我有以下列举:

public enum AuthenticationMethod
{
    FORMS = 1,
    WINDOWSAUTHENTICATION = 2,
    SINGLESIGNON = 3
}

然而问题是,当我请求AuthenticationMethod时,我需要“FORMS”这个词。表单而不是id

对于这个问题,我找到了以下解决方案(链接):

首先,我需要创建一个自定义属性“StringValue”:

public class StringValue : System.Attribute
{
    private readonly string _value;

    public StringValue(string value)
    {
        _value = value;
    }

    public string Value
    {
        get { return _value; }
    }

}

然后我可以将这个属性添加到我的枚举器中:

public enum AuthenticationMethod
{
    [StringValue("FORMS")]
    FORMS = 1,
    [StringValue("WINDOWS")]
    WINDOWSAUTHENTICATION = 2,
    [StringValue("SSO")]
    SINGLESIGNON = 3
}

当然,我需要一些东西来检索StringValue:

public static class StringEnum
{
    public static string GetStringValue(Enum value)
    {
        string output = null;
        Type type = value.GetType();

        //Check first in our cached results...

        //Look for our 'StringValueAttribute' 

        //in the field's custom attributes

        FieldInfo fi = type.GetField(value.ToString());
        StringValue[] attrs =
           fi.GetCustomAttributes(typeof(StringValue),
                                   false) as StringValue[];
        if (attrs.Length > 0)
        {
            output = attrs[0].Value;
        }

        return output;
    }
}

很好,现在我已经有了工具来获取枚举器的字符串值。 然后我可以这样使用它:

string valueOfAuthenticationMethod = StringEnum.GetStringValue(AuthenticationMethod.FORMS);

好的,现在所有这些工作就像一个魅力,但我发现它有很多工作。我想知道有没有更好的解决办法。

我还尝试了一些字典和静态属性,但这也不是更好。


当前回答

我创建了一个基类,用于在. net中创建字符串值的枚举。它只是一个c#文件,你可以复制粘贴到你的项目中,或者通过名为StringEnum的NuGet包安装。GitHub回购

如果类被注释为xml comment <completitionlist>,智能感知将提示枚举名称。(适用于c#和VB)

类似于普通enum的用法:

///<completionlist cref="HexColor"/> 
class HexColor : StringEnum<HexColor>
{
    public static readonly HexColor Blue = Create("#FF0000");
    public static readonly HexColor Green = Create("#00FF00");
    public static readonly HexColor Red = Create("#000FF");
}
    // Static Parse Method
    HexColor.Parse("#FF0000") // => HexColor.Red
    HexColor.Parse("#ff0000", caseSensitive: false) // => HexColor.Red
    HexColor.Parse("invalid") // => throws InvalidOperationException

    // Static TryParse method.
    HexColor.TryParse("#FF0000") // => HexColor.Red
    HexColor.TryParse("#ff0000", caseSensitive: false) // => HexColor.Red
    HexColor.TryParse("invalid") // => null

    // Parse and TryParse returns the preexistent instances
    object.ReferenceEquals(HexColor.Parse("#FF0000"), HexColor.Red) // => true

    // Conversion from your `StringEnum` to `string`
    string myString1 = HexColor.Red.ToString(); // => "#FF0000"
    string myString2 = HexColor.Red; // => "#FF0000" (implicit cast)

Instalation:

将下面的StringEnum基类粘贴到项目中。(最新版本) 或者安装StringEnum NuGet包,它基于。net Standard 1.0,所以它可以运行在。net Core >= 1.0, . net Framework >= 4.5, Mono >= 4.6等等。

    /// <summary>
    /// Base class for creating string-valued enums in .NET.<br/>
    /// Provides static Parse() and TryParse() methods and implicit cast to string.
    /// </summary>
    /// <example> 
    /// <code>
    /// class Color : StringEnum &lt;Color&gt;
    /// {
    ///     public static readonly Color Blue = Create("Blue");
    ///     public static readonly Color Red = Create("Red");
    ///     public static readonly Color Green = Create("Green");
    /// }
    /// </code>
    /// </example>
    /// <typeparam name="T">The string-valued enum type. (i.e. class Color : StringEnum&lt;Color&gt;)</typeparam>
    public abstract class StringEnum<T> : IEquatable<T> where T : StringEnum<T>, new()
    {
        protected string Value;
        private static Dictionary<string, T> valueDict = new Dictionary<string, T>();
        protected static T Create(string value)
        {
            if (value == null)
                return null; // the null-valued instance is null.

