c# 从数据库作为下拉列 删除重复的列 foreach()

  public ActionResult Index(YearCheckInfoRequest request)
        {
            //int a = -1;
            // if (request.DisasterScale == a.ToString()) { request.DisasterScale = null; };
            // if (request.MineName == a.ToString()) { request.MineName = null; };
            var result = this.YearCheckService.GetYearCheckList(request);

            YearCheckInfoRequest NewRequest = new YearCheckInfoRequest();
            Dictionary<int, String> dictionary = new Dictionary<int, string>();
            var MineNameList = this.YearCheckService.GetYearCheckList(NewRequest);
           
            int i = 0;
            List<String> mineNameList= new List<String>();
            
            foreach (YearCheckInfo yearCheck in MineNameList)
            {
                if (!mineNameList.Contains(yearCheck.MineName))
                {
                    mineNameList.Add(yearCheck.MineName);
                    dictionary.Add(i, yearCheck.MineName);
                    i++;
                }
            }
            this.ViewBag.MineName = new SelectList(dictionary, "", "value ");

            //默认查询日期
            ViewBag.CheckTimeStart = request.CheckTimeStart.ToString("yyyy-MM-dd");
            ViewBag.CheckTimeEnd = request.CheckTimeEnd.ToString("yyyy-MM-dd");

            return View(result);
        }

  <label>
                    <span>矿山名称：</span>
                    @Html.DropDownList("MineName", ViewBag.MineName as SelectList, "所有记录",new { @class = "m-wrap medium" })
                  
                </label>