asp.net MVC 3 pre-选择Html.DropDownListFor的书呆子晚餐不工作 [英] asp.net mvc 3 pre-select Html.DropDownListFor not working in nerd dinner

问题描述

学习一下下拉列表中，我试着给的NerdDinner添加RSVP创建页面中的斯科特谷的一个Html.DropDownListFor博客列出可用晚餐。

Learning about dropdown lists, Im trying to add a RSVP create page for nerddinner as in Scott Gu's blog with a Html.DropDownListFor listing available dinners.

我可以得到填充的下拉列表中，但我不能让下拉至pre选择数值（样本晚餐2）我想要的。 IM使用initilizer种子的分贝数晚宴的对象。该数据库是使用EF'code第一种方法'SQL CE 4。对不起，我知道这是一个V常见的问题和仇恨来问，但说实话已经花了相当长的一段时间这一点，但不能得到它的工作：

I can get the dropdown list populated but I cannot get the dropdown to pre select the value ("Sample Dinner 2") I want. Im using an initilizer to seed a few dinner objects in the db. The database is sql ce 4 using a EF 'code first approach'. Sorry I know this is a v common problem and hate to ask, but honestly have spent quite some time on this but cant get it to work:

视图模型

public class RSVPViewModel
{
    public SelectList DinnersList { get; set; }
    public RSVP Rsvp { get; set; }
    public string SelectedItem { get; set; }
}

控制器

    //
    //GET: /RSVP/Create

    public ActionResult Create()
    {
        RSVP rsvp = new RSVP();
        string selected = "Sample Dinner 2";
        var typeList = new SelectList(dbc.Dinners.ToList(), "DinnerID", "Title", selected);

        var viewModel = new RSVPViewModel { DinnersList = typeList, Rsvp = rsvp, SelectedItem = selected };

        return View("Create", viewModel);
    }

查看

@Html.DropDownListFor(model => model.Rsvp.DinnerID, Model.DinnersList)

HTML结果

<select data-val="true" data-val-number="The field DinnerID must be a number." data-val-required="The DinnerID field is required." id="Rsvp_DinnerID" name="Rsvp.DinnerID">
     <option value="1">Sample Dinner 1</option>
     <option value="2">Sample Dinner 2</option>
</select>

那么是不是preselecting与价值样品2晚餐页面加载时的DropDownList。列表显示确定并设置正确的DinnerID当我做出选择并点击提交。

So is not preselecting the dropdownlist with the value "Sample Dinner 2" when the page loads. The list displays ok and sets the correct DinnerID when I make a selection and click Submit.

尝试，这也：

@Html.DropDownListFor(x => x.SelectedItem, Model.DinnersList)

但犯规设置或绑定到Rsvp.DinnerID。

but doesnt set or bind to Rsvp.DinnerID.

从列表中，但犯规绑定（或设置Rsvp.DinnerID）这preselects

This preselects from the list but doesnt bind (or set Rsvp.DinnerID)

@Html.DropDownList("DinnersList")

我想保持它MVC3所以想用视图模型方法（无的ViewData）和preferably使用Html.DropDownListFor强类型来实现（不Html.DropDownList）.Viewbag似乎没有必要为这种情况。

I want to keep it mvc3 so want to implement with strong type using ViewModel approach (no ViewData) and preferably using Html.DropDownListFor (not Html.DropDownList).Viewbag seems unnecessary for this case.

谢谢！

EDIT1

想我应该使用selectListItems的选择列表我尝试这样冗长的方法：

Thinking I should be using a selectList of selectListItems I tried this verbose approach :

RSVP rsvp = new RSVP();
string selected = "2";
List<SelectListItem> dinners = new List<SelectListItem>();

foreach (Dinner dinner in dbc.Dinners.ToList())
{
    SelectListItem slDinner = new SelectListItem();
    slDinner.Value = dinner.DinnerID.ToString();
    slDinner.Text = dinner.Title;
    slDinner.Selected = (slDinner.Value == selected);
    dinners.Add(slDinner);
 }

 var dinnersList = new SelectList(dinners, "Value", "Text", selected);
 var viewModel = new RSVPViewModel { DinnersList = dinnersList, Rsvp = rsvp, SelectedItem = selected };

但仍然没有工作。我应该让使用的视图模型SelectedItem属性的：@ Html.DropDownListFor ..不知何故？是这样的：

However still no work. Should I be making use of the ViewModel SelectedItem property in: @Html.DropDownListFor.. somehow? Something like :

@Html.DropDownListFor(x => x.SelectedItem, Model.DinnersList)

但如何我得到一个选择的值来设置Rsvp.DinnerID。我觉得这就是所谓的绑定。

but how to I get a selected value to set Rsvp.DinnerID. I think thats called binding.

推荐答案

这里和阅读后< A HREF =htt​​p://forums.asp.net/p/1602742/4083713.aspx>这里，我终于明白如何HtmlDropDownlistFor自动在下拉列表中选择正确的项目基于模型 - 选择在RSVP一个dinnerID（外键dinner.dinnerID）将导致Dinner.DinnerIDs以pre含有下拉列表中选择该值。没有必要的没有的我觉得在了selectedValue选择列表或视图模型。

After reading here and here, I finally understand how HtmlDropDownlistFor automatically selects the correct item in the dropdown based on your model - selecting a dinnerID in RSVP (foreign key to dinner.dinnerID) will cause the dropdown containing list of Dinner.DinnerIDs to pre select that value. No need yet I think for selectedValue in the SelectList or ViewModel.

解决方案：

    //
    //GET: /RSVP/Create

    public ActionResult Create()
    {
        //automatically preselects matching DinnerID in the Dinner dropdownlist            
        var rsvp = new RSVP {DinnerID = 2 };

        var typeList = new SelectList(dbc.Dinners.ToList(), "DinnerID", "Title");
        var viewModel = new RSVPViewModel { DinnersList = typeList, Rsvp = rsvp};

        return View("Create", viewModel);
    }

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