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

如果0不是合适的默认值，你可以使用组件模型为枚举定义一个变通方法:

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

public static class Utilities
{
    public static TEnum GetDefaultValue<TEnum>() where TEnum : struct
    {
        Type t = typeof(TEnum);
        DefaultValueAttribute[] attributes = (DefaultValueAttribute[])t.GetCustomAttributes(typeof(DefaultValueAttribute), false);
        if (attributes != null &&
            attributes.Length > 0)
        {
            return (TEnum)attributes[0].Value;
        }
        else
        {
            return default(TEnum);
        }
    }
}

然后你可以调用:

Orientation o = Utilities.GetDefaultValue<Orientation>();
System.Diagnostics.Debug.Print(o.ToString());

注意:你需要在文件顶部包含以下一行:

using System.ComponentModel;

这不会改变枚举的实际c#语言默认值，但提供了一种方法来指示(并获得)所需的默认值。

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

如果你将默认enum定义为最小值的enum，你可以使用这个:

public enum MyEnum { His = -1, Hers = -2, Mine = -4, Theirs = -3 }

var firstEnum = ((MyEnum[])Enum.GetValues(typeof(MyEnum)))[0];

firstEnum == Mine.

这并没有假设枚举值为零。

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 
}

enum的默认值是等于0的枚举成员或第一个元素(如果没有指定value)…但我在我的项目中使用枚举遇到了严重的问题，并通过做下面的事情来克服…无论我的需求是如何与阶级水平相关的……

    class CDDtype
    {
        public int Id { get; set; }
        public DDType DDType { get; set; }

        public CDDtype()
        {
            DDType = DDType.None;
        }
    }    


    [DefaultValue(None)]
    public enum DDType
    {       
        None = -1,       
        ON = 0,       
        FC = 1,       
        NC = 2,       
        CC = 3
    }

并得到预期的结果

    CDDtype d1= new CDDtype();
    CDDtype d2 = new CDDtype { Id = 50 };

    Console.Write(d1.DDType);//None
    Console.Write(d2.DDType);//None

现在，如果价值来自DB ....在这种情况下……将值传递给下面的函数，它会将值转换为enum…下面的函数处理了各种场景，它是通用的…相信我，这是非常快.....：）

    public static T ToEnum<T>(this object value)
    {
        //Checking value is null or DBNull
        if (!value.IsNull())
        {
            return (T)Enum.Parse(typeof(T), value.ToStringX());
        }

        //Returanable object
        object ValueToReturn = null;

        //First checking whether any 'DefaultValueAttribute' is present or not
        var DefaultAtt = (from a in typeof(T).CustomAttributes
                          where a.AttributeType == typeof(DefaultValueAttribute)
                          select a).FirstOrNull();

        //If DefaultAttributeValue is present
        if ((!DefaultAtt.IsNull()) && (DefaultAtt.ConstructorArguments.Count == 1))
        {
            ValueToReturn = DefaultAtt.ConstructorArguments[0].Value;
        }

        //If still no value found
        if (ValueToReturn.IsNull())
        {
            //Trying to get the very first property of that enum
            Array Values = Enum.GetValues(typeof(T));

            //getting very first member of this enum
            if (Values.Length > 0)
            {
                ValueToReturn = Values.GetValue(0);
            }
        }

        //If any result found
        if (!ValueToReturn.IsNull())
        {
            return (T)Enum.Parse(typeof(T), ValueToReturn.ToStringX());
        }

        return default(T);
    }