How to get an IEnumerable<string> of enum values attributes?

Question

I have a StringValue attribute for enums values, so I could attach a description to each value:

public class StringValueAttribute : Attribute
{
    public string Value { get; private set; }

    public StringValueAttribute(string value)
    {
        Value = value;
    }
}

And that is how I use it:

enum Group
{
    [StringValue("Computer Science")]
    ComputerScience,

    [StringValue("Software Engineering")]
    SoftwareEngineering,

    // ... additional values follow.
}

I have a method that retrieves the StringValue given the enum value:

public static string GetStringValue(Enum value)
{
    Type type = value.GetType();
    FieldInfo fieldInfo = type.GetField(type.ToString());
    StringValueAttribute[] attributes = fieldInfo.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];

    string stringValue = null;
    if (attributes.Length > 0)
    {
        stringValue = attributes[0].Value;
    }

    return stringValue;
}

I want to have another method that gets an enum (the enum itself, not a value) and retrieves an IEnumerable using the GetStringValue method. I am not sure how to accomplish that. How could a method like this look like?

---

Edit: this question is not a duplicate of How to get C# Enum description from value? . I know how to get an enum attribute value, and I actually have a method in the question that does exactly that. My question is how to enumerate all the attributes in an enum.

Answer 1

The most straightforward way to do this is with a generic, though you could always pass in an instance of your specific Enum , get its type, then return the StringValue values for all its values:

public static class EnumExtensions
{
    public static IEnumerable<string> GetStringValues<TEnum>() where TEnum : struct, IConvertible, IComparable, IFormattable
    {
        return Enum.GetValues(typeof(TEnum))
            .Cast<Enum>()
            .Select(e => e.GetStringValue())
            .ToList();
    }

    public static IEnumerable<string> GetStringValuesOfType(Enum value)
    {
        return Enum.GetValues(value.GetType())
            .Cast<Enum>()
            .Select(e => e.GetStringValue())
            .ToList();
    }

    public static string GetStringValue(this Enum value)
    {
        Type type = value.GetType();
        FieldInfo fieldInfo = type.GetField(value.ToString());
        StringValueAttribute[] attributes = fieldInfo.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];

        string stringValue = null;
        if (attributes.Length > 0)
        {
            stringValue = attributes[0].Value;
        }

        return stringValue;
    }
}

Notes:

• There is no where TEnum : Enum constraint in c#. Restricting TEnum to be struct, IConvertible, IComparable, IFormattable is mostly sufficient.

• That being said, there is a cunning trick to apply an enum constraint which is shown in this answer to Enum type constraints in C# by SLaks . (I didn't use it in this answer though since it's really very cunning.)

• As noted in @EdPlunkett's comment you need to pass value.ToString() to type.GetField() since you're getting the field corresponding to that specific incoming enum value.

Sample fiddle

Answer 2

This should work:

static void Main(string[] args)
{
    foreach (var item in GetStringNames<Group>())
    {
        Console.WriteLine(item);
    }
}
public static string GetStringValue(Enum value)
{
    Type type = value.GetType();
    FieldInfo fieldInfo = type.GetField(value.ToString());
    StringValueAttribute[] attributes = fieldInfo.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];

    string stringValue = null;
    if (attributes.Length > 0)
    {
        stringValue = attributes[0].Value;
    }

    return stringValue;
}

public static IEnumerable<string> GetStringNames<T>()
{
    var type = typeof(T);

    if (type.IsEnum == false)
    {
        throw new ArgumentException("T must be an Enum type");
    }

    var values = type.GetEnumValues();

    foreach (var item in values)
    {
        yield return GetStringValue((Enum)item);
    }
}