            var result = new T() { Value = value };
            valueDict.Add(value, result);
            return result;
        }

        public static implicit operator string(StringEnum<T> enumValue) => enumValue.Value;
        public override string ToString() => Value;

        public static bool operator !=(StringEnum<T> o1, StringEnum<T> o2) => o1?.Value != o2?.Value;
        public static bool operator ==(StringEnum<T> o1, StringEnum<T> o2) => o1?.Value == o2?.Value;

        public override bool Equals(object other) => this.Value.Equals((other as T)?.Value ?? (other as string));
        bool IEquatable<T>.Equals(T other) => this.Value.Equals(other.Value);
        public override int GetHashCode() => Value.GetHashCode();

        /// <summary>
        /// Parse the <paramref name="value"/> specified and returns a valid <typeparamref name="T"/> or else throws InvalidOperationException.
        /// </summary>
        /// <param name="value">The string value representad by an instance of <typeparamref name="T"/>. Matches by string value, not by the member name.</param>
        /// <param name="caseSensitive">If true, the strings must match case and takes O(log n). False allows different case but is little bit slower (O(n))</param>
        public static T Parse(string value, bool caseSensitive = true)
        {
            var result = TryParse(value, caseSensitive);
            if (result == null)
                throw new InvalidOperationException((value == null ? "null" : $"'{value}'") + $" is not a valid {typeof(T).Name}");

            return result;
        }

        /// <summary>
        /// Parse the <paramref name="value"/> specified and returns a valid <typeparamref name="T"/> or else returns null.
        /// </summary>
        /// <param name="value">The string value representad by an instance of <typeparamref name="T"/>. Matches by string value, not by the member name.</param>
        /// <param name="caseSensitive">If true, the strings must match case. False allows different case but is slower: O(n)</param>
        public static T TryParse(string value, bool caseSensitive = true)
        {
            if (value == null) return null;
            if (valueDict.Count == 0) System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(typeof(T).TypeHandle); // force static fields initialization
            if (caseSensitive)
            {
                if (valueDict.TryGetValue(value, out T item))
                    return item;
                else
                    return null;
            }
            else
            {
                // slower O(n) case insensitive search
                return valueDict.FirstOrDefault(f => f.Key.Equals(value, StringComparison.OrdinalIgnoreCase)).Value;
                // Why Ordinal? => https://esmithy.net/2007/10/15/why-stringcomparisonordinal-is-usually-the-right-choice/
            }
        }
    }

其他回答

使用对象枚举. parse(系统。类型枚举类型,字符串值,bool ignoreCase);从http://blogs.msdn.com/b/tims/archive/2004/04/02/106310.aspx获取

我如何解决这个扩展方法:

using System.ComponentModel;
public static string GetDescription(this Enum value)
{
    var descriptionAttribute = (DescriptionAttribute)value.GetType()
        .GetField(value.ToString())
        .GetCustomAttributes(false)
        .Where(a => a is DescriptionAttribute)
        .FirstOrDefault();

    return descriptionAttribute != null ? descriptionAttribute.Description : value.ToString();
}

枚举:

public enum OrderType
{
    None = 0,
    [Description("New Card")]
    NewCard = 1,
    [Description("Reload")]
    Refill = 2
}

用法(其中o.OrderType是一个与enum同名的属性):

o.OrderType.GetDescription()

这给了我一个字符串的“新卡”或“重载”,而不是实际的enum值NewCard和重新填充。

对于较大的字符串enum集,列出的示例可能会变得令人厌烦。如果您想要一个状态代码列表,或者其他基于字符串的枚举列表,那么属性系统使用起来很麻烦,而带有自身实例的静态类配置起来也很麻烦。对于我自己的解决方案,我使用了T4模板,以便更容易地使用字符串支持的枚举。结果与HttpMethod类的工作方式类似。

你可以这样使用它:

    string statusCode = ResponseStatusCode.SUCCESS; // Automatically converts to string when needed
    ResponseStatusCode codeByValueOf = ResponseStatusCode.ValueOf(statusCode); // Returns null if not found

    // Implements TypeConverter so you can use it with string conversion methods.
    var converter = System.ComponentModel.TypeDescriptor.GetConverter(typeof(ResponseStatusCode));
    ResponseStatusCode code = (ResponseStatusCode) converter.ConvertFromInvariantString(statusCode);

    // You can get a full list of the values
    bool canIterateOverValues = ResponseStatusCode.Values.Any(); 

