kotlin委托属性

fun main(arg: Array<String>) {

    val myClass1 = myClass1()

    myClass1.name="mycalsss1"

    val myClass2 = myClass2()

    myClass2.name="myclass2"

    println(myClass1.name)

    println(myClass2.name)

}

class myClass1{

    var name:String =""

    get() :String{

        println("mycalsss1.get 被调用")

        return field

    }

    set(value:String) {

        println("myclass1.set 被调用")

        field=value

    }

}

class myClass2{

    var name:String =""

        get() :String{

            println("mycalsss2.get 被调用")

            return field

        }

        set(value:String) {

            println("myclass2.set 被调用")

            field=value

        }

}

输出:

myclass1.set 被调用

myclass2.set 被调用

mycalsss1.get 被调用

mycalsss1

mycalsss2.get 被调用

myclass2

上面代码冗余,所谓委托类,就是一个包含getValue和setValue函数的类,这两个函数operator声明

在使用委托类时,需要by关键字,创建委托类实例的代码放在by后面

如下

import kotlin.reflect.KProperty

fun main(arg: Array<String>) {

    val myClass1 = myClass1()

    myClass1.name = "mycalss1"

    val myClass2 = myClass2()

    myClass2.name = "myclass2"

    println(myClass1.name)

    println(myClass2.name)

}

class delegate {

    var name: String = ""

    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {

        val classname = thisRef.toString().substringBefore("@")

        println("$classname get被调用")

        return name

    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {

        val classname = thisRef.toString().substringBefore("@")

        println("$classname set被调用")

        name = value

    }

}

class myClass1 {

    var name: String by delegate()

}

class myClass2 {

    var name: String by delegate()

}

输出结果和上面一样!