C#枚举 Enum

　枚举是直接在命名空间、类或结构中使用 enum 关键字定义的。所有常量名都可以在大括号内声明，并用逗号分隔。

　枚举可以是任何数字数据类型，例如 byte，sbyte，short，ushort，int，uint，long 或 ulong。但是，枚举不能为字符串类型。

1. 枚举（Enum）定义

          public enum WeekDays
           {
               Monday = 0,
               Tuesday = 1,
               Wednesday = 2,
               Thursday = 3,
               Friday = 4,
               Saturday = 5,
               Sunday = 6
           }

    

2. 枚举值获取

          Console.WriteLine(Enum.GetName(typeof(WeekDays), 4));//输出：Friday
          Console.WriteLine(WeekDays.Friday);//输出：Monday
          Console.WriteLine((int) WeekDays.Friday);//输出：4
   
          foreach (var item in Enum.GetValues(typeof(WeekDays)))
          {
              Console.WriteLine((int) item);//循环输出：0,1...
          }
          foreach (var item in Enum.GetNames(typeof(WeekDays)))
          {
              Console.WriteLine(item);//循环输出：Monday，Tuesday...
          }

    

3. Description、EnumMember的使用，完整实列

   using System;
   using System.Collections.Generic;
   using System.ComponentModel;
   using System.Linq;
   using System.Reflection;
   using System.Runtime.Serialization;
   using System.Text;
   using System.Threading.Tasks;
   
   namespace Study
   {
       public class MyEnum
       {
           public enum WeekDays
           {
               [EnumMember(Value = "周一，还有四天.... ")]
               Monday = 0,
               [Description("周二，还有三天....")]
               Tuesday = 1,
               Wednesday = 2,
               Thursday = 3,
               Friday = 4,
               Saturday = 5,
               Sunday = 6
           }
           enum MemberLevel : long
           {
               gold = 2147483648L,
               silver = 232L,
               copper = 10L
           }
   
           public MyEnum()
           {
               Employ(WeekDays.Friday);
           }
           public static void Employ(WeekDays weekDays)
           {
               switch (weekDays)
               {
                   case WeekDays.Monday:
                       break;
                   case WeekDays.Tuesday:
                       break;
                   case WeekDays.Wednesday:
                       break;
                   case WeekDays.Thursday:
                       break;
                   case WeekDays.Friday:
                       Console.WriteLine(Enum.GetName(typeof(WeekDays), 4));//输出：Friday
                       Console.WriteLine(WeekDays.Friday);//输出：Monday
                       Console.WriteLine((int)WeekDays.Friday);//输出：4
                       foreach (var item in Enum.GetValues(typeof(WeekDays)))
                       {
                           Console.WriteLine((int)item);//循环输出：0,1...
                       }
                       foreach (var item in Enum.GetNames(typeof(WeekDays)))
                       {
                           Console.WriteLine(item);//循环输出：Monday，Tuesday...
                       }
                       Console.WriteLine(WeekDays.Monday.ToEnumMemberAttrValue());//输出：周一，还有四天....
                       Console.WriteLine(WeekDays.Tuesday.GetDescription());//输出：周二，还有三天....
                       break;
                   case WeekDays.Saturday:
                       break;
                   case WeekDays.Sunday:
                       break;
                   default:
                       break;
               }
           }
       }
       public static class EnumExt
       {
           public static string ToEnumMemberAttrValue(this Enum @enum)
           {
               var attr =
                   @enum.GetType().GetMember(@enum.ToString()).FirstOrDefault()?.
                       GetCustomAttributes(false).OfType<EnumMemberAttribute>().
                       FirstOrDefault();
               if (attr == null)
                   return @enum.ToString();
               return attr.Value;
   
           }
   
           public static string GetDescription(this Enum @enum, bool isTop = false)
           {
               Type enumType = @enum.GetType();
               DescriptionAttribute attr = null;
               if (isTop)
               {
                   attr = (DescriptionAttribute)Attribute.GetCustomAttribute(enumType, typeof(DescriptionAttribute));
               }
               else
               {
                   // 获取枚举常数名称。
                   string name = Enum.GetName(enumType, @enum);
                   if (name != null)
                   {
                       // 获取枚举字段。
                       FieldInfo fieldInfo = enumType.GetField(name);
                       if (fieldInfo != null)
                       {
                           // 获取描述的属性。
                           attr = Attribute.GetCustomAttribute(fieldInfo, typeof(DescriptionAttribute), false) as DescriptionAttribute;
                       }
                   }
               }
               if (attr != null && !string.IsNullOrEmpty(attr.Description))
                   return attr.Description;
               else
                   return string.Empty;
           }
       }
   }