    // Comparisons are by value of the "Name" property. Not by memory pointer location.
    bool implementsByValueEqualsEqualsOperator = "SUCCESS" == ResponseStatusCode.SUCCESS; 

你从Enum开始。tt文件。

<#@ include file="StringEnum.ttinclude" #>


<#+
public static class Configuration
{
    public static readonly string Namespace = "YourName.Space";
    public static readonly string EnumName = "ResponseStatusCode";
    public static readonly bool IncludeComments = true;

    public static readonly object Nodes = new
    {
        SUCCESS = "The response was successful.",
        NON_SUCCESS = "The request was not successful.",
        RESOURCE_IS_DISCONTINUED = "The resource requested has been discontinued and can no longer be accessed."
    };
}
#>

然后,添加StringEnum。ttinclude文件。

<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ assembly name="System.Core" #>
<#@ import namespace="System" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Reflection" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ output extension=".cs" #>
<#@ CleanupBehavior processor="T4VSHost" CleanupAfterProcessingtemplate="true" #>

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel;
using System.Globalization;

namespace <#= Configuration.Namespace #>
{
    /// <summary>
    /// TypeConverter implementations allow you to use features like string.ToNullable(T).
    /// </summary>
    public class <#= Configuration.EnumName #>TypeConverter : TypeConverter
    {
        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
        {
            return sourceType == typeof(string) || base.CanConvertFrom(context, sourceType);
        }

        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
        {
            var casted = value as string;

            if (casted != null)
            {
                var result = <#= Configuration.EnumName #>.ValueOf(casted);
                if (result != null)
                {
                    return result;
                }
            }

            return base.ConvertFrom(context, culture, value);
        }

        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
        {
            var casted = value as <#= Configuration.EnumName #>;
            if (casted != null && destinationType == typeof(string))
            {
                return casted.ToString();
            }

            return base.ConvertTo(context, culture, value, destinationType);
        }
    }

    [TypeConverter(typeof(<#= Configuration.EnumName #>TypeConverter))]
    public class <#= Configuration.EnumName #> : IEquatable<<#= Configuration.EnumName #>>
    {
//---------------------------------------------------------------------------------------------------
// V A L U E S _ L I S T
//---------------------------------------------------------------------------------------------------
<# Write(Helpers.PrintEnumProperties(Configuration.Nodes)); #>

        private static List<<#= Configuration.EnumName #>> _list { get; set; } = null;
        public static List<<#= Configuration.EnumName #>> ToList()
        {
            if (_list == null)
            {
                _list = typeof(<#= Configuration.EnumName #>).GetFields().Where(x => x.IsStatic && x.IsPublic && x.FieldType == typeof(<#= Configuration.EnumName #>))
                    .Select(x => x.GetValue(null)).OfType<<#= Configuration.EnumName #>>().ToList();
            }

            return _list;
        }

        public static List<<#= Configuration.EnumName #>> Values()
        {
            return ToList();
        }

        /// <summary>
        /// Returns the enum value based on the matching Name of the enum. Case-insensitive search.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static <#= Configuration.EnumName #> ValueOf(string key)
        {
            return ToList().FirstOrDefault(x => string.Compare(x.Name, key, true) == 0);
        }


//---------------------------------------------------------------------------------------------------
// I N S T A N C E _ D E F I N I T I O N
//---------------------------------------------------------------------------------------------------      
        public string Name { get; private set; }
        public string Description { get; private set; }
        public override string ToString() { return this.Name; }

        /// <summary>
        /// Implcitly converts to string.
        /// </summary>
        /// <param name="d"></param>
        public static implicit operator string(<#= Configuration.EnumName #> d)
        {
            return d.ToString();
        }

        /// <summary>
        /// Compares based on the == method. Handles nulls gracefully.
        /// </summary>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <returns></returns>
        public static bool operator !=(<#= Configuration.EnumName #> a, <#= Configuration.EnumName #> b)
        {
            return !(a == b);
        }

        /// <summary>
        /// Compares based on the .Equals method. Handles nulls gracefully.
        /// </summary>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <returns></returns>
        public static bool operator ==(<#= Configuration.EnumName #> a, <#= Configuration.EnumName #> b)
        {
            return a?.ToString() == b?.ToString();
        }

        /// <summary>
        /// Compares based on the .ToString() method
        /// </summary>
        /// <param name="o"></param>
        /// <returns></returns>
        public override bool Equals(object o)
        {
            return this.ToString() == o?.ToString();
        }

