c#设计模式之策略者模式(Strategy Pattern)

场景出发

假设存在如下游戏场景:

1:角色可以装备木剑,铁剑,魔剑3种装备,分别对怪物造成20HP,50HP,100HP伤害(未佩戴装备则无法攻击);

2角色可以向怪物攻击,一次攻击后损失角色所佩戴装备的HP伤害,当HP损失完毕后,怪物死亡;

不假思索地我会写出如下的代码:

 1   class Monster
 2     {
 3         public string Name { get; set; }
 4         public int HP { get; set; }
 5         /// <summary>
 6         /// 怪物被攻击后提示
 7         /// </summary>
 8         /// <param name="loss">武器造成的HP伤害损失</param>
 9         public void Warn(int loss)
10         {
11             if (HP <= 0)
12             {
13                 Console.WriteLine($"怪物{Name}已经死亡");
14                 return;
15             }
16 
17             HP -= loss;
18 
19             Console.WriteLine($"怪物{Name}受到{loss}HP伤害");
20 
21             if (HP <= 0)
22             {
23                 Console.WriteLine($"怪物{Name}被打死了");
24             }
25         }
26     }

View Code

 1   class Role
 2     {
 3         public string Name { get; set; }
 4         public string Weapon { get; set; }
 5         /// <summary>
 6         /// 武器攻击
 7         /// </summary>
 8         /// <param name="monster">攻击的怪物对象</param>
 9         public void Attack(Monster monster)
10         {
11             if (Weapon == "WoodenSword")
12             {
13                 Console.WriteLine($"{Name}用木剑攻击了{monster.Name}");
14                 monster.Warn(25);
15             }
16 
17             else if (Weapon == "IronSword")
18             {
19                 Console.WriteLine($"{Name}用铁剑攻击了{monster.Name}");
20                 monster.Warn(50);
21             }
22             else if (Weapon == "MagicSword")
23             {
24                 Console.WriteLine($"{Name}用魔剑攻击了{monster.Name}");
25                 monster.Warn(100);
26             }
27             else
28             {
29                 Console.WriteLine($"{Name}没有武器,无法攻击");
30             }
31         }
32     }

View Code

 1     class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             var monster = new Monster()
 6             {
 7                 Name = "沼泽首领",
 8                 HP = 80
 9             };
10             var role = new Role()
11             {
12                 Name = "狂战士",
13                 Weapon="IronSword"
14             };
15             role.Attack(monster);
16             role.Weapon = "WoodenSword";
17             role.Attack(monster);
18             role.Weapon = "MagicSword";
19             role.Attack(monster);
20 
21             Console.ReadKey();
22         }
23     }

View Code

相信不止我一个人会这样写,因为它能快速的"完美的"实现上述功能

回过头来再仔细观察这段代码,就感觉像在看一段"直肠子",所有的逻辑算法都集中到了一个管道上,只要有需求或逻辑上的的变化,那么就得直接去修改业务类

策略者模式

其实很多时候我们都会遇到上述这种情况,一个业务类中存在这种逻辑,多个if...else来判断选择逻辑策略,这个时候如果直接写入业务类,严重违背了OCP原则(开放关闭原则:对扩展开放,对修改关闭)

将上述的场景通过策略者模式来解决,代码如下

1    /// <summary>
2     /// 武器攻击的抽象
3     /// </summary>
4     public interface IWeaponStrategy
5     {
6         void WeaponAttack(Monster monster);
7     }

View Code

 1     public class WoodenSwordStrategy : IWeaponStrategy
 2     {
 3         public void WeaponAttack(Monster monster)
 4         {
 5             Console.WriteLine("木剑攻击");
 6             monster.Warn(20);
 7         }
 8     }
 9     public class IronSwordStrategy : IWeaponStrategy
10     {
11         public void WeaponAttack(Monster monster)
12         {
13             Console.WriteLine("铁剑攻击");
14             monster.Warn(50);
15         }
16     }
17 
18     public class MagicSwordStrategy : IWeaponStrategy
19     {
20         public void WeaponAttack(Monster monster)
21         {
22             Console.WriteLine("魔剑攻击");
23             monster.Warn(100);
24         }
25     }

View Code

 1    public class Monster
 2     {
 3         public string Name { get; set; }
 4         public int HP { get; set; }
 5 
 6         /// <summary>
 7         /// 怪物被攻击后提示
 8         /// </summary>
 9         /// <param name="loss">武器造成的HP伤害损失</param>
10         public void Warn(int loss)
11         {
12             if (HP <= 0)
13             {
14                 Console.WriteLine($"怪物{Name}已经死亡");
15                 return;
16             }
17 
18             HP -= loss;
19 
20             Console.WriteLine($"怪物{Name}受到{loss}HP伤害");
21 
22             if (HP <= 0)
23             {
24                 Console.WriteLine($"怪物{Name}被打死了");
25             }
26         }
27     }

View Code

1     class Role
2     {
3         public string Name { get; set; }
4         public IWeaponStrategy Weapon { get; set; }
5         public void Attack(Monster monster)
6         {
7             Weapon.WeaponAttack(monster);
8         }
9     }

View Code

 1     class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             var monster = new Monster()
 6             {
 7                 Name = "沼泽首领",
 8                 HP = 80
 9             };
10             var role = new Role()
11             {
12                 Name = "狂战士",
13                 Weapon=new IronSwordStrategy()
14             };
15             role.Attack(monster);
16             role.Weapon = new WoodenSwordStrategy();
17             role.Attack(monster);
18             role.Weapon = new MagicSwordStrategy();
19             role.Attack(monster);
20 
21             Console.ReadLine();
22         }
23     }