using System;

using System.ComponentModel.DataAnnotations;

public enum BillingCycle

{

    [Display(Name="This is monthly")]

    Monthly = -1,

    [Display(Name="This is monthly in advance")]

    MonthlyInAdvance = 1,

    Quarterly = 3,

    QuarterlyInArrears = -3,

    SixMonthly = 6,

    SixMonthlyInArrears = -6,

    Annually = 12,

    AnnuallyInArrears = -12,

    NonStandardCustom

}

​

public class Program

{

    public static void Main()

    {       

        Console.WriteLine(((BillingCycle)(-1)).GetDisplayName());

        Console.WriteLine(((BillingCycle)1).GetDisplayName());

        Console.WriteLine(((BillingCycle)6).GetDisplayName());

        Console.WriteLine(((BillingCycle)100).GetDisplayName());

    }

}

​

public static class EnumExtensions

{

    /// <summary>

    /// <para>Retrieves the Display Name of an enum value</para>

    /// <para>Throws <see cref="ArgumentException"/> if value passed in is not an enum of member can't be found</para>

    /// <para>Returns the Display Name set on the <see cref="DisplayAttribute"/> or the member name if attribute is not defined or Name is empty</para>

    /// </summary>

    public static string GetDisplayName(this Enum value)

    {

        var type = value.GetType();

        if (!type.IsEnum)

        {

            throw new ArgumentException($"Type '{type}' is not Enum");

        }

​

        var members = type.GetMember(value.ToString());

        if (members.Length == 0)

        {

            throw new ArgumentException($"Member '{value}' not found in type '{type.Name}'");

        }

​

        var member = members[0];

        var attributes = member.GetCustomAttributes(typeof(DisplayAttribute), false);

​

        if (attributes.Length == 0 || string.IsNullOrEmpty(((DisplayAttribute)attributes[0]).GetName()))

        {

            return value.ToString();

        }

​

        var attribute = (DisplayAttribute)attributes[0];

        return attribute.GetName()!;

    }

}