.NET Core的枚举反射

Question

我正在尝试使DisplayAttribute属性适用于enum，因此我可以列出可用的值（向RESTful API公开）。

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，我制作了一些辅助方法，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;
    }

用法是：

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

但是，GetAttribute<TAttribute>当我尝试获取要查找的属性时，似乎正在发生这种情况：

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

...结果值是一个空的枚举，因此返回空值。从我读过的所有内容来看，这应该可以正常工作，并且我应该找回关联的值DisplayAttribute……但是我找回一个空值。

我究竟做错了什么？

Answer 1

问题是您正在寻找ProposalTypes类型的属性，而不是类型的值。有关 获取枚举值的属性的信息，请参见此问题。

更确切地说，GetAttribute您需要获取代表您的特定值的成员并对其进行调用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;
}