html.hiddenfor禁用了具有默認值MVC的下拉列表

Question

我已經編輯了de Create視圖，以添加一個隱藏的字段控件，但是我無法獲取該值

<div class="form-group">
   @Html.LabelFor(model => model.EmpresaId, "Empresa", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownList("EmpresaId", null, htmlAttributes: new { @class = "form-control", @disabled = "disabled" })
            @Html.HiddenFor(model => model.EmpresaId)
            @Html.ValidationMessageFor(model => model.EmpresaId, "", new { @class = "text-danger" })
        </div>
</div>

創建的html是：

    <div class="form-group">
        <label class="control-label col-md-2" for="EmpresaId">Empresa</label>
        <div class="col-md-10">
            <select class="form-control" disabled="disabled" id="EmpresaId" name="EmpresaId">
              <option selected="selected" value="1">Farmacia MZ</option>
              <option value="2">Credesa</option>
            </select>
            <input length="19" id="EmpresaId" name="EmpresaId" type="hidden" value="">
            <span class="field-validation-valid text-danger" data-valmsg-for="EmpresaId" data-valmsg-replace="true"></span>
        </div>
    </div>

如您所見，隱藏的輸入沒有任何價值。

在Controller上設置了DropDownList默認值：

public ActionResult Create()
    {
        ApplicationUser usr = db.Users.Find(User.Identity.GetUserId().ToString());
        int userId = (int)usr.EmpresaId;
        ViewBag.CategoriaId = new SelectList(db.Categorias, "CategoriaId", "Nombre");
        ViewBag.EmpresaId = new SelectList(db.Empresas, "EