Design patterns IV : Decorator/Wrapper Pattern

/*

Author: Jiangong SUN

*/

Decorators provide a flexible alternative to subclassing for extending functionality.

public class DecoratorPattern
    {
         /*
         * decorator和wrapper是一個設計模式
         * 用途：用來擴展已有類的功能
         * 實現步驟：
         * 先定義一個interface，然後建立一個類繼承這個接口，並實現接口裡的方法
         * 建立一個包裝類繼承同一個接口，並在這個包裝類的構造器中使用接口的實例做參數。
         * 建立實際包裝類繼承包裝類，重寫接口定義的方法，並可以創建自己特有的方法。
         */
        public interface IComponent
        {
            void Operation();
        }

        public class ConcreteComponent : IComponent
        {
            public void Operation()
            {
                Console.WriteLine("ConcreteComponent operation");
            }
        }

        public class Decorator : IComponent
        {
            private readonly IComponent _decoratedComponent;

            public Decorator(IComponent iComponent)
            {
                _decoratedComponent = iComponent;
            }

            public void Operation()
            {
                _decoratedComponent.Operation();
            }
        }

        public class ConcreteDecoratorA : Decorator
        {
            private string _addState;

            public ConcreteDecoratorA(Decorator decorator)
                : base(decorator)
            {
            }

            public new void Operation()
            {
                base.Operation();
                _addState = "New State";
                Console.WriteLine("ConcreteDecoratorA.Operation");
            }
            public void CustomOperation()
            {
                Console.WriteLine("ConcreteDecoratorA custom Operation");
            }
        }

        public static void Main()
        {
            ConcreteComponent concreteComponent = new ConcreteComponent();
            concreteComponent.Operation();

            Decorator decorator = new Decorator(concreteComponent);
            ConcreteDecoratorA concreteDecoratorA = new ConcreteDecoratorA(decorator);
            concreteDecoratorA.Operation();
            concreteDecoratorA.CustomOperation();

            Console.ReadKey();
        }
    }