c# - 如何从其描述中获取枚举值？

Question

我有一个代表系统中所有 Material 装配代码的枚举:

public enum EAssemblyUnit
{
    [Description("UCAL1")]
    eUCAL1,
    [Description("UCAL1-3CP")]
    eUCAL13CP,
    [Description("UCAL40-3CP")]
    eUCAL403CP, // ...
}

在系统另一部分的遗留代码中，我有标有与枚举描述匹配的字符串的对象。给定其中一个字符串，获取枚举值的最简洁方法是什么？我设想的是这样的:

public EAssemblyUnit FromDescription(string AU)
{
    EAssemblyUnit eAU = <value we find with description matching AU>
    return eAU;
}

Answer 1

您需要遍历枚举的所有静态字段(这就是它们在反射中的存储方式)找到每个字段的 Description 属性...当您找到正确的字段时，获取该字段的值.

例如:

public static T GetValue<T>(string description)
{
    foreach (var field in typeof(T).GetFields())
    {
        var descriptions = (DescriptionAttribute[]) 
               field.GetCustomAttributes(typeof(DescriptionAttribute), false);
        if (descriptions.Any(x => x.Description == description))
        {
            return (T) field.GetValue(null);
        }
    }
    throw new SomeException("Description not found");
}

(这是通用的，只是为了使其可重复用于不同的枚举。)

很明显，即使您稍微频繁地这样做，您也希望缓存描述，例如:

public static class DescriptionDictionary<T> where T : struct
{
    private static readonly Dictionary<string, T> Map = 
        new Dictionary<string, T>();

    static DescriptionDictionary()
    {
        if (typeof(T).BaseType != typeof(Enum))
        {
            throw new ArgumentException("Must only use with enums");
        }
        // Could do this with a LINQ query, admittedly...
        foreach (var field in typeof(T).GetFields
                 (BindingFlags.Public | BindingFlags.Static))
        {
            T value = (T) field.GetValue(null);
            foreach (var description in (DescriptionAttribute[]) 
               field.GetCustomAttributes(typeof(DescriptionAttribute), false))
            {
                // TODO: Decide what to do if a description comes up
                // more than once
                Map[description.Description] = value;
            }
        }
    }

    public static T GetValue(string description)
    {
        T ret;
        if (Map.TryGetValue(description, out ret))
        {
            return ret;
        }
        throw new WhateverException("Description not found");
    }
}