kotlin委托属性

Posted 2021-01-28 loaderman

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!