Enum的字符串表示形式

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

当我遇到这样的情况时，我提出下面的解决方案。

作为一个消费阶级，你可以有

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

namespace MyApp.Dictionaries
{
    class Greek
    {

        public static readonly string Alpha = "Alpha";
        public static readonly string Beta = "Beta";
        public static readonly string Gamma = "Gamma";
        public static readonly string Delta = "Delta";


        private static readonly BiDictionary<int, string> Dictionary = new BiDictionary<int, string>();


        static Greek() {
            Dictionary.Add(1, Alpha);
            Dictionary.Add(2, Beta);
            Dictionary.Add(3, Gamma);
            Dictionary.Add(4, Delta);
        }

        public static string getById(int id){
            return Dictionary.GetByFirst(id);
        }

        public static int getByValue(string value)
        {
            return Dictionary.GetBySecond(value);
        }

    }
}

使用双向字典: 基于此(https://stackoverflow.com/a/255638/986160)，假设键将与字典中的单个值相关联，类似于(https://stackoverflow.com/a/255630/986160)，但更优雅一些。这个字典也是可枚举的，你可以在整型和字符串之间来回切换。此外，除了这个类，你的代码库中不需要有任何字符串。

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

namespace MyApp.Dictionaries
{

    class BiDictionary<TFirst, TSecond> : IEnumerable
    {
        IDictionary<TFirst, TSecond> firstToSecond = new Dictionary<TFirst, TSecond>();
        IDictionary<TSecond, TFirst> secondToFirst = new Dictionary<TSecond, TFirst>();

        public void Add(TFirst first, TSecond second)
        {
            firstToSecond.Add(first, second);
            secondToFirst.Add(second, first);
        }

        public TSecond this[TFirst first]
        {
            get { return GetByFirst(first); }
        }

        public TFirst this[TSecond second]
        {
            get { return GetBySecond(second); }
        }

        public TSecond GetByFirst(TFirst first)
        {
            return firstToSecond[first];
        }

        public TFirst GetBySecond(TSecond second)
        {
            return secondToFirst[second];
        }

        public IEnumerator GetEnumerator()
        {
            return GetFirstEnumerator();
        }

        public IEnumerator GetFirstEnumerator()
        {
            return firstToSecond.GetEnumerator();
        }

        public IEnumerator GetSecondEnumerator()
        {
            return secondToFirst.GetEnumerator();
        }
    }
}

2014-11-03 22:03:02

其他回答

在你的问题中，你从未说过你实际上需要枚举的数值。

如果你不这样做，只是需要一个string类型的枚举(这不是一个整型，所以不能是enum的基)这里有一个方法:

    static class AuthenticationMethod
    {
        public static readonly string
            FORMS = "Forms",
            WINDOWSAUTHENTICATION = "WindowsAuthentication";
    }

您可以使用与enum相同的语法来引用它

if (bla == AuthenticationMethod.FORMS)

它将比使用数值(比较字符串而不是数字)稍微慢一些，但从好的方面来看，它不使用反射(慢)来访问字符串。

2015-04-17 21:50:01

选项1:

public sealed class FormsAuth
{
     public override string ToString{return "Forms Authtentication";}
}
public sealed class WindowsAuth
{
     public override string ToString{return "Windows Authtentication";}
}

public sealed class SsoAuth
{
     public override string ToString{return "SSO";}
}

然后

object auth = new SsoAuth(); //or whatever

//...
//...
// blablabla

DoSomethingWithTheAuth(auth.ToString());

选项2:

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

public class MyClass
{
    private Dictionary<AuthenticationMethod, String> map = new Dictionary<AuthenticationMethod, String>();
    public MyClass()
    {
         map.Add(AuthenticationMethod.FORMS,"Forms Authentication");
         map.Add(AuthenticationMethod.WINDOWSAUTHENTICATION ,"Windows Authentication");
         map.Add(AuthenticationMethod.SINGLESIGNON ,"SSo Authentication");
    }
}

2009-01-08 15:41:08

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/
            }
        }
    }

2019-10-24 04:01:43

我的变体

public struct Colors
{
    private String current;

    private static string red = "#ff0000";
    private static string green = "#00ff00";
    private static string blue = "#0000ff";

    private static IList<String> possibleColors; 

    public static Colors Red { get { return (Colors) red; } }
    public static Colors Green { get { return (Colors) green; } }
    public static Colors Blue { get { return (Colors) blue; } }

    static Colors()
    {
        possibleColors = new List<string>() {red, green, blue};
    }

    public static explicit operator String(Colors value)
    {
        return value.current;
    }

    public static explicit operator Colors(String value)
    {
        if (!possibleColors.Contains(value))
        {
            throw new InvalidCastException();
        }

        Colors color = new Colors();
        color.current = value;
        return color;
    }

    public static bool operator ==(Colors left, Colors right)
    {
        return left.current == right.current;
    }

    public static bool operator !=(Colors left, Colors right)
    {
        return left.current != right.current;
    }

    public bool Equals(Colors other)
    {
        return Equals(other.current, current);
    }

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (obj.GetType() != typeof(Colors)) return false;
        return Equals((Colors)obj);
    }

    public override int GetHashCode()
    {
        return (current != null ? current.GetHashCode() : 0);
    }

    public override string ToString()
    {
        return current;
    }
}

代码看起来有点丑，但是这个结构体的用法很有代表性。

Colors color1 = Colors.Red;
Console.WriteLine(color1); // #ff0000

Colors color2 = (Colors) "#00ff00";
Console.WriteLine(color2); // #00ff00

// Colors color3 = "#0000ff"; // Compilation error
// String color4 = Colors.Red; // Compilation error

Colors color5 = (Colors)"#ff0000";
Console.WriteLine(color1 == color5); // True

Colors color6 = (Colors)"#00ff00";
Console.WriteLine(color1 == color6); // False

此外，我认为，如果需要大量这样的枚举，可能会使用代码生成(例如T4)。

2012-02-01 16:00:37

我真的很喜欢Jakub Šturc的答案，但它的缺点是不能与开关case语句一起使用。下面是他的回答的一个稍微修改的版本，可以与switch语句一起使用:

public sealed class AuthenticationMethod
{
    #region This code never needs to change.
    private readonly string _name;
    public readonly Values Value;

    private AuthenticationMethod(Values value, String name){
        this._name = name;
        this.Value = value;
    }

    public override String ToString(){
        return _name;
    }
    #endregion

    public enum Values
    {
        Forms = 1,
        Windows = 2,
        SSN = 3
    }

    public static readonly AuthenticationMethod FORMS = new AuthenticationMethod (Values.Forms, "FORMS");
    public static readonly AuthenticationMethod WINDOWSAUTHENTICATION = new AuthenticationMethod (Values.Windows, "WINDOWS");
    public static readonly AuthenticationMethod SINGLESIGNON = new AuthenticationMethod (Values.SSN, "SSN");
}

所以你得到了Jakub Šturc的答案的所有好处，另外我们可以像这样使用switch语句:

var authenticationMethodVariable = AuthenticationMethod.FORMS;  // Set the "enum" value we want to use.
var methodName = authenticationMethodVariable.ToString();       // Get the user-friendly "name" of the "enum" value.

// Perform logic based on which "enum" value was chosen.
switch (authenticationMethodVariable.Value)
{
    case authenticationMethodVariable.Values.Forms: // Do something
        break;
    case authenticationMethodVariable.Values.Windows: // Do something
        break;
    case authenticationMethodVariable.Values.SSN: // Do something
        break;      
}

2014-01-20 21:13:47

Enum的字符串表示形式

推荐文章

最新文章

标签