ASP.NET MVC 视图模型未绑定到带有 DropDownList 的 HTTP Post

Question

我遇到一个问题，当我发布到控制器时，我失去了绑定，并且我的视图模型中的所有内容都是 NULL。这是我正在使用的代码：

查看：

@model ArticleCategoryVm

@using (@Html.BeginForm())
{
    @Html.HiddenFor(model => model.LanguageIdDisplayed)

    <label>Name: <span class="label label-important">Required</span></label>
    @Html.HmlValidationFor(model => model.CategoryName)
    @Html.TextBoxFor(model => model.CategoryName, new { maxlength = "255", placeholder = "Category Name", @class = "input-xlarge-fluid" })                  
    <span class="help-block">The is the name of the category and how it appears on the site.</span>

    <label>Language: <span class="label label-important">Required</span></label>
    @Html.HmlValidationFor(model => model.LanguageId)
    @Html.DropDownList("LanguageId", new SelectList(@Model.Languages, "Value", "Text"), "Select language", new { @class="input-xlarge-fluid" })
    <span class="help-block">This will be the language that the category is set too.</span>

    <label>Parent:</label>
    @Html.HmlValidationFor(model => model.CategoryParentId)
    @Html.DropDownList("CategoryParentId", new SelectList(@Model.CategoryParents, "Value", "Text"), new { @class = "input-xlarge-fluid" })
    <span class="help-block">Allows you to group the category under another existing category.</span>

    <label>Moderator Email: <span class="label label-important">Required</span></label>
    @Html.HmlValidationFor(model => model.ModeratorEmail)
    @Html.TextBoxFor(model => model.ModeratorEmail, new { maxlength = "255", placeholder = "Email Address", @class = "input-xlarge-fluid" })
    <span class="help-block">This is the moderator email for articles in this category.</span>

    <button type="submit" class="btn btn-duadua btn-small"><i class="icon-ok-3"></i> Add New Category</button>                      
}

视图模型：

public class ArticleCategoryVm : BaseLayoutVm
{
    public int LanguageIdDisplayed;
    public List<ArticleCategoryItemVm> ArticleCategoryItemVms { get; set; }

    // Add Category Fields
    [Required]
    public string CategoryName;

    [EmailAttribute]
    [Required]
    public string ModeratorEmail;

    [Required]
    public int LanguageId;

    public int CategoryParentId;

    public List<SelectListItem> Languages { get; set; }
    public List<SelectListItem> CategoryParents { get; set; }
}

控制器：

[HttpPost]
public ActionResult Categories(ArticleCategoryVm vm)
{
   // Code here
   if (ModelState.IsValid)
   {
   }

   ReDrawDropDowns(vm);
   return View(vm)
}

为什么我的视图模型中的所有内容都是 NULL？我可以在使用 Chromes 工具时看到，在帖子中为字符串和整数发布了值...作为一种解决方法，我刚刚完成了以下操作以使代码正常工作：

解决方法控制器：

[HttpPost]
public ActionResult Categories(int LanguageIdDisplayed, string CategoryName, string ModeratorEmail, int LanguageId, int CategoryParentId)
{
    var vm = new ArticleCategoryVm()
    {
        CategoryName = CategoryName,
        LanguageIdDisplayed = LanguageIdDisplayed,
        ModeratorEmail = ModeratorEmail,
        LanguageId = LanguageId,
        CategoryParentId = CategoryParentId
    };

    if (ModelState.IsValid)
    {
    }

    ReDrawDropDowns(vm);
    return View(vm)
}

谢谢

Answer 1

要在 View 中建模绑定，您应该使用 strongly-typed-html-helpers

替换

@Html.DropDownList("CategoryParentId", new SelectList(@Model.CategoryParents, "Value", "Text"), new { @class = "input-xlarge-fluid" })

到：

@Html.DropDownListFor(model => model.CategoryParentId, new SelectList(@Model.CategoryParents, "Value", "Text"), new { @class = "input-xlarge-fluid" })

Answer 2

看起来这可能是因为this question 中提到的属性和变量之间的差异。将{ get; set; } 添加到要绑定的所有变量中。如该问题所述，我认为这是因为默认模型绑定器使用反射的方式。

过去我发现实际获取 ASP.NET MVC 源代码很有用，这样我就可以调试它并查看发生了什么。

Answer 3

view model 为NULL还有另一个原因：

• 动作参数中模型的名称与视图模型的属性之一相同

---

例子：

型号：

public class NewBookPageView{
  int blabla {get;set;}
  Book NewBook {get;set;} //NewBook is the same as newBook in action parameter
}

控制者：

[HttpPost]
public ActionResult AddNewBook(NewBookPageView newBook)//newBook is the same as NewBook in view
{
   int temp = newBook.blabla;
   temp++;
   //...
}

---

提示： 这里同名表示不区分大小写（newBook 与 NewBook 相同）

提示：在 MVC3 和 MVC4 中面临。