c# - How to get all descriptions of enum values with reflection?

Question

So I need to get a List<string> from my enum

Here is what I have done so far:

enum definition

    [Flags]
    public enum ContractorType
    {
        [Description("Recipient")]
        RECIPIENT = 1,
        [Description("Deliver")]
        DELIVER = 2,
        [Description("Recipient / Deliver")]
        RECIPIENT_DELIVER = 4
    }

HelperClass with method to do what I need:

public static class EnumUtils
{
    public static IEnumerable<string> GetDescrptions(Type enumerator)
    {
        FieldInfo[] fi = enumerator.GetFields();

        List<DescriptionAttribute> attributes = new List<DescriptionAttribute>();
        foreach (var i in fi)
        {
            try
            {
                yield return attributes.Add(((DescriptionAttribute[])i.GetCustomAttributes(
                    typeof(DescriptionAttribute),
                    false))[0]);
            }
            catch { }
        }
        return new List<string>{"empty"};
    }
}

Now in the line where I yield values, I got a NullReferenceException. Did I miss something? The syntax looks all right to me, but maybe I overlooked something?

Edit: I'm using .net Framework 4.0 here.

score 6 · Accepted Answer

这种通用静态方法可以很好地获取枚举类型 T 的每个值的描述列表：

public static IEnumerable<string> GetDescriptions<T>()
{
    var attributes = typeof(T).GetMembers()
        .SelectMany(member => member.GetCustomAttributes(typeof (DescriptionAttribute), true).Cast<DescriptionAttribute>())
        .ToList();

    return attributes.Select(x => x.Description);
}

score 4 · Accepted Answer

这是一个可重复使用的小型解决方案。这是一个抽象类，它将从类型T中提取类型K的所有属性。

abstract class AbstractAttributes<T, K>
{
    protected List<K> Attributes = new List<K>();

    public AbstractAttributes()
    {
        foreach (var member in typeof(T).GetMembers())
        {
            foreach (K attribute in member.GetCustomAttributes(typeof(K), true)) 
                Attributes.Add(attribute);                
        }
    }
}

如果我们现在只想提取DescriptionAttribute类型的属性，我们将使用以下类。

class DescriptionAttributes<T> : AbstractAttributes<T, DescriptionAttribute>
{
    public List<string> Descriptions { get; set; }

    public DescriptionAttributes()
    {
        Descriptions = Attributes.Select(x => x.Description).ToList();
    }
}

此类将仅从DescriptionAttributetype 中提取 type 的属性T。但是要在您的上下文中实际使用此类，您只需执行以下操作。

new DescriptionAttributes<ContractorType>().Descriptions.ForEach(x => Console.WriteLine(x));

这行代码将写出您在 type 属性中用作参数的所有描述DescriptionAttribute。如果您需要提取一些其他属性，只需创建一个派生自该类的新类并使用适当的属性AbstractAttributes<T, K>关闭其类型。K

score 3 · Accepted Answer

我创建了这些扩展方法

public static class EnumExtender
{
    public static string GetDescription(this Enum enumValue)
    {
        string output = null;
        Type type = enumValue.GetType();
        FieldInfo fi = type.GetField(enumValue.ToString());
        var attrs = fi.GetCustomAttributes(typeof(DescriptionAttribute), false) as DescriptionAttribute[];
        if (attrs.Length > 0) output = attrs[0].Description;
        return output;
    }

    public static IDictionary<T, string> GetEnumValuesWithDescription<T>(this Type type) where T : struct, IConvertible
    {
        if (!type.IsEnum)
        {
            throw new ArgumentException("T must be an enumerated type");
        }

        return type.GetEnumValues()
                .OfType<T>()
                .ToDictionary(
                    key => key,
                    val => (val as Enum).GetDescription()
                );
    }
}

用法

var stuff = typeof(TestEnum).GetEnumValuesWithDescription<TestEnum>();

将返回一个Dictionary<TestEnum, string>值作为键和描述作为值。如果您只想要一个列表，您可以更改.ToDictionary为

.Select(o => (o as Enum).GetDescription())
.ToList()

score 2 · Accepted Answer

您需要DescriptionAttribute在每个字段上找到（如果存在），然后检索Description属性，例如

return enumType.GetFields()
                .Select(f => (DescriptionAttribute)f.GetCustomAttribute(typeof(DescriptionAttribute)))
                .Where(a => a != null)
                .Select(a => a.Description)

