How to get C# Enum description from value? [duplic

问题:

Possible Duplicate:
Getting attributes of Enum’s value

I have an enum with Description attributes like this:

public enum MyEnum
{
    Name1 = 1,
    [Description(\"Here is another\")]
    HereIsAnother = 2,
    [Description(\"Last one\")]
    LastOne = 3
}

I found this bit of code for retrieving the description based on an Enum

public static string GetEnumDescription(Enum value)
{
    FieldInfo fi = value.GetType().GetField(value.ToString());

    DescriptionAttribute[] attributes =
        (DescriptionAttribute[])fi.GetCustomAttributes(
        typeof(DescriptionAttribute),
        false);

    if (attributes != null &&
        attributes.Length > 0)
        return attributes[0].Description;
    else
        return value.ToString();
}

This allows me to write code like:

var myEnumDescriptions = from MyEnum n in Enum.GetValues(typeof(MyEnum))
                         select new { ID = (int)n, Name = Enumerations.GetEnumDescription(n) };

What I want to do is if I know the enum value (e.g. 1) - how can I retrieve the description? In other words, how can I convert an integer into an \"Enum value\" to pass to my GetDescription method?

回答1:

int value = 1;
string description = Enumerations.GetEnumDescription((MyEnum)value);

The default underlying data type for an enum in C# is an int, you can just cast it.

回答2:

Update

The Unconstrained Melody library is no longer maintained; Support was dropped in favour of Enums.NET.

In Enums.NET you\'d use:

string description = ((MyEnum)value).AsString(EnumFormat.Description);

Original post

I implemented this in a generic, type-safe way in Unconstrained Melody - you\'d use:

string description = Enums.GetDescription((MyEnum)value);

This:

• Ensures (with generic type constraints) that the value really is an enum value
• Avoids the boxing in your current solution
• Caches all the descriptions to avoid using reflection on every call
• Has a bunch of other methods, including the ability to parse the value from the description

I realise the core answer was just the cast from an int to MyEnum, but if you\'re doing a lot of enum work it\'s worth thinking about using Unconstrained Melody :)

回答3:

I put the code together from the accepted answer in a generic extension method, so it could be used for all kinds of objects:

public static string DescriptionAttr<T>(this T source)
{
    FieldInfo fi = source.GetType().GetField(source.ToString());

    DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(
        typeof(DescriptionAttribute), false);

    if (attributes != null && attributes.Length > 0) return attributes[0].Description;
    else return source.ToString();
}

Using an enum like in the original post, or any other class whose property is decorated with the Description attribute, the code can be consumed like this:

string enumDesc = MyEnum.HereIsAnother.DescriptionAttr();
string classDesc = myInstance.SomeProperty.DescriptionAttr();

回答4:

To make this easier to use, I wrote a generic extension:

public static string ToDescription<TEnum>(this TEnum EnumValue) where TEnum : struct
{
    return Enumerations.GetEnumDescription((Enum)(object)((TEnum)EnumValue));
}

now I can write:

        MyEnum my = MyEnum.HereIsAnother;
        string description = my.ToDescription();
        System.Diagnostics.Debug.Print(description);

Note: replace \"Enumerations\" above with your class name

回答5:

You can\'t easily do this in a generic way: you can only convert an integer to a specific type of enum. As Nicholas has shown, this is a trivial cast if you only care about one kind of enum, but if you want to write a generic method that can handle different kinds of enums, things get a bit more complicated. You want a method along the lines of:

public static string GetEnumDescription<TEnum>(int value)
{
  return GetEnumDescription((Enum)((TEnum)value));  // error!
}

but this results in a compiler error that \"int can\'t be converted to TEnum\" (and if you work around this, that \"TEnum can\'t be converted to Enum\"). So you need to fool the compiler by inserting casts to object:

public static string GetEnumDescription<TEnum>(int value)
{
  return GetEnumDescription((Enum)(object)((TEnum)(object)value));  // ugly, but works
}

You can now call this to get a description for whatever type of enum is at hand:

GetEnumDescription<MyEnum>(1);
GetEnumDescription<YourEnum>(2);