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C# - Extension method for filtering enum value in razor forms

Veröffentlicht von am 16.11.2015
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The extension method EnumDropDownListFor has an extra parameter to filter enum-values in a dropdownlist in an asp.net razor form.

Example:

<div>
@Html.EnumDropDownListFor(
model => model.Category,
(category => (category != Category.Books)),
new { @class = "form-control" })
</div>
namespace HtmlHelper.Extensions
{
    using System;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Web.Mvc;
    using System.Web.Mvc.Html;

    public static class SelectExtension
    {
        public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper,
        Expression<Func<TModel, TEnum>> expression, Func<TEnum, bool> filter, object htmlAttributes) where TEnum : IConvertible
        {
            if (expression == null)
            {
                throw new ArgumentNullException("expression");
            }

            if (!typeof(TEnum).IsEnum)
            {
                throw new ArgumentException("TEnum");
            }

            var selectList = Enum.GetValues(typeof(TEnum))
                    .Cast<TEnum>()
                    .Where(e => filter(e))
                    .Select(e => new SelectListItem
                    {
                        Value = e.ToUInt64(null).ToString(),
                        Text = e.ToString(),
                    });

            return htmlHelper.DropDownListFor(expression, selectList, htmlAttributes);
        }
    }
}

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