如果您可以在一个字段上有多个描述，您可以执行以下操作：

FieldInfo[] fields = enumType.GetFields();
foreach(FieldInfo field in fields)
{
    var descriptionAttributes = field.GetCustomAttributes(false).OfType<DescriptionAttribute>();
    foreach(var descAttr in descriptionAttributes)
    {
        yield return descAttr.Description;
    }
}

这与您现有的方法更相似。

score 0 · Accepted Answer

这是字典而不是列表
但是是我使用的东西

using System.ComponentModel;
using System.Reflection;
using MyExtensions;

namespace MyExtensions
{
    public static class Extension
    {
        public static string GetDescriptionName(this Enum value)
        {
            Type type = value.GetType();
            string name = Enum.GetName(type, value);
            if (name == null)
                return null;
            else
            {
                FieldInfo field = type.GetField(name);
                if (field == null)
                    return name;
                else
                {
                    DescriptionAttribute attr =
                            Attribute.GetCustomAttribute(field,
                                typeof(DescriptionAttribute)) as DescriptionAttribute;
                    if (attr == null)
                        return name;
                    else
                        return attr.Description;
                }
            }
        }
    }
}

namespace EnumDescription
{
    class Program
    {
        public enum enumDateCond : byte 
        {
            [Description("Empty")]
            Null = 0,
            [Description("Not Empty")]
            NotNull = 1,
            EQ = 2, 
            LT = 3, 
            LE = 4, 
            GE = 14, 
            GT = 15 
        };
        static void Main(string[] args)
        {
            enumDateCond x = enumDateCond.Null;
            string description = x.GetDescriptionName();
            foreach (enumDateCond enm in Enum.GetValues(typeof(enumDateCond)))
            {
                description = enm.GetDescriptionName();
                Console.WriteLine(description);
            }
            Console.WriteLine("Dictionary");
            Dictionary<enumDateCond, string> DLenumDateCond = EnumToDictionary<enumDateCond>();
            foreach(enumDateCond key in DLenumDateCond.Keys)
            {
                Console.WriteLine(key.ToString() + " " + DLenumDateCond[key]);
            }
        }
        public static Dictionary<T, string> EnumToDictionary<T>()
            where T : struct
        {
            Type enumType = typeof(T);

            // Can't use generic type constraints on value types,
            // so have to do check like this
            if (enumType.BaseType != typeof(Enum))
                throw new ArgumentException("T must be of type System.Enum");

            Dictionary<T, string> enumDL = new Dictionary<T, string>();
            foreach (T enm in Enum.GetValues(enumType))
            {
                string name = Enum.GetName(enumType, enm);
                if (name != null)
                {
                    FieldInfo field = enumType.GetField(name);
                    if (field != null)
                    {
                        DescriptionAttribute attr =
                                Attribute.GetCustomAttribute(field,
                                    typeof(DescriptionAttribute)) as DescriptionAttribute;
                        if (attr != null)
                            name = attr.Description;
                    }
                }
                enumDL.Add(enm, name);
            }
            return enumDL;
        }
    }
}

score 0 · Accepted Answer

你可以试试这个

public string ContractorTypeDescription(Enum ContractorType)
{
    FieldInfo fi = ContractorType.GetType().GetField(ContractorType.ToString());
    var attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
    if (attributes.Length > 0)
    {
        return attributes[0].Description;
    }
    else
    {
        return ContractorType.ToString();
    }
}

score 0 · Accepted Answer

它认为这可以解决您的问题。如果未实现，您可以返回null或异常。这取决于你需要什么。

public DescriptionAttribute GetDescription(ContractorType contractorType)
{
     MemberInfo memberInfo = typeof(ContractorType).GetMember(contractorType.ToString())
                                          .FirstOrDefault();

     if (memberInfo != null)
    {
         DescriptionAttribute attribute = (DescriptionAttribute) 
                 memberInfo.GetCustomAttributes(typeof(DescriptionAttribute), false)
                           .FirstOrDefault();
         return attribute;
    }

    //return null;
    //or

    throw new NotImplementedException("There is no description for this enum");
}

所以你会像这样使用它：

DescriptionAttribute attribute = GetDescription(ContractorType.RECIPIENT);

抱歉，我没有阅读您的问题。下面是一些可用于获取所有描述字符串的代码：

 public IEnumerable<string> GetAllDescriptionInText()
 {
     List<string> descList = new List<string>();
     foreach (DescriptionAttribute desc in Enum.GetValues(typeof(DescriptionAttribute)))
     {
         descList.Add(GetDescription(desc).Value);
     }
     return descList;
 }

c# - How to get all descriptions of enum values with reflection?

7 回答 7

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