从描述属性获取枚举[重复]

Question

可能重复：
Finding an enum value by its Description Attribute

我有一个通用扩展方法，它从Enum 获取Description 属性：

enum Animal
{
    [Description("")]
    NotSet = 0,

    [Description("Giant Panda")]
    GiantPanda = 1,

    [Description("Lesser Spotted Anteater")]
    LesserSpottedAnteater = 2
}

public static string GetDescription(this Enum value)
{            
    FieldInfo field = value.GetType().GetField(value.ToString());

    DescriptionAttribute attribute
            = Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute))
                as DescriptionAttribute;

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

所以我可以...

string myAnimal = Animal.GiantPanda.GetDescription(); // = "Giant Panda"

现在，我正在尝试在另一个方向上计算出等效的功能，例如...

Animal a = (Animal)Enum.GetValueFromDescription("Giant Panda", typeof(Animal));

Answer 1

public static class EnumEx
{
    public static T GetValueFromDescription<T>(string description) where T : Enum
    {
        foreach(var field in typeof(T).GetFields())
        {
            if (Attribute.GetCustomAttribute(field,
            typeof(DescriptionAttribute)) is DescriptionAttribute attribute)
            {
                if (attribute.Description == description)
                    return (T)field.GetValue(null);
            }
            else
            {
                if (field.Name == description)
                    return (T)field.GetValue(null);
            }
        }

        throw new ArgumentException("Not found.", nameof(description));
        // Or return default(T);
    }
}

用法：

var panda = EnumEx.GetValueFromDescription<Animal>("Giant Panda");

Answer 2

而不是扩展方法，只需尝试几个静态方法

public static class Utility
{
    public static string GetDescriptionFromEnumValue(Enum value)
    {
        DescriptionAttribute attribute = value.GetType()
            .GetField(value.ToString())
            .GetCustomAttributes(typeof (DescriptionAttribute), false)
            .SingleOrDefault() as DescriptionAttribute;
        return attribute == null ? value.ToString() : attribute.Description;
    }

    public static T GetEnumValueFromDescription<T>(string description)
    {
        var type = typeof(T);
        if (!type.IsEnum)
            throw new ArgumentException();
        FieldInfo[] fields = type.GetFields();
        var field = fields
                        .SelectMany(f => f.GetCustomAttributes(
                            typeof(DescriptionAttribute), false), (
                                f, a) => new { Field = f, Att = a })
                        .Where(a => ((DescriptionAttribute)a.Att)
                            .Description == description).SingleOrDefault();
        return field == null ? default(T) : (T)field.Field.GetRawConstantValue();
    }
}

在这里使用

var result1 = Utility.GetDescriptionFromEnumValue(
    Animal.GiantPanda);
var result2 = Utility.GetEnumValueFromDescription<Animal>(
    "Lesser Spotted Anteater");

Answer 3

除非您有 Web 服务，否则该解决方案效果很好。

您需要执行以下操作，因为描述属性不可序列化。

[DataContract]
public enum ControlSelectionType
{
    [EnumMember(Value = "Not Applicable")]
    NotApplicable = 1,
    [EnumMember(Value = "Single Select Radio Buttons")]
    SingleSelectRadioButtons = 2,
    [EnumMember(Value = "Completely Different Display Text")]
    SingleSelectDropDownList = 3,
}

public static string GetDescriptionFromEnumValue(Enum value)
{
        EnumMemberAttribute attribute = value.GetType()
            .GetField(value.ToString())
            .GetCustomAttributes(typeof(EnumMemberAttribute), false)
            .SingleOrDefault() as EnumMemberAttribute;
        return attribute == null ? value.ToString() : attribute.Value;
}

Answer 4

应该很简单，和你之前的方法相反；

public static int GetEnumFromDescription(string description, Type enumType)
{
    foreach (var field in enumType.GetFields())
    {
        DescriptionAttribute attribute
            = Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute))as DescriptionAttribute;
        if(attribute == null)
            continue;
        if(attribute.Description == description)
        {
            return (int) field.GetValue(null);
        }
    }
    return 0;
}

用法：

Console.WriteLine((Animal)GetEnumFromDescription("Giant Panda",typeof(Animal)));

Answer 5

您不能扩展 Enum，因为它是一个静态类。您只能扩展一个类型的实例。考虑到这一点，您将不得不自己创建一个静态方法来执行此操作；与您现有的方法 GetDescription 结合使用时，以下内容应该可以工作：

public static class EnumHelper
{
    public static T GetEnumFromString<T>(string value)
    {
        if (Enum.IsDefined(typeof(T), value))
        {
            return (T)Enum.Parse(typeof(T), value, true);
        }
        else
        {
            string[] enumNames = Enum.GetNames(typeof(T));
            foreach (string enumName in enumNames)
            {  
                object e = Enum.Parse(typeof(T), enumName);
                if (value == GetDescription((Enum)e))
                {
                    return (T)e;
                }
            }
        }
        throw new ArgumentException("The value '" + value 
            + "' does not match a valid enum name or description.");
    }
}

它的用法是这样的：

Animal giantPanda = EnumHelper.GetEnumFromString<Animal>("Giant Panda");

Answer 6

您需要遍历Animal中的所有枚举值，并返回与您需要的描述相匹配的值。