[Kotlin] 密封类总结

简介

sealed 修饰的类称为密封类，用来表示受限的类层次结构。

案例

代码语言：txt复制

// 外部无法实例化密封的类
// 外部只能实例化他的子类
sealed class Color {
    // 只能在内部继承密封类
    class Red(val value: Int) : Color()
    class Green(val value: Int) : Color()
    class Blue(val name: String) : Color()
}

fun isInstance(color: Color) {
    when (color) {
        // 必须写全所有条件，否则报错
        is Color.Red -> TODO()
        is Color.Green -> TODO()
        is Color.Blue -> TODO()
    }
}

案例

代码语言：txt复制

// 默认情况下，密封类的构造函数是私有的。
// 密封类的所有子类必须在同一文件中声明。
sealed class A {
    class B : A() {
        // this works.
        class E : A()
    }

    class C : A()
 
    init {
        println("sealed class A")
    } 
}
 
//this works 
class D : A() {
    // This won't work. Since sealed class is defined in another scope.
    class F: A() 
}

案例

代码语言：txt复制

// 在密封的类中添加数据类和对象 
sealed class A {
    class B : A()
    class C : A()

    object D : A() {
         fun name() {
             println("Object D")
         }
    }

    data class E(var name: String) : A()
}

演示

代码语言：txt复制

sealed class NetworkResult<out T> {
    data class Success<out T>(val value: T) : NetworkResult<T>()
    data class Failure(val throwable: Throwable?) : NetworkResult<Nothing>()
}

when (result) {
    is PokemonResult.Failure -> {
        // 进行失败提示
    }
    is PokemonResult.Success -> {
        // 进行成功处理
    }
}

代码语言：txt复制

sealed class PrchaseResult {
    sealed class GoogplayBilling: PrchaseResult(){
        data class Sucess(val purchseToken : String) : GoogplayBilling()
        data class Fail(val error : String) : GoogplayBilling()
        object Retry : GoogplayBilling()
        sealed class PurchaseAcknowledgement : GoogplayBilling(){
            object Sucess : PurchaseAcknowledgement()
            data class Fail(val errorCode : Int) : PurchaseAcknowledgement()
        }
    }
 
    sealed class Stripe: PrchaseResult(){
        data class Sucess(val purchseToken : String) : Stripe()
        data class Fail(val error : String) : Stripe()
        object Retry : Stripe()
        sealed class PurchaseAcknowledgement : Stripe(){
            object Sucess : PurchaseAcknowledgement()
            data class Fail(val errorCode : Int) : PurchaseAcknowledgement()
        }
    }
 
    sealed class PayYouMoney: PrchaseResult(){
        data class Sucess(val purchseToken : String) : PayYouMoney()
        data class Fail(val error : String) : PayYouMoney()
        object Retry : PayYouMoney()
        sealed class PurchaseAcknowledgement : PayYouMoney(){
            object Sucess : PurchaseAcknowledgement()
            data class Fail(val errorCode : Int) : PurchaseAcknowledgement()
        }
    }
}

when(signal){
    // GooglePlay Billing related
    is PrchaseResult.GoogplayBilling.Sucess -> { }
    is PrchaseResult.GoogplayBilling.Fail -> { }
    is PrchaseResult.GoogplayBilling.Retry -> { }
    is PrchaseResult.GoogplayBilling.PurchaseAcknowledgement.Sucess -
    is PrchaseResult.GoogplayBilling.PurchaseAcknowledgement.Fail -> 
    // PayYouMoney Billing related
    is PrchaseResult.PayYouMoney.Sucess -> { }
    is PrchaseResult.PayYouMoney.Fail -> { }
    is PrchaseResult.PayYouMoney.Retry -> { }
    is PrchaseResult.PayYouMoney.PurchaseAcknowledgement.Sucess -> { }
    is PrchaseResult.PayYouMoney.PurchaseAcknowledgement.Fail -> { }
    // PayYouMoney Billing related
    is PrchaseResult.Stripe.Sucess -> { }
    is PrchaseResult.Stripe.Fail -> { }
    is PrchaseResult.Stripe.Retry -> { }
    is PrchaseResult.Stripe.PurchaseAcknowledgement.Sucess -> { }
    is PrchaseResult.Stripe.PurchaseAcknowledgement.Fail -> { }
}

kotlin

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