Question

我是MVC3的新手我发现很难创建一个下拉列表。我已经完成了所有其他相关问题，但它们似乎都很复杂我需要创建一个下拉列表并在数据库中插入所选的值

以下是我的尝试：

//Model class:
    public int Id { get; set; }
    public SelectList hobbiename { get; set; }
    public string filelocation { get; set; }
    public string hobbydetail { get; set; }
//Inside Controller
public ActionResult Create()
    {
        var values = new[]
        { 
            new { Value = "1", Text = "Dancing" },
            new { Value = "2", Text = "Painting" }, 
            new { Value = "3", Text = "Singing" },
        };
        var model = new Hobbies
        {
           hobbiename = new SelectList(values, "Value", "Text")
        }; 
        return View();
    } 
//Inside view
 <div class="editor-label">
        @Html.LabelFor(model => model.hobbiename)
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(     x => x.hobbiename,     Model.hobbiename ) 
        @Html.ValidationMessageFor(model => model.hobbiename)
    </div>

我收到错误：System.MissingMethodException：没有为此对象定义无参数构造函数

Answer 1

我会将它们创建为

<强>型号：

public class ViewModel
{
    public int Id { get; set; }
    public string HobbyName { get; set; }
    public IEnumerable<SelectListItem> Hobbies {get;set; }
    public string FileLocation { get; set; }
    public string HobbyDetail { get; set; }
}

<强>动作

public ActionResult Create()
{
    var someDbObjects= new[]
    { 
        new { Id = "1", Text = "Dancing" },
        new { Id = "2", Text = "Painting" }, 
        new { Id  = "3", Text = "Singing" },
    };
    var model = new ViewModel
    {
       Hobbies = someDbObjects.Select(k => new SelectListItem{ Text = k, Value = k.Id })
    }; 

    return View(model);
}

查看

<div class="editor-label"> @Html.LabelFor(model => model.HobbyName) </div> <div class="editor-field"> @Html.DropDownListFor(x => x.HobbyName, Model.Hobbies ) @Html.ValidationMessageFor(model => model.HobbyName) </div>

Answer 2

您没有将任何模型传递给您的操作中的视图。此外，您不应使用相同的属性作为DropDownListFor助手的第一个和第二个参数。作为lambda表达式传递的第一个参数对应于视图模型上的标量属性，该属性将保存选定的值，并允许您在提交表单时检索此值。第二个参数是集合。

所以你可以调整一下你的代码：

型号：

public class Hobbies
{
    [Required]
    public string SelectedHobbyId { get; set; }
    public IEnumerable<SelectListItem> AvailableHobbies { get; set; }

    ... some other properties that are irrelevant to the question 
}

控制器：

public class HomeController: Controller
{
    public ActionResult Create()
    {
        // obviously those values might come from a database or something
        var values = new[]
        { 
            new { Value = "1", Text = "Dancing" },
            new { Value = "2", Text = "Painting" }, 
            new { Value = "3", Text = "Singing" },
        };

        var model = new Hobbies
        {
           AvailableHobbies = values.Select(x => new SelectListItem
           {
               Value = x.Value,
               Text = x.Text
           });
        }; 
        return View(model);
    }     

    [HttpPost]
    public ActionResult Create(Hobbies hobbies)
    {
        // hobbies.SelectedHobbyId will contain the id of the element
        // that was selected in the dropdown
        ...
    }
}

查看：

@model Hobbies
@using (Html.BeginForm())
{
    @Html.LabelFor(x => x.SelectedHobbyId)
    @Html.DropDownListFor(x => x.SelectedHobbyId, Model.AvailableHobbies) 
    @Html.ValidationMessageFor(x => x.SelectedHobbyId)

    <button type="submit">Create</button>
}

填充mvc3中的下拉列表

2 个答案: