枚舉類型位標緻[Flags]特性的使用以及為枚舉類型添加方法

假設有段代碼是這樣的，需要判斷角色裝備哪些武器，然後根據角色的這個屬性來進行其它的一些操作。這時候我們可以用枚舉來標記角色可以裝備的武器。

   public enum Equipment
    {
        刀,
        槍,
        箭,
        弓
    }

    public sealed class Player
    {
        internal Equipment equipmentState;//用於描述角色可以使用哪些武器
       //......其它成員
    }

這就有個問題了，當角色可以裝備多種武器的時候，難道要用多個變數去表示他可以使用的武器嗎？又或者是在Equipment類型中加入新的成員，刀和箭，刀和箭和弓...... 造成這種原因的是Player中的equipmentState只能表示一種狀態，不能表示多種狀態。

即它的值只能是刀,槍,箭,弓中的一個。

這時候可以用Flags特性為修飾Equipment類型。它可以讓equipmentState有能力可以表示成多種狀態，現在equipmentState就相當於集合一樣。

 1 namespace UsageOfFlagsAttribute
 2 {
 3     [Flags]
 4     public enum Equipment
 5     {
 6         NONE = 0x0000,
 7         刀 = 0x0001,
 8         槍 = 0x0002,
 9         箭 = 0x0004,
10         弓 = 0x0008
11     }
12 
13     public sealed class Player
14     {
15         internal Equipment equipmentState;//用於描述角色可以使用哪些武器
16     }
17 
18 
19     class Program
20     {
21         static void Main(string[] args)
22         {
23             Player player = new Player();
24             player.equipmentState = Equipment.刀 | Equipment.弓;  //可以表示成多種狀態的集合
25         }
26     }
27 }

用Flags標記後也就可以按位計算了，一般枚舉有3種按位計算。

按位或（“|”）：將指定的符號加入到枚舉實例中

按位與（”&“）：判斷枚舉實例中是否有指定的符號  

異或（”^“）：刪除枚舉實例中指定的符號

  class Program
    {
        static void Main(string[] args)
        {
            Player player = new Player();

            //按位或
            player.equipmentState = Equipment.刀;
            player.equipmentState = player.equipmentState | Equipment.弓;
            Console.WriteLine(player.equipmentState.ToString());//列印結果：刀,弓

            //按位與
            player.equipmentState = Equipment.刀 | Equipment.弓;
            player.equipmentState = player.equipmentState & Equipment.刀;
            Console.WriteLine(player.equipmentState.ToString());  //列印結果 ： 刀

            //異或
            player.equipmentState = Equipment.刀 | Equipment.弓;
            player.equipmentState = player.equipmentState ^ Equipment.弓;
            Console.WriteLine(player.equipmentState.ToString());  //列印結果 ： 刀

            Console.ReadKey();
        }
    }

但是每次都要寫  player.equipmentState = player.equipmentState ^ Equipment.弓;  這麼賦值代碼的可讀性不好，而且容易浪費時間。因此可以擴展方法來封裝這些操作。

 1  public static class EnumExtendMethods
 2     {
 3         /// <summary>
 4         /// 判斷位標緻的枚舉實例中是否有指定符號
 5         /// </summary>
 6         /// <param name="eqipment">實例</param>
 7         /// <param name="checkState">指定的符號</param>
 8         /// <returns></returns>
 9         public static bool Contains(this Equipment equipment,Equipment checkState)
10         {
11             if (checkState == 0)
12             {
13                 throw new ArgumentOutOfRangeException("checkState", "不能為NONE");
14             }
15             return (equipment & checkState) == checkState;
16         }
17 
18         /// <summary>
19         /// 將指定的符號從枚舉實例中移除
20         /// </summary>
21         /// <param name="equipment"></param>
22         /// <param name="removeState">指定要移除的符號</param>
23         /// <returns></returns>
24         public static Equipment Remove(this Equipment equipment, Equipment removeState)
25         {
26             return equipment ^ removeState;
27         }
28 
29         /// <summary>
30         /// 向枚舉實例中加入指定的符號
31         /// </summary>
32         /// <param name="equipment"></param>
33         /// <param name="addState"></param>
34         /// <returns></returns>
35         public static Equipment Append(this Equipment equipment, Equipment addState)
36         {
37             return equipment | addState;
38         }
39     }

現在可以這樣調用了

 1     class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             Player player = new Player();
 6 
 7             //按位或
 8             player.equipmentState = Equipment.刀;
 9             player.equipmentState = player.equipmentState.Append(Equipment.弓);
10             Console.WriteLine(player.equipmentState.ToString());//列印結果：刀,弓
11 
12             //按位與
13             player.equipmentState = Equipment.刀 | Equipment.弓;
14             if (player.equipmentState.Contains(Equipment.刀))
15             {
16                 Console.WriteLine(player.equipmentState.ToString());  //列印結果 ： 刀,弓
17             }
18 
19             //異或
20             player.equipmentState = Equipment.刀 | Equipment.弓;
21             player.equipmentState = player.equipmentState.Remove(Equipment.弓);
22             Console.WriteLine(player.equipmentState.ToString());  //列印結果 ： 刀
23 
24             Console.ReadKey();
25         }
26     }