MVC 3 Dropdownlist用于搜索的链接模态查看列表在回发中始终为空

Question

我有一个带有过滤器的搜索表单。 1过滤器是范围，这是一个数字下拉。我有一个视图使用一个查看范围（我的数据库表）ienumerable视图和控制器我填充这个和所有的作品，因为它应该...直到表单显示，用户试图再次过滤，在这种情况下，我的模型视图ienumerable现在为null。为什么它会失去价值。我是否需要每次用户重新设置一次新的过滤器......如果可以，不需要重复调​​用数据库，因为下拉列表中的值不会改变。

模式的看法

public class SearchResultsViewModel 
{ 
    public int? Page { get; set; } 
    public penguin.Models.Job Job { get; set; } 
    public IPagedList<Models.Job> SearchResults { get; set; } 
    public string SearchButton { get; set; } 

    [Display(Name = "keywords")] 
    public string keywords { get; set; } 
    [Display(Name = "location")] 
    public string location { get; set; } 
    public int RangeID { get; set; } 
    public IEnumerable<Models.SearchRange> Range { get; set; } 

} 

控制器

const int RecordsPerPage = 25; 
    public ActionResult Jobs(ViewModels.SearchResultsViewModel model) 
    { 

     // do something with the search value      
     if (!string.IsNullOrEmpty(model.SearchButton) || model.Page.HasValue) 
     { 

      var entities = new Models.DBDataContext(); 
      var results = entities.Jobs; 

      var pageIndex = model.Page ?? 1; 
      model.SearchResults = results.ToPagedList(pageIndex, 25); 

      //Range = ViewData["Range"] as IEnumerable<Models.SearchRange>; 
     } 
     else { 
      var Data = Helpers.ModelHelpers.GetDataContext(); 
      var ranges = (from r in Data.SearchRanges select r); 
      model.Range = ranges; 
      //Range = ranges; 

     } 
     //ViewData["Range"] = Range; 
     //model.Range = Range; 
     return View(model); 


    } 

查看

@using PagedList.Mvc; 
@model ViewModels.SearchResultsViewModel   
@{ 
    ViewBag.Title = "Jobs"; 
} 
@section search { 
@using (Html.BeginForm("Jobs", "Search", FormMethod.Post, new { id = "searchForm" })) 
{ 
    <fieldset> 
     @Html.LabelFor(m => m.keywords) 
     @Html.TextBoxFor(m => m.keywords) 
     @Html.LabelFor(m => m.location) 
     @Html.TextBoxFor(m => m.location) 

     @Html.DropDownListFor(m => m.RangeID, new SelectList(Model.Range, "ID", "Range", 5)) 
     <input name="SearchButton" type="submit" value="Search" /> 
    </fieldset> 

    } 
} 
<h2> 
Jobs</h2> 
<div id="resultContainer"> 
my paged results set will go in here with a link to view job details. I then want 
it to come back here and not lose anything 
@* html.Action("Results", "Search")*@ 
@if (Model.SearchResults != null && Model.SearchResults.Count > 0) 
{ 
    foreach (var result in Model.SearchResults) 
    { 
    <hr /> 
    <table width="100%"> 
     <tr> 
      <td valign="top"> 
       <div style="font-weight: bold; font-size: large;"> 
        @Html.Raw(@result.Title.Truncate(50))</div> 
       @Html.Raw(@result.summary.Truncate(50))<br /> 
       </td> 
        </tr> 
    </table> 

    } 

    <hr />   

    @Html.PagedListPager(Model.SearchResults, page => Url.Action("Jobs", new RouteValueDictionary() { 
       { "Page", page }, 
       { "Job", Model.Job } 
       }), PagedListRenderOptions.DefaultPlusFirstAndLast)} 
    </div> 

Answer 1

如果下拉列表中的值不会改变（曾经），那么你可能应该缓存它们服务器端，每次只重用这些值。您将需要每次向模型提供值，因为数据不会在连续请求之间持续存在。 MVC中没有视图状态来保留这些值。实际上，这是一件好事。

private static IEnumerable SearchRange { get; set; } 

static SearchController() 
{ 
    SearchRange = new MyDataContext().SearchRanges.AsEnumerable(); 
} 

public ActionResult Jobs(ViewModels.SearchResultsViewModel model) 
{ 
    model.Range = SearchRange; 
    ... 
}