DropDownListFor选定的值不适用于列表中的属性

Question

我有问题在ASP MVC 4中使用DropDownListFor设置DropDownList的默认选定值.

当我想要预选的属性在列表中时,默认情况下从未按预期选择.

这是我的代码简化为重要的东西:

楷模:

public class Renter
{
    ...
    public virtual List<RentLine> RentLines { get; set; }
    ...

    public Renter()
    {
        ...
        RentLines = new List<RentLine>();
        ...
    }
}

public class RentLine
{
    ...
    public Guid RenterId { get; set; }
    public virtual Renter Renter { get; set; }  
    public Guid GarageId { get; set; }
    public virtual Garage Garage { get; set; }
    ...

    public RentLine()
    {
        //
        // Testcase for default value in dropdownlist
        //
        GarageId = new Guid("e926dcac-05ac-4fc1-92a2-014345e6e11c");
    }
}

控制器:

public ActionResult Hinzufuegen()
{
    var model = new AddRenterViewModel();
    return View(model);
}

视图模型:

public class AddRenterViewModel
{
    public Renter Renter { get; set; }

    public List<SelectListItem> RentableGarageItems { get; set; }

    ...

    public AddRenterViewModel()
    {
        Renter = new Renter();
        Renter.RentLines.Add(new RentLine());

        RentableGarageItems = new List<SelectListItem>();
        foreach (var garage in Singleton.Instance.Entities.GetRentableGarages().OrderBy(g => g.No))
        {
            RentableGarageItems.Add(new SelectListItem{Text = garage.No.ToString(), Value = garage.Id.ToString()});
        }
    }   
}

视图:

@model Grossgaragenverwaltung.ViewModels.AddRenterViewModel
...
Garage Nr. @Html.DropDownListFor(m => m.Renter.RentLines[0].GarageId, Model.RentableGarageItems) @* No selected value *@
           @Html.TextBoxFor(m => m.Renter.RentLines[0].GarageId) @* Shows the id 'e926dcac-05ac-4fc1-92a2-014345e6e11c' as set in the constructor *@
...

结果如下,没有选中的值:

Garage Nr.
<select id="Renter_RentLines_0__GarageId" name="Renter.RentLines[0].GarageId" data-val-required="Das Feld "GarageId" ist erforderlich." data-val="true">
<option value="225a761d-7d12-4e02-9d72-d54fb6934f05">1</option>
<option value="d28fb4fb-d65b-4674-90d6-a4ab9636be80">2</option>
<option value="e06b520b-e876-4870-b321-dc65f77967a7">3</option>
<option value="56832d98-aa5a-4e1a-af44-2d7e00f2bb3a">4</option>
<option value="551f1fa9-13a5-40ce-b795-50063e605027">5</option>
<option value="bace4b40-92ab-4757-9716-2a2878c2c9e8">6</option>
<option value="f9baf45b-96bf-463e-a234-a1522bfc9b9b">7</option>
<option value="91d1d866-6346-4ab0-b2aa-35b56eeaf2b0">8</option>
<option value="62eb3727-eab2-4180-90cd-7dc59119f44e">9</option>
<option value="59768097-c772-4421-b907-a24397a106f5">10</option>
<option value="270acf6b-e4e3-41c3-86dd-4381a313848a">11</option>
<option value="923269cd-1ead-4346-90ce-6344acda5b1b">12</option>
<option value="981ee61e-408b-4b08-a7d3-26c909f04a9d">13</option>
<option value="f1c5043c-fe41-4a8e-8c58-e88363885de4">14</option>
<option value="e926dcac-05ac-4fc1-92a2-014345e6e11c">15</option>
<option value="5577dc00-7cfa-4bcd-99ad-3f356e4325ae">16</option>
</select>
<input id="Renter_RentLines_0__GarageId" type="text" value="e926dcac-05ac-4fc1-92a2-014345e6e11c" name="Renter.RentLines[0].GarageId">

我怎样才能完成这项工作？

更新:这是一个工作示例,其中一切都像预期的那样工作,只有在您看到上面的情况下才会出现问题:

public class Renter
{
    ...
    public Salutation Salutation { get; set; }
    ...

    public Renter()
    {
        ...
        Salutation = Salutation.Male;
        ...
    }
}

public ActionResult Hinzufuegen()
{
    var model = new AddRenterViewModel();
    return View(model);
}

public class AddRenterViewModel
{
    public Renter Renter { get; set; }

    public List<SelectListItem> SalutationItems { get; set; }

    ...

    public AddRenterViewModel()
    {
        Renter = new Renter();
        Renter.RentLines.Add(new RentLine());

        SalutationItems = new List<SelectListItem>();
        foreach (Salutation salutation in Enum.GetValues(typeof(Salutation)))
        {
           SalutationItems.Add(new SelectListItem { Text = NameEnum.GetName(salutation), Value = salutation.ToString() });
        }
    }   
}

@Html.DropDownListFor(m => m.Renter.Salutation, Model.SalutationItems)

<select id="Renter_Salutation" name="Renter.Salutation" data-val-required="Das Feld "Salutation" ist erforderlich." data-val="true">
<option value="Company">Firma</option>
<option value="Male" selected="selected">Männlich</option>
<option value="Female">Weiblich</option>
</select>

Answer 1

经过一些研究后,dropdownlistfor没有在循环中选择正确的值,我找到了一个解决方案.

这有效:

@Html.DropDownListFor(m => m.Renter.RentLines[0].GarageId,
  new SelectList(Model.RentableGarageItems, "Value", "Text", Model.Renter.RentLines[0].GarageId))