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.byStudyimport kotlin.properties.ReadOnlyProperty
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KPropertyfun 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.byStudyimport kotlin.properties.ReadOnlyProperty
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KPropertyfun 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.byStudyfun main() {val test by lazy{println("初始化了test")"hello"}println(test)
}

4.监听委托

package com.jmj.jetpackcomposecompositionlocal.byStudyimport kotlin.properties.Delegatesfun 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)
}