【設計模式】之訪問者模式

• UML

• 舉例

//人
    abstract class Person
    {
        //獲得狀態對象
        public abstract void Accept(Action visitor);
    }

//狀態
abstract class Action
    {
        //得到男人的反應
        public abstract void GetManConclusion(Man concreteElementA);
        //得到女人的反應
        public abstract void GetWomanConclusion(Woman concreteElementB);
    }

 //男人
    class Man : Person
    {
        public override void Accept(Action visitor)
        {
            visitor.GetManConclusion(this);
        }
    }

//女人
    class Woman : Person
    {
        public override void Accept(Action visitor)
        {
            visitor.GetWomanConclusion(this);
        }
    }

//結婚狀態
    class Amativeness : Action
    {
        public override void GetManConclusion(Man concreteElementA)
        {
            Console.WriteLine("男人戀愛時，不懂也要裝懂");
        }

        public override void GetWomanConclusion(Woman concreteElementB)
        {
            Console.WriteLine("女人戀愛時，懂也要裝不懂");
        }
    }

//失敗
    class Failing : Action
    {
        public override void GetManConclusion(Man concreteElementA)
        {
            Console.WriteLine("男人失敗時，悶頭喝酒，誰也不用勸");
        }

        public override void GetWomanConclusion(Woman concreteElementB)
        {
            Console.WriteLine("女人失敗時，眼淚汪汪，誰也勸不動");
        }
    }

//成功
    class Success : Action
    {
        public override void GetManConclusion(Man concreteElementA)
        {
            Console.WriteLine("男人成功時，背後多半有一個偉大的女人");
        }

        public override void GetWomanConclusion(Woman concreteElementB)
        {
            Console.WriteLine("女人成功時，背後多半有一個不成功的男人");
        }
    }

//對象結構
    class ObjectStructure
    {
        private IList<Person> elements = new List<Person>();

        //增加
        public void Attach(Person element)
        {
            elements.Add(element);
        }
        
        //移除
        public void Detach(Person element)
        {
            elements.Remove(element);
        }
        
        //查看每個對象對於某一狀態的反應
        public void Display(Action visitor)
        {
            foreach(Person e in elements)
            {
                e.Accept(visitor);
            }
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            ObjectStructure structure = new ObjectStructure();
            structure.Attach(new Man());
            structure.Attach(new Woman());

            structure.Display(new Failing());
            structure.Display(new Amativeness());
            structure.Display(new Success());
        }
    }