c# - .NET Core 的枚举反射

Question

我正在尝试获取 DisplayAttribute为 enum 工作的属性，这样我就可以列出可用的值(以公开给 RESTful API)。

我有一个枚举如下:

/// <summary>
/// Available Proposal Types
/// </summary>
public enum ProposalTypes
{
    Undefined = 0,

    /// <summary>
    /// Propose an administrative action.
    /// </summary>
    [Display(Name = "Administrative", Description = "Propose an administrative action.")]
    Administrative,

    /// <summary>
    /// Propose some other action.
    /// </summary>
    [Display(Name = "Miscellaneous", Description = "Propose some other action.")]
    Miscellaneous
}

然后我做了一些辅助方法，如下所示:

    /// <summary>
    ///     A generic extension method that aids in reflecting
    ///     and retrieving any attribute that is applied to an `Enum`.
    /// </summary>
    public static TAttribute GetAttribute<TAttribute>(this Enum enumValue) where TAttribute : Attribute
    {
        var type = enumValue.GetType();
        var typeInfo = type.GetTypeInfo();
        var attributes = typeInfo.GetCustomAttributes<TAttribute>();
        var attribute = attributes.FirstOrDefault();
        return attribute;
    }

    /// <summary>
    /// Returns a list of possible values and their associated descriptions for a type of enumeration.
    /// </summary>
    /// <typeparam name="TEnum"></typeparam>
    /// <returns></returns>
    public static IDictionary<string, string> GetEnumPossibilities<TEnum>() where TEnum : struct
    {
        var type = typeof(TEnum);
        var info = type.GetTypeInfo();
        if (!info.IsEnum) throw new InvalidOperationException("Specified type is not an enumeration.");


        var results = new Dictionary<string, string>();
        foreach (var enumName in Enum.GetNames(type)
            .Where(x => !x.Equals("Undefined", StringComparison.CurrentCultureIgnoreCase))
            .OrderBy(x => x, StringComparer.CurrentCultureIgnoreCase))
        {
            var value = (Enum)Enum.Parse(type, enumName);
            var displayAttribute = value.GetAttribute<DisplayAttribute>();
            results[enumName] = $"{displayAttribute?.Name ?? enumName}: {displayAttribute?.Description ?? enumName}";
        }
        return results;
    }

其用法是:

var types = Reflection.GetEnumPossibilities<ProposalTypes>();

不过，似乎正在发生的事情是在 GetAttribute<TAttribute> 中。方法，当我尝试获取我正在寻找的属性时:

var attributes = typeInfo.GetCustomAttributes<TAttribute>();

...结果值是一个空枚举，因此返回一个空值。从我读到的所有内容来看，这应该可以正常工作，并且我应该取回相关的 DisplayAttribute ...但我返回一个空值。

我做错了什么？

Answer 1

问题在于您正在查找 ProposalTypes 类型的属性，而不是该类型的值。 See this Question有关获取枚举值的属性的信息。

更准确地说，在GetAttribute中，您需要获取代表您的特定值的成员，并对其调用GetCustomAttributes。您的方法将如下所示:

public static TAttribute GetAttribute<TAttribute>(this Enum enumValue) where TAttribute : Attribute
{
    var type = enumValue.GetType();
    var typeInfo = type.GetTypeInfo();
    var memberInfo = typeInfo.GetMember(enumValue.ToString());
    var attributes = memberInfo[0].GetCustomAttributes<TAttribute>();
    var attribute = attributes.FirstOrDefault();
    return attribute;
}