Creating generic extension method for getting list of values' Display Name attribute strings

Question

I am working on an AngularJS/Asp.Net MVC project and I have several Enums that have [Display(Name = "Value")] attributes on their values. I have an extension method that can extract the display name from these that works well enough:

public static string GetDisplayName(this Enum value)
{
    Type enumType = value.GetType();
    var enumValue = Enum.GetName(enumType, value);
    MemberInfo member = enumType.GetMember(enumValue)[0];

    var attrs = member.GetCustomAttributes(typeof(DisplayAttribute), false);
    var outString = ((DisplayAttribute)attrs[0]).Name;

    if (((DisplayAttribute)attrs[0]).ResourceType != null)
    {
        outString = ((DisplayAttribute)attrs[0]).GetName();
    }

    return outString;
}

Converting these Enums to Lists of the display name string values is easy enough:

//TODO: there *has* to be a way to do this with a generic or extension method
ViewBag.CurrencyTypes = Enum.GetValues(typeof(ProjectName.Web.Models.Common.CurrencyType)).Cast<ProjectName.Web.Models.Common.CurrencyType>().Select(v => v.GetDisplayName()).ToList();
ViewBag.PaymentTypes = Enum.GetValues(typeof(ProjectName.Web.Models.Common.PaymentType)).Cast<ProjectName.Web.Models.Common.PaymentType>().Select(v => v.GetDisplayName()).ToList();
ViewBag.OrgTypes = Enum.GetValues(typeof(ProjectName.Web.Models.Common.OrganizationType)).Cast<ProjectName.Web.Models.Common.OrganizationType>().Select(v => v.GetDisplayName()).ToList();
ViewBag.States = Enum.GetValues(typeof(ProjectName.Web.Models.Common.State)).Cast<ProjectName.Web.Models.Common.State>().Select(v => v.GetDisplayName()).ToList();

What I'm trying to figure out is, how do I create a common extension method that can create these lists? I tried using generics but adding where T : Enum throws an error.

Update: based on the type constriction of where T : struct, IConvertible from @Marcel's link, and the function @empi posted I have this static helper function:

public static List<string> GetDisplayList<T>() where T : struct, IConvertible
{
    if (!typeof(T).IsEnum)
    {
        throw new ArgumentException("T must be an enumerated type");
    }
    return Enum.GetValues(typeof(T)).Cast<Enum>().Select(v => v.GetDisplayName()).ToList();
}

Is there a way to make this an extension method?

Maybe this can get you started: http://stackoverflow.com/questions/79126/create-generic-method-constraining-t-to-an-enum — Marcel N., Aug 19 '14 at 19:50
Extension methods only work with instances, not on types. I mean, how would you even call an extension method on an enum type? I think that generic method is as good as it gets. Also relevant: http://stackoverflow.com/questions/2422113/extension-method-on-enumeration-not-instance-of-enumeration — Marcel N., Aug 19 '14 at 20:20

score 2 · Accepted Answer · edited May 23 '17 at 12:07

2

Do you really need an extension method? A simple static method solves this problem:

public static List<string> CreateList<T>()
{
    return Enum.GetValues(typeof(T)).Cast<Enum>().Select(v => v.GetDisplayName()).ToList();
}

And when it comes to generic constraints you should look at Create Generic method constraining T to an Enum as stated in comments.

edited May 23 '17 at 12:07

Community

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answered Aug 19 '14 at 20:00

empi

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I don't, and I tried something similar but I was trying to `Cast` instead of `Cast` this may work, I'll try it… – travis Aug 19 '14 at 20:09

Creating generic extension method for getting list of values' Display Name attribute strings

1 Answers1