        /// <summary>
        /// Compares based on the .ToString() method
        /// </summary>
        /// <param name="other"></param>
        /// <returns></returns>
        public bool Equals(<#= Configuration.EnumName #> other)
        {
            return this.ToString() == other?.ToString();
        }

        /// <summary>
        /// Compares based on the .Name property
        /// </summary>
        /// <returns></returns>
        public override int GetHashCode()
        {
            return this.Name.GetHashCode();
        }
    }
}

<#+

public static class Helpers
{
        public static string PrintEnumProperties(object nodes)
        {
            string o = "";
            Type nodesTp = Configuration.Nodes.GetType();
            PropertyInfo[] props = nodesTp.GetProperties().OrderBy(p => p.Name).ToArray();

            for(int i = 0; i < props.Length; i++)
            {
                var prop = props[i];
                if (Configuration.IncludeComments)
                {
                    o += "\r\n\r\n";
                    o += "\r\n        ///<summary>";
                    o += "\r\n        /// "+Helpers.PrintPropertyValue(prop, Configuration.Nodes);
                    o += "\r\n        ///</summary>";
                }

                o += "\r\n        public static readonly "+Configuration.EnumName+" "+prop.Name+ " = new "+Configuration.EnumName+"(){ Name = \""+prop.Name+"\", Description = "+Helpers.PrintPropertyValue(prop, Configuration.Nodes)+ "};";
            }

            o += "\r\n\r\n";

            return o;
        }

        private static Dictionary<string, string> GetValuesMap()
        {
            Type nodesTp = Configuration.Nodes.GetType();
            PropertyInfo[] props= nodesTp.GetProperties();
            var dic = new Dictionary<string,string>();
            for(int i = 0; i < props.Length; i++)
            {
                var prop = nodesTp.GetProperties()[i];
                dic[prop.Name] = prop.GetValue(Configuration.Nodes).ToString();
            }
            return dic;
        }

        public static string PrintMasterValuesMap(object nodes)
        {
            Type nodesTp = Configuration.Nodes.GetType();
            PropertyInfo[] props= nodesTp.GetProperties();
            string o = "        private static readonly Dictionary<string, string> ValuesMap = new Dictionary<string, string>()\r\n        {";
            for(int i = 0; i < props.Length; i++)
            {
                var prop = nodesTp.GetProperties()[i];
                o += "\r\n            { \""+prop.Name+"\", "+(Helpers.PrintPropertyValue(prop,Configuration.Nodes)+" },");
            }
            o += ("\r\n        };\r\n");

            return o;
        }


        public static string PrintPropertyValue(PropertyInfo prop, object objInstance)
        {
            switch(prop.PropertyType.ToString()){
                case "System.Double":
                    return prop.GetValue(objInstance).ToString()+"D";
                case "System.Float":
                    return prop.GetValue(objInstance).ToString()+"F";
                case "System.Decimal":
                    return prop.GetValue(objInstance).ToString()+"M";
                case "System.Long":
                    return prop.GetValue(objInstance).ToString()+"L";
                case "System.Boolean":
                case "System.Int16":
                case "System.Int32":
                    return prop.GetValue(objInstance).ToString().ToLowerInvariant();
                case "System.String":
                    return "\""+prop.GetValue(objInstance)+"\"";
            }

            return prop.GetValue(objInstance).ToString();
        }

        public static string _ (int numSpaces)
        {
            string o = "";
            for(int i = 0; i < numSpaces; i++){
                o += " ";
            }

            return o;
        }
}
#>

最后,重新编译Enum。Tt文件,输出如下所示:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Linq;
using System.Collections.Generic;

namespace YourName.Space
{
    public class ResponseStatusCode
    {
//---------------------------------------------------------------------------------------------------
// V A L U E S _ L I S T 
//---------------------------------------------------------------------------------------------------



        ///<summary>
        /// "The response was successful."
        ///</summary>
        public static readonly ResponseStatusCode SUCCESS = new ResponseStatusCode(){ Name = "SUCCESS", Description = "The response was successful."};


        ///<summary>
        /// "The request was not successful."
        ///</summary>
        public static readonly ResponseStatusCode NON_SUCCESS = new ResponseStatusCode(){ Name = "NON_SUCCESS", Description = "The request was not successful."};


