C# 設計模式實戰：Decorator 裝飾模式完整解析（一）

模式意圖

動態地給物件增加額外職責。就增加功能而言，Decorator 比產生子類別更靈活。

應用場景：遊戲武器系統擴展

初版武器系統未考慮強化/磨損。策劃後續需求：強化系統、修理系統。武器需提供強化、磨損、修理方法。修改原類別違反開閉原則。繼承方案：武器類型 × 功能組合 → 類別爆炸（可強化不可磨損、可磨損不可強化、兩者皆可...）。引入 Decorator 靈活組合職責。

完整實作代碼

using System;
using System.Collections.Generic;
using System.Text;

namespace DecoratorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            Weapon w = new Rifle();
            w.ShowInfo();

            Enhance enhancedWeapon = new Enhance(w);
            enhancedWeapon.EnhanceAmmo();
            enhancedWeapon.ShowInfo();

            Wear wornWeapon = new Wear(w);
            wornWeapon.WearByRate(0.8);
            wornWeapon.ShowInfo();
        }
    }

    abstract class Weapon // Component
    {
        private double _ammo, _attack, _speed;
        private string _name;
        public double Ammo { get { return _ammo; } set { _ammo = value; } }
        public double Attack { get { return _attack; } set { _attack = value; } }
        public double Speed { get { return _speed; } set { _speed = value; } }
        public string Name { get { return _name; } set { _name = value; } }
        public abstract void ShowInfo();
    }

    class Rifle : Weapon // ConcreteComponent
    {
        public Rifle() { Ammo = 100; Attack = 10; Speed = 5; Name = "Rifle"; }
        public override void ShowInfo()
        {
            Console.WriteLine($"ammo\t{Ammo}");
            Console.WriteLine($"attack\t{Attack}");
            Console.WriteLine($"speed\t{Speed}");
            Console.WriteLine($"name\t{Name}");
        }
    }

    abstract class Decorator : Weapon // Decorator
    {
        protected Weapon _w;
        public Decorator(Weapon w) { _w = w; }
        public override void ShowInfo() => _w.ShowInfo();
    }

    class Enhance : Decorator // ConcreteDecorator
    {
        public Enhance(Weapon w) : base(w) { }
        public void EnhanceAmmo()
        {
            _w.Ammo += 20;
            Console.WriteLine(">>>>>>>>>> Enhanced");
        }
    }

    class Wear : Decorator
    {
        public Wear(Weapon w) : base(w) { }
        public void WearByRate(double rate)
        {
            _w.Speed *= rate;
            _w.Attack *= rate;
            Console.WriteLine(">>>>>>>>>> Worn");
        }
    }
}

核心結構特徵

• Decorator 繼承 Component → 型別相容
• Decorator 持有 Component 實例 → 委派核心行為
• ConcreteDecorator 新增方法（EnhanceAmmo, WearByRate）→ 擴展職責
• 可多層包裝：new Wear(new Enhance(new Rifle()))

兩種裝飾模式變體