enum(实际上，任何值类型)的默认值是0——即使这不是该enum的有效值。这是无法改变的。

还有一种方法可能会有帮助——使用某种“别名”。 例如:

public enum Status
{
    New = 10,
    Old = 20,
    Actual = 30,

    // Use Status.Default to specify default status in your code. 
    Default = New 
}

实际上，枚举的默认值是枚举中第一个值为0的元素。

例如:

public enum Animals
{
    Cat,
    Dog,
    Pony = 0,
}
//its value will actually be Cat not Pony unless you assign a non zero value to Cat.
Animals animal;

在这种情况下，不要依赖enum值。设None为0作为默认值。

// Remove all the values from the enum
enum Orientation
{
    None, // = 0 Putting None as the first enum value will make it the default
    North, // = 1
    East, // = 2
    South, // = 3
    West // = 4
}

然后使用一种方法来获得魔数。你可以引入一个扩展方法并像这样使用它:

// Extension Methods are added by adding a using to the namespace
using ProjectName.Extensions;

Orientation.North.ToMagicNumber();

下面是代码:

namespace ProjectName.Extensions
{
    public static class OrientationExtensions 
    {
        public static int ToMagicNumber(this Orientation orientation) => oritentation switch
        {
            case None  => -1,
            case North => 0,
            case East  => 1,
            case South => 2,
            case West  => 3,
            _          => throw new ArgumentOutOfRangeException(nameof(orientation), $"Not expected orientation value: {orientation}")
        };
    }
}

[DefaultValue(None)]
public enum Orientation
{
    None = -1,
    North = 0,
    East = 1,
    South = 2,
    West = 3
}

然后在代码中可以使用

public Orientation GetDefaultOrientation()
{
   return default(Orientation);
} 

你不能，但如果你想的话，你可以耍点小把戏。:)

    public struct Orientation
    {
        ...
        public static Orientation None = -1;
        public static Orientation North = 0;
        public static Orientation East = 1;
        public static Orientation South = 2;
        public static Orientation West = 3;
    }

此结构体的用法为简单enum。 你可以创建p.a == Orientation。默认为East(或您想要的任何值) 要使用这个技巧本身，您需要通过代码从int转换。 实现如下:

        #region ConvertingToEnum
        private int val;
        static Dictionary<int, string> dict = null;

        public Orientation(int val)
        {
            this.val = val;
        }

        public static implicit operator Orientation(int value)
        {
            return new Orientation(value - 1);
        }

        public static bool operator ==(Orientation a, Orientation b)
        {
            return a.val == b.val;
        }

        public static bool operator !=(Orientation a, Orientation b)
        {
            return a.val != b.val;
        }

        public override string ToString()
        {
            if (dict == null)
                InitializeDict();
            if (dict.ContainsKey(val))
                return dict[val];
            return val.ToString();
        }

        private void InitializeDict()
        {
            dict = new Dictionary<int, string>();
            foreach (var fields in GetType().GetFields(BindingFlags.Public | BindingFlags.Static))
            {
                dict.Add(((Orientation)fields.GetValue(null)).val, fields.Name);
            }
        } 
        #endregion