        ///<summary>
        /// "The resource requested has been discontinued and can no longer be accessed."
        ///</summary>
        public static readonly ResponseStatusCode RESOURCE_IS_DISCONTINUED = new ResponseStatusCode(){ Name = "RESOURCE_IS_DISCONTINUED", Description = "The resource requested has been discontinued and can no longer be accessed."};


        private static List<ResponseStatusCode> _list { get; set; } = null;
        public static List<ResponseStatusCode> ToList()
        {
            if (_list == null)
            {
                _list = typeof(ResponseStatusCode).GetFields().Where(x => x.IsStatic && x.IsPublic && x.FieldType == typeof(ResponseStatusCode))
                    .Select(x => x.GetValue(null)).OfType<ResponseStatusCode>().ToList();
            }

            return _list;
        }

        public static List<ResponseStatusCode> Values()
        {
            return ToList();
        }

        /// <summary>
        /// Returns the enum value based on the matching Name of the enum. Case-insensitive search.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static ResponseStatusCode ValueOf(string key)
        {
            return ToList().FirstOrDefault(x => string.Compare(x.Name, key, true) == 0);
        }


//---------------------------------------------------------------------------------------------------
// I N S T A N C E _ D E F I N I T I O N 
//---------------------------------------------------------------------------------------------------       
        public string Name { get; set; }
        public string Description { get; set; }
        public override string ToString() { return this.Name; }

        /// <summary>
        /// Implcitly converts to string.
        /// </summary>
        /// <param name="d"></param>
        public static implicit operator string(ResponseStatusCode d)
        {
            return d.ToString();
        }

        /// <summary>
        /// Compares based on the == method. Handles nulls gracefully.
        /// </summary>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <returns></returns>
        public static bool operator !=(ResponseStatusCode a, ResponseStatusCode b)
        {
            return !(a == b);
        }

        /// <summary>
        /// Compares based on the .Equals method. Handles nulls gracefully.
        /// </summary>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <returns></returns>
        public static bool operator ==(ResponseStatusCode a, ResponseStatusCode b)
        {
            return a?.ToString() == b?.ToString();
        }

        /// <summary>
        /// Compares based on the .ToString() method
        /// </summary>
        /// <param name="o"></param>
        /// <returns></returns>
        public override bool Equals(object o)
        {
            return this.ToString() == o?.ToString();
        }

        /// <summary>
        /// Compares based on the .Name property
        /// </summary>
        /// <returns></returns>
        public override int GetHashCode()
        {
            return this.Name.GetHashCode();
        }
    }
}

不幸的是,在枚举上获取属性的反射非常慢:

看这个问题:有人知道一种快速获取枚举值的自定义属性的方法吗?

. tostring()在枚举上也相当慢。

你可以为枚举写扩展方法:

public static string GetName( this MyEnum input ) {
    switch ( input ) {
        case MyEnum.WINDOWSAUTHENTICATION:
            return "Windows";
        //and so on
    }
}

这不是很好,但是很快,而且不需要对属性或字段名进行反射。


c# 6更新

如果你可以使用c# 6,那么操作符的新名称适用于枚举,因此nameof(myenume .WINDOWSAUTHENTICATION)将在编译时转换为“WINDOWSAUTHENTICATION”,使其成为获取枚举名称的最快方式。

注意,这将显式枚举转换为内联常量,因此它不适用于变量中的枚举。所以:

nameof(AuthenticationMethod.FORMS) == "FORMS"

但是…

var myMethod = AuthenticationMethod.FORMS;
nameof(myMethod) == "myMethod"

我使用系统中的Description属性。ComponentModel名称空间。简单地装饰枚举,然后使用下面的代码来检索它:

public static string GetDescription<T>(this object enumerationValue)
            where T : struct
        {
            Type type = enumerationValue.GetType();
            if (!type.IsEnum)
            {
                throw new ArgumentException("EnumerationValue must be of Enum type", "enumerationValue");
            }

            //Tries to find a DescriptionAttribute for a potential friendly name
            //for the enum
            MemberInfo[] memberInfo = type.GetMember(enumerationValue.ToString());
            if (memberInfo != null && memberInfo.Length > 0)
            {
                object[] attrs = memberInfo[0].GetCustomAttributes(typeof(DescriptionAttribute), false);

                if (attrs != null && attrs.Length > 0)
                {
                    //Pull out the description value
                    return ((DescriptionAttribute)attrs[0]).Description;
                }
            }
            //If we have no description attribute, just return the ToString of the enum
            return enumerationValue.ToString();

        }

举个例子:

public enum Cycle : int
{        
   [Description("Daily Cycle")]
   Daily = 1,
   Weekly,
   Monthly
}

这段代码很好地满足了不需要“友好名称”的枚举,只返回枚举的. tostring()。