: T) : this(context) {
        key = name
        value = default
    }

    val prefs by lazy { context.getSharedPreferences("default", Context.MODE_PRIVATE) }

    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return findPreference(key!!, value!!)
    }

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        putPreference(key!!, value)
    }

    fun delete(vararg key: String): Unit {
        if (key.size == 0) {
            prefs.edit().clear().commit()
            return
        }
        for (i in 0..key.size) {
            prefs.edit().remove(key[i]).commit()
        }
    }

    private fun <U> findPreference(name: String, default: U): U = 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("The data can not be saved")
        }
        res as U
    }

    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("The data can not be saved")
        }.apply()
    }
}

      使用方法与原来无异，只是用到Preference对象时，用主构造方法来获取，代码如下：

...
var prefs = Preference(this)
prefs.delete()
...

代码出处：http://www.jcodecraeer.com
代码下载：https://pan.baidu.com/s/1eR4i4ca
其他资料：http://blog.csdn.net/TIANLANG3/article/details/53926273