HtmlHelperExtensions.cs

using System;
using System.Linq;
using System.Web.Mvc;

namespace SampleApp.Helpers
{
    public static class HtmlHelperExtensions
    {
        public static SelectListItem[] Months(this HtmlHelper htmlHelper, DateTime from, DateTime to, DateTime selected)
        {
            return Enumerable.Range(0, (to.Year - from.Year) * 12 + (to.Month - from.Month + 1))
                         .Select(m => new DateTime(from.Year, from.Month, 1).AddMonths(m))
                         .OrderByDescending(x => x)
                         .Select(x =>
                          {
                              var listItem = new SelectListItem
                              {
                                  Text = x.ToString("yyyy年MM月"),
                                  Value = x.ToString("yyyy-MM-dd")
                              };

                              if (x == selected)
                              {
                                  listItem.Selected = true;
                              }

                              return listItem;
                          }).ToArray();
        }

        public static SelectListItem[] Ints(this HtmlHelper htmlHelper, int from, int to, int selected)
        {
            if (from >= to)
            {
                return new SelectListItem[0];
            }

            return Enumerable.Range(from, to - from)
                         .Select(x =>
                         {
                             var listItem = new SelectListItem
                             {
                                 Text = x.ToString(),
                                 Value = x.ToString()
                             };

                             if (x == selected)
                             {
                                 listItem.Selected = true;
                             }

                             return listItem;
                         }).ToArray();
        }
    }
}