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.extktimport android.content.Contextimport kotlin.properties.ReadWritePropertyimport kotlin.reflect.KProperty/** * Preference * * @author 祁连山™ * @date 2016-12-09 * @version 1.0 */class Preference
     
      (val context: Context, val name: String, val default: T) : ReadWriteProperty
      
        {    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 
        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  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.kotlinimport android.content.Intentimport android.os.Bundleimport android.support.v7.app.AppCompatActivityimport com.android.extkt.Preferenceimport rx.Observableimport rx.android.schedulers.AndroidSchedulersimport rx.schedulers.Schedulersimport java.util.concurrent.TimeUnitclass 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
     
       {        public operator fun getValue(thisRef: R, property: KProperty<*>): T    public operator fun setValue(thisRef: R, property: KProperty<*>, value: T)}
     

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      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.Contextimport kotlin.properties.ReadWritePropertyimport kotlin.reflect.KProperty/** * Preference * * @author 祁连山 * @date 2016-12-09 * @version 1.0 */class Preference
     
      (val context: Context) : ReadWriteProperty
      
        {    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 
        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  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：

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