Question

I have an Html Helper that converts an Enum into a SelectList like so:

public static HtmlString EnumSelectListFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, TProperty>> forExpression,
    object htmlAttributes,
    bool blankFirstLine) where TModel : class where TProperty : struct
{
    //MS, it its infinite wisdom, does not allow enums as a generic constraint, so we have to check here.
    if (!typeof(TProperty).IsEnum) throw new ArgumentException("This helper method requires the specified model property to be an enum type.");

    //initialize values
    var metaData = ModelMetadata.FromLambdaExpression(forExpression, htmlHelper.ViewData);
    var propertyName = metaData.PropertyName;
    var propertyValue = htmlHelper.ViewData.Eval(propertyName).ToStringOrEmpty();

    //build the select tag
    var returnText = string.Format("<select id=\"{0}\" name=\"{0}\"", HttpUtility.HtmlEncode(propertyName));
    if (htmlAttributes != null)
    {
        foreach (var kvp in htmlAttributes.GetType().GetProperties()
            .ToDictionary(p => p.Name, p => p.GetValue(htmlAttributes, null)))
        {
            returnText += string.Format(" {0}=\"{1}\"", HttpUtility.HtmlEncode(kvp.Key),
                HttpUtility.HtmlEncode(kvp.Value.ToStringOrEmpty()));
        }
    }
    returnText += ">\n";

    if (blankFirstLine)
    {
        returnText += "<option value=\"\"></option>";
    }

    //build the options tags
    foreach (var enumName in Enum.GetNames(typeof(TProperty)))
    {
        var idValue = ((int)Enum.Parse(typeof(TProperty), enumName, true)).ToString();
        var displayValue = enumName;
        var titleValue = string.Empty;
        returnText += string.Format("<option value=\"{0}\" title=\"{1}\"",
            HttpUtility.HtmlEncode(idValue), HttpUtility.HtmlEncode(titleValue));
        if (enumName == propertyValue)
        {
            returnText += " selected=\"selected\"";
        }
        returnText += string.Format(">{0}</option>\n", HttpUtility.HtmlEncode(displayValue));
    }

    //close the select tag
    returnText += "</select>";
    return new HtmlString(returnText);
}

Problem I have is, the Enums can’t have spaces in their names, so you can get some ugly select lists if you have something other than one-word enum values, like so:

public enum EmployeeTypes
{
    FullTime = 1,
    PartTime,
    Vendor,
    Contractor
}

Now, I had the bright idea, “I know! I’ll use DataAnnotations for this!”… so I made my enum look like this:

public enum EmployeeTypes
{
    [Display(Name = "Full Time")]
    FullTime = 1,
    [Display(Name = "Part Time")]
    PartTime,
    [Display(Name = "Vendor")]
    Vendor,
    [Display(Name = "Contractor")]
    Contractor
}

… but now I’m scratching my head how to access those attributes in my helper class. Can someone get me going on this?

Answer 1

You could read the DisplayAttribute from the enum field using reflection inside the loop:

foreach (var enumName in Enum.GetNames(typeof(TProperty)))
{
    var idValue = ((int)Enum.Parse(typeof(TProperty), enumName, true)).ToString();
    var displayValue = enumName;

    // get the corresponding enum field using reflection
    var field = typeof(TProperty).GetField(enumName);
    var display = ((DisplayAttribute[])field.GetCustomAttributes(typeof(DisplayAttribute), false)).FirstOrDefault();
    if (display != null)
    {
        // The enum field is decorated with the DisplayAttribute =>
        // use its value
        displayValue = display.Name;
    }

    var titleValue = string.Empty;
    returnText += string.Format("<option value=\"{0}\" title=\"{1}\"",
        HttpUtility.HtmlEncode(idValue), HttpUtility.HtmlEncode(titleValue));
    if (enumName == propertyValue)
    {
        returnText += " selected=\"selected\"";
    }
    returnText += string.Format(">{0}</option>\n", HttpUtility.HtmlEncode(displayValue));
}