[Kotlin] Decorator Pattern 예시코드 - 코틀린으로 쓴 디자인 패턴

예시

abstract class Component {
    abstract fun operate(): String
}

class ConcreteComponent : Component() {
    override fun operate(): String {
        return "This is ConcreteComponent"
    }
}

abstract class Decorator(val component: Component) : Component() {
    abstract override fun operate(): String
}

class ConcreteDecorator(component: Component) : Decorator(component) {

    override fun operate(): String {
        return component.operate() + "with ConcreteDecorator"
    }
}

• Client

fun main() {
    var concreteComponent: Component = ConcreteComponent()

    concreteComponent = ConcreteDecorator(concreteComponent)
    concreteComponent = ConcreteDecorator(concreteComponent)
    concreteComponent.operate()
}

개념

데코레이터 패턴은 이 객체를 사용하는 코드를 변경하지 않으면서 객체에 추가행동을 더해줄 수 있는 방법이다. 상속보다 유연하게 사용할 수 있다.

• Component → 기본이 되는 개념 (음료)

• ConcreteComponent → 개념을 구현한 구현체 (에스프레소)

• Decorator → 장식의 틀

• DecoratorComponent → 구현체의 장식 (우유, 휘핑크림)

비유

• 카페

  

  • Component → 음료

  • ConcreteComponent → 에스프레소, 하우스 블렌드, 다크 로스트

  • DecoratorComponent → 모카, 우유, 두유, 휘핑

  abstract class Beverage {
      var description = "제목 없음"
      abstract fun cost(): Double
  }
  
  class Espresso : Beverage() {
      init {
          description = "에스프레소"
      }
      
      override fun cost(): Double {
          return 1.99
      }
  }
  
  class HouseBlend : Beverage() {
      init {
          description = "하우스 블렌드"
      }
  
      override fun cost(): Double {
          return 0.89
      }
  }
  
  abstract class CondimentDecorator(val beverage: Beverage) : Beverage() {
      abstract fun getDescription(): String
  }
  
  class Mocha(beverage: Beverage) : CondimentDecorator(beverage) {
      override fun getDescription(): String {
          return "${beverage.description}, 모카"
      }
  
      override fun cost(): Double {
          return beverage.cost() + 0.20
      }
  }
  
  class Whip(beverage: Beverage) : CondimentDecorator(beverage) {
      override fun getDescription(): String {
          return "${beverage.description}, 휘핑"
      }
  
      override fun cost(): Double {
          return beverage.cost() + 0.15
      }
  }

• 안드로이드 Notification

  • Comonent → 알림

  • ConcreteComponent → 아이콘, 제목, 내용, PendingIntent 등이 지정되어있는 기본 Notification

  • DecoratorComponent → LagreIcon, BigPictureStyle 등등

  abstract class NotificationComponent {
      lateinit var notificationBuilder: NotificationCompat.Builder
      fun build() : Notification {
          return notificationBuilder.build()
      }
  
      abstract fun createNotificationBuilder(
          context: Context,
          pendingIntent: PendingIntent,
          title: String,
          body: String,
          channelId: String
      ): NotificationCompat.Builder
  }
  
  class BaseNotification: NotificationComponent() {
      override fun createNotificationBuilder(
          context: Context,
          pendingIntent: PendingIntent,
          title: String,
          body: String,
          channelId: String
      ): NotificationCompat.Builder {
  
          notificationBuilder =  NotificationCompat.Builder(context, channelId)
              .setSmallIcon(R.drawable.ic_launcher_transparent)
              .setColor(ContextCompat.getColor(context, R.color.icon_color))
              .setContentTitle(title)
              .setContentText(body)
              .setContentIntent(pendingIntent)
              .setAutoCancel(true)
              .setPriority(NotificationCompat.PRIORITY_HIGH)
              .setDefaults(NotificationCompat.DEFAULT_ALL)
          return notificationBuilder
      }
  }
  
  abstract class NotificationDecorator(val component: NotificationComponent): NotificationComponent()
  
  class LargeIconDecorator(component: NotificationComponent, private val largeIcon:Bitmap) : NotificationDecorator(component) {
      override fun createNotificationBuilder(
          context: Context,
          pendingIntent: PendingIntent,
          title: String,
          body: String,
          channelId: String
      ): NotificationCompat.Builder {
          notificationBuilder = component.createNotificationBuilder(context, pendingIntent, title, body, channelId)
              .setLargeIcon(largeIcon)
          return notificationBuilder
      }
  }
  
  class BigPictureDecorator(component: NotificationComponent, private val image: Bitmap) : NotificationDecorator(component) {
      override fun createNotificationBuilder(
          context: Context,
          pendingIntent: PendingIntent,
          title: String,
          body: String,
          channelId: String
      ): NotificationCompat.Builder {
          val bigPictureStyle = NotificationCompat.BigPictureStyle().also {
              it.setBigContentTitle(title)
              it.setSummaryText(body)
              it.bigPicture(image)
          }
  
          notificationBuilder = component.createNotificationBuilder(context, pendingIntent, title, body, channelId)
              .setStyle(bigPictureStyle)
  
          return notificationBuilder
      }
  }

  • 실제로 동작하는 코드입니다.

  • Caller 부분
    • Java

    NotificationComponent notification = new BaseNotification();
    notification = new LargeIconDecorator(notification, image);
    notification = new BigPictureDecorator(notification, image);
    notification.createNotificationBuilder(this, pendingIntent, title, body, CHANNEL_ID);
    
    notificationManager.notify(CHAT_NOTIFICATION_ID, notification.build());

    • Kotlin

    var notification: NotificationComponent = BaseNotification()
    notification = LargeIconDecorator(notification, image)
    notification = BigPictureDecorator(notification, image)
    notification.createNotificationBuilder(this, pendingIntent, title, body, CHANNEL_ID)
    
    notificationManager.notify(CHAT_NOTIFICATION_ID, notification.build())

장단점

장점

• 서브클래스를 새로 만들지 않아도 객체의 행동을 추가할 수 있다.

• 런타임에 행동을 추가할 수 있다.

• SRP
  • 각 ConcreteDecorator가 하나의 책임을 가진다.

단점

• 특정 데코레이터를 제거하기 어렵다.

• 데코레이터의 순서에 의존한다.

이런 경우가 생길 수 있다.

출처

https://refactoring.guru/ko/design-patterns/decorator

Uploaded by N2T