实例：

• 模板类
• 委托属性/委托代理
• lazy修饰符
• with函数

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

    /***
     * 通过属性代理初始化共享参数对象
     * lazy:第一次使用时执行初始化
     */
    val prefs: SharedPreferences by lazy { context.getSharedPreferences("default", Context.MODE_PRIVATE) }

    /***
     * 接管属性值的获取行为
     * *:表示一个不确定的类型
     */
    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return findPreference(name, default)
    }


    /***
     * 接管属性值的修改行为
     */
    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        putPreference(name, value)
    }

    //利用with函数定义临时的命名空间
    private fun <T> 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")
        }
        return res as T
    }

    private fun <T> putPreference(name: String, value: T) = with(prefs.edit()) {
        //putInt、putString等方法返回Editor对象
        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() //commit方法和apply方法都表示提交修改
    }

}

调用

class PerferenceActivity : AppCompatActivity() {

    /***
     * by委托属性/委托代理
     */
    private var name: String by Perference(this, "name", "")
    private var age: String by Perference(this, "age", "")


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

        btn_save.setOnClickListener { v ->
            when {
                et_name.text.isEmpty() -> toast("请先填写name")
                et_age.text.isEmpty() -> toast("请先填写age")
                else -> {
                    name = et_name.text.toString()
                    age = et_age.text.toString()
                }
            }
        }

        btn_read.setOnClickListener { v ->
            tv_show.text = name + "\n" + age
        }
    }
}