Question

 static void Main(string[] args)
    {
        List<string> tests = new List<string>() { "TypeTester.NonExist", "TypeTester.Thing", "TypeTester.Fruit", "TypeTester.Color" };
        PrintEnums();
        foreach (var item in tests)
        {
            try
            {
                ConvertFromTypeName(item);
            }
            catch (TypeLoadException)
            {
                Console.WriteLine("Could not load {0}", item);
            }
            catch (ArgumentException e)
            {
                Console.WriteLine(e.Message);
            }    
        }
        Console.ReadLine();
    }

    static void PrintEnums()
    {
        Console.WriteLine("Printing Fruit");
        foreach (Fruit thing in Enum.GetValues(typeof(Fruit)))
        {
            Console.WriteLine("Value: {0}, Description: {1}", (int)thing, thing.GetDescription());
        }
        Console.WriteLine("Printing Color");
        foreach (Color thing in Enum.GetValues(typeof(Color)))
        {
            Console.WriteLine("Value: {0}, Description: {1}", (int)thing, thing.GetDescription());
        }
    }

    static void ConvertFromTypeName(string typeName)
    {
        Type type = Type.GetType(typeName, true);
        if (!type.IsEnum)
            throw new ArgumentException(typeName + " is not an enum.");

        Console.WriteLine("UnderlingType: {0}", type.UnderlyingSystemType);
        string description = string.Empty;
        foreach ( var thing in Enum.GetValues((type.UnderlyingSystemType)))
            {
//This will not compile                
//Console.WriteLine("Value: {0}, Description: {1}", (int)thing, thing.GetDescription());
                Console.WriteLine("Value: {0}, Description: {1}", (int)thing, thing.ToString());
        }
    }
}

public class Thing
{
    public int Id { get; set; }
    public string MyName { get; set; }
}

public enum Fruit
{
    [System.ComponentModel.DescriptionAttribute("I am an apple")]
    Apple = 8,
    [System.ComponentModel.DescriptionAttribute("I am an Banana")]
    Banana,
    [System.ComponentModel.DescriptionAttribute("I am an Grape")]
    Grape,
    [System.ComponentModel.DescriptionAttribute("I am an Kiwi")]
    Kiwi,
    [System.ComponentModel.DescriptionAttribute("I am an Orange")]
    Orange
}

public enum Color
{
    [System.ComponentModel.DescriptionAttribute("I am the color Red")]
    Red = 56,
    [System.ComponentModel.DescriptionAttribute("I am the color Green")]
    Green,
    [System.ComponentModel.DescriptionAttribute("I am the color Blue")]
    Blue,
    [System.ComponentModel.DescriptionAttribute("I am the color Black")]
    Black,
    [System.ComponentModel.DescriptionAttribute("I am the color White")]
    White
}

public static class Helper
{
    public static string GetDescription(this Enum value)
    {
        System.Reflection.FieldInfo field = value.GetType().GetField(value.ToString());
        System.ComponentModel.DescriptionAttribute attribute = Attribute.GetCustomAttribute(field, typeof(System.ComponentModel.DescriptionAttribute)) as System.ComponentModel.DescriptionAttribute;
        return attribute == null ? value.ToString() : attribute.Description;
    }
}

为什么在ConvertFromTypeName中如果底层类型是Fruit或Color我不能调用GetDescription扩展方法？它似乎无法从var中推断出来。我希望这个工作就像PrintEnums，GetDescription扩展。

Printing Fruit
Value: 8, Description: I am an apple
Value: 9, Description: I am an Banana
Value: 10, Description: I am an Grape
Value: 11, Description: I am an Kiwi
Value: 12, Description: I am an Orange
Printing Color
Value: 56, Description: I am the color Red
Value: 57, Description: I am the color Green
Value: 58, Description: I am the color Blue
Value: 59, Description: I am the color Black
Value: 60, Description: I am the color White
Could not load TypeTester.NonExist
TypeTester.Thing is not an enum.
UnderlingType: TypeTester.Fruit
Value: 8, Description: Apple
Value: 9, Description: Banana
Value: 10, Description: Grape
Value: 11, Description: Kiwi
Value: 12, Description: Orange
UnderlingType: TypeTester.Color
Value: 56, Description: Red
Value: 57, Description: Green
Value: 58, Description: Blue
Value: 59, Description: Black
Value: 60, Description: White

Answer 1

知道了。在ConvertFrom TypeName方法的foreach中，我改变了

Console.WriteLine("Value: {0}, Description: {1}", (int)thing, thing.ToString());

到

Console.WriteLine("Value: {0}, Description: {1}", (int)thing, ((Enum)thing).GetDescription());

看起来我需要做的就是向Enum投射东西以获得@扩展方法

Answer 2

您将枚举类型与其基础类型混淆。看看这段代码：

Type type = Type.GetType(typeName, true);
if (!type.IsEnum)
    throw new ArgumentException(typeName + " is not an enum.");

Console.WriteLine("UnderlingType: {0}", type.UnderlyingSystemType);
string description = string.Empty;
foreach ( var thing in Enum.GetValues((type.UnderlyingSystemType)))
{
    ...
}

这里，type是枚举类型 - 那么为什么要获取基础类型？在你给出的两种情况下，这都是int。不是枚举类型，因此Enum.GetValues显然会失败。

你只想：

foreach (var thing in Enum.GetValues(type))

从类型枚举并调用扩展方法

2 个答案: