意图
动态地给一个对象添加一些额外的职责。就增加功能来说,Decorator模式相比生成子类更为灵活。
场景
在设计网络游戏的武器系统时,开始并没有考虑到武器的强化和磨损。之后,策划人员说希望给游戏增加强化系统和修理系统,那么我们的武器类型就需要对外提供强化、磨损、修理等方法了。发生这种改动是我们最不愿意看到的,按照设计原则,我们希望功能的扩展尽可能不要修改原来的程序。你可能会想到使用继承来实现,但是策划人员的需求是有的武器能磨损能修理,不能强化,有的武器能强化,但是不会磨损,有的武器既能强化还能磨损和修理。遇到这样的情况,继承的方案可能不适合了,一来继承的层次可能会很多,二来子类的数量可能会很多。
由此,引入装饰模式来解决这个问题。装饰模式使得我们能灵活赋予类额外的职责,并且使得设计和继承相比更合理。
示例代码
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
{
private double ammo;
public double Ammo
{
get { return ammo; }
set { ammo = value; }
}
private double attack;
public double Attack
{
get { return attack; }
set { attack = value; }
}
private double speed;
public double Speed
{
get { return speed; }
set { speed = value; }
}
private string name;
public string Name
{
get { return name; }
set { name = value; }
}
public abstract void ShowInfo();
}
class Rifle : Weapon
{
public Rifle()
{
this.Ammo = 100;
this.Attack = 10;
this.Speed = 5;
this.Name = "Rifle";
}
public override void ShowInfo()
{
Console.WriteLine(string.Format("ammo\t{0}", Ammo));
Console.WriteLine(string.Format("attack\t{0}", Attack));
Console.WriteLine(string.Format("speed\t{0}", Speed));
Console.WriteLine(string.Format("name\t{0}", Name));
}
}
abstract class Decorator : Weapon
{
protected Weapon w;
public Decorator(Weapon w)
{
this.w = w;
}
public override void ShowInfo()
{
w.ShowInfo();
}
}
class Enhance : Decorator
{
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 = w.Speed * rate;
w.Attack = w.Attack * rate;
Console.WriteLine(">>>>>>>>>>>>Worn");
}
}
}