Kotlin 进阶学习委托

1.接口委托

package com.jmj.jetpackcomposecompositionlocal.byStudy

/**
 * 接口委托
 */
interface HomeDao{
    fun getAllData():List<String>
}

interface ADao{
        fun getById(id:Int):String
}

class HomeDaoImpl:HomeDao{
    override fun getAllData(): List<String> {
        return listOf("home")
    }

}
class ADaoImpl:ADao{
    override fun getById(id: Int): String {
        return "object id = $id"
    }

}
//这里多态也可以
class HomeService(homeDaoImpl: HomeDaoImpl,aDao: ADao):HomeDao by homeDaoImpl,ADao by aDao{
    fun getRedisData():String{
        return "redis"
    }
}

fun main() {
    val homeService = HomeService(HomeDaoImpl(),ADaoImpl())
    val allData = homeService.getAllData()
    println(allData)

    println(homeService.getById(3))
}

2.属性委托

package com.jmj.jetpackcomposecompositionlocal.byStudy

import kotlin.properties.ReadOnlyProperty
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

fun main() {
    var test:String  by MyTestClass()
    test="123"
    println(test)
}




//如果是只读变量 委托 就实现 ReadOnlyProperty 接口
//<第一个类型是我们属性所属的那个类，第二个类型是我们属性本身的类型>
class MyTestClass:ReadWriteProperty<Nothing?,String>{

    private  var myVar = ""

    override fun getValue(thisRef: Nothing?, property: KProperty<*>): String {
        println("调用了get方法")
        return myVar
    }

    override fun setValue(thisRef: Nothing?, property: KProperty<*>, value: String) {
        println("调用了set方法")
       myVar = value
    }


}

package com.jmj.jetpackcomposecompositionlocal.byStudy

import kotlin.properties.ReadOnlyProperty
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

fun main() {
   A().apply {
      this.aTest = "hello"
       println(aTest)
   }
}

class A{
    var aTest:String by MyTestClass()
}

class B{
    var aTest:String by MyTestClass()
}
//如果是只读变量 委托 就实现 ReadOnlyProperty 接口
//<第一个类型是我们属性所属的那个类，第二个类型是我们属性本身的类型>
class MyTestClass:ReadWriteProperty<Any,String>{

    private  var myVar = ""


    override fun getValue(thisRef: Any, property: KProperty<*>): String {
        return myVar
    }

    override fun setValue(thisRef: Any, property: KProperty<*>, value: String) {
        myVar =value
    }


}

3.延迟委托

package com.jmj.jetpackcomposecompositionlocal.byStudy

fun main() {
    val test by lazy{
        println("初始化了test")
        "hello"
    }
    
    println(test)
}

4.监听委托

package com.jmj.jetpackcomposecompositionlocal.byStudy

import kotlin.properties.Delegates

fun main() {
    var test by Delegates.observable("hello"){_, oldValue, newValue ->
        println("oldValue $oldValue")
        println("newValue $newValue")

    }

    test = "TEAt"
    test = "TEAt"
    test = "TEAt"
    println(test)
    println(test)
    println(test)
    println(test)
    println(test)
}