Getting Description Attribute of a Generic Enum

Question

I'm having some hard time with trying to be generic with enums. I've read that it's not that simple, and I can't seem to find a solution.

I'm trying to create a generic function, that for an enum type would return the description for each enum value. I want to keep it generic and not to duplicate this method for each enum type...

Here's what I have so far:

public static KeyValuePair<string, List<KeyValueDataItem>> ConvertEnumWithDescription<T>()
    where T : struct, IConvertible
{
    if (!typeof(T).IsEnum)
    {
        throw new Exception("Type given T must be an Enum");
    }

    var enumType = typeof(T).ToString().Split('.').Last();

    var itemsList = Enum.GetValues(typeof(T))
            .Cast<T>()
            .Select(x => new KeyValueDataItem
            {
                Key = Convert.ToInt32(x),
                Value = GetEnumDescription(Convert.ToInt32(x))
            })
            .ToList();

    var res = new KeyValuePair<string, List<KeyValueDataItem>>(enumType, itemsList);

    return res;
}

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

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

    if (attributes.Length > 0)
        return attributes[0].Description;

    return value.ToString();
}

The issue I'm currently having is that:

cannot convert from 'int' to 'System.Enum'

When I'm trying to call the function GetEnumDescription. If I convert it to T:

Value = GetEnumDescription((T)(object)Convert.ToInt32(x));

This is the error I'm getting:

cannot convert from 'T' to 'System.Enum'

Kulight · Accepted Answer · 2016-04-12 13:17:24Z

Here, try this:

public static KeyValuePair<string, List<KeyValueDataItem>> ConvertEnumWithDescription<T>() where T : struct, IConvertible
    {
        if (!typeof(T).IsEnum)
        {
            throw new Exception("Type given T must be an Enum");
        }

        var enumType = typeof(T).ToString().Split('.').Last();
        var itemsList = Enum.GetValues(typeof(T))
              .Cast<T>()
               .Select(x => new KeyValueDataItem
               {
                   Key = Convert.ToInt32(x),
                   Value = GetEnumDescription<T>(x.ToString())
               })
               .ToList();

        var res = new KeyValuePair<string, List<KeyValueDataItem>>(
            enumType, itemsList);
        return res;

    }

    public static string GetEnumDescription<T>(string value)
    {
        Type type = typeof(T);
        var name = Enum.GetNames(type).Where(f => f.Equals(value, StringComparison.CurrentCultureIgnoreCase)).Select(d => d).FirstOrDefault();

        if (name == null)
        {
            return string.Empty;
        }
        var field = type.GetField(name);
        var customAttribute = field.GetCustomAttributes(typeof(DescriptionAttribute), false);
        return customAttribute.Length > 0 ? ((DescriptionAttribute)customAttribute[0]).Description : name;
}

Based on: http://www.extensionmethod.net/csharp/enum/getenumdescription

Moti Azu · Accepted Answer · 2016-04-12 13:18:22Z

I took the liberty of modifying some parts of the code, like changing the return types to more C# standard API return values.

You can watch it run here.

public static EnumDescription ConvertEnumWithDescription<T>() where T : struct, IConvertible
{
    if (!typeof(T).IsEnum)
    {
        throw new ArgumentException("Type given T must be an Enum");
    }

    var enumType = typeof(T).Name;
    var valueDescriptions = Enum.GetValues(typeof (T))
        .Cast<Enum>()
        .ToDictionary(Convert.ToInt32, GetEnumDescription);

    return new EnumDescription
    {
        Type = enumType,
        ValueDescriptions = valueDescriptions
    };

}

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

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

    if (attributes.Length > 0)
        return attributes[0].Description;
    return value.ToString();
}

public class EnumDescription
{
    public string Type { get; set; }
    public IDictionary<int, string> ValueDescriptions { get; set; }
}

momar · Accepted Answer · 2016-04-12 13:14:50Z

Modified your code slightly to pass in a Type to the description method and pass the parameter as a string value. This then gets converted back to the appropriate enum type and checked for the description.

public static KeyValuePair<string, List<KeyValueDataItem>> ConvertEnumWithDescription<T>() where T : struct, IConvertible
{
        if (!typeof(T).IsEnum)
        {
            throw new Exception("Type given T must be an Enum");
        }

        var enumType = typeof(T).ToString().Split('.').Last();
        var type = typeof(T);

        var itemsList = Enum.GetValues(typeof(T))
                .Cast<T>()
                .Select(x => new KeyValueDataItem
                {
                    Key = Convert.ToInt32(x),
                    Value = GetEnumDescription<T>(Enum.GetName(typeof(T), x))
                })
                .ToList();

        var res = new KeyValuePair<string, List<KeyValueDataItem>>(
            enumType, itemsList);
        return res;

}       

public static string GetEnumDescription<T>(string enumValue)
{
    var value = Enum.Parse(typeof(T), enumValue);
    FieldInfo fi = value.GetType().GetField(value.ToString());

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

    if (attributes.Length > 0)
        return attributes[0].Description;
    return value.ToString();
}

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