0

我正在尝试将扩展方法添加到 Enum 类型，但下面的代码失败。编译器在线给出错误StoreType.GetAllItems如何将扩展方法添加到 Enum 类型？

namespace ConsoleApplication1
{

    public static class EnumExtensions
    {
        public static IEnumerable<T> GetAllItems<T>(this Enum value)
        {
            foreach (object item in Enum.GetValues(typeof(T)))
            {
                yield return (T)item;
            }
        }


    }

    class Program
    {

        [Flags]
        public enum StoreType
        {
            Paypal = 1,
            Plimus = 2,
            Other = 3
        };

        static void Main(string[] args)
        {            
           StoreType.GetAllItems //Fail here
        }
    }
}
4

3 回答 3

1

您会看到编译器错误，因为您无法覆盖默认的 c# enum，根据本文尝试通过将您的方法添加到自定义类来以这种方式覆盖您的枚举：

public class MyEnum
{
    public static readonly MyEnum A = new MyEnum("A");
    public static readonly MyEnum B = new MyEnum("B");
    public static readonly MyEnum C = new MyEnum("C");
    public static IEnumerable<T> GetAllItems<T>(this Enum value)
    {
        foreach (object item in Enum.GetValues(typeof(T)))
        {
            yield return (T)item;
        }
    }

    public override string ToString()
    {
        return Value;
    }

    protected MyEnum(string value)
    {
        this.Value = value;
    }

    public string Value { get; private set; }
}

public sealed class MyDerivedEnum : MyEnum
{
    public static readonly MyDerivedEnum D = new MyDerivedEnum("D");

    private MyDerivedEnum(string value)
        : base(value)
    {
    }
}

class Program
{
    static void Main(string[] args)
    {
        MyEnum blah = MyEnum.A;
        System.Console.WriteLine(blah);
        blah = MyDerivedEnum.D;
        System.Console.WriteLine(blah);
    }
}
于 2013-02-12T08:05:58.067 回答
1

您必须在一个值上调用 GetAllItems，而不是一个类型：

StoreType.Paypal.GetAllItems()

但是不让它成为扩展方法并声明它不是更好：

public static class EnumExtensions
{
    public static IEnumerable<T> GetAllItems<T>()
    {
        foreach (object item in Enum.GetValues(typeof(T)))
        {
            yield return (T)item;
        }
    }
}
static void Main(string[] args)
{            
    var allEnumItems = EnumExtensions.GetAllItems<StoreType>()
}

甚至：

Enum.GetValues(typeof (StoreType));
Enum.GetNames(typeof (StoreType));

之后您可以使用 Enum.TryParse(...) 将名称解析回枚举，我认为这是您想要的吗？

于 2013-02-12T08:02:25.480 回答
0

我会说那将是一个带有伪扩展的类。它可能看起来像这样：

用法：

List<HttpStatusCode> list = EnumUtils<HttpStatusCode>.ToList();

Dictionary<int, HttpStatusCode> map = EnumUtils<HttpStatusCode>.ToDictionary();

伪扩展类：

/// <summary>Pseudo extension class for enumerations</summary>
/// <typeparam name="TEnum">Enumeration type</typeparam>
public class EnumUtils<TEnum> where TEnum : struct, IConvertible
{
    public static List<TEnum> ToList()
    {
        var enumType = typeof(TEnum);

        return enumType.IsEnum
            ? enumType.GetEnumValues().OfType<TEnum>().ToList()
            : throw new ArgumentException($"{enumType.Name} is not enum");
    }

    public static Dictionary<int, TEnum> ToDictionary()
    {
        Type enumType = typeof(TEnum);

        return enumType.IsEnum
            ? enumType.GetEnumValues().OfType<TEnum>().ToDictionary(
                e => Convert.ToInt32(Enum.Parse(typeof(TEnum), e.ToString()) as Enum), 
                e => e)
            : throw new ArgumentException($"{enumType.Name} is not enum");
    }
}

享受！

于 2019-03-07T18:04:24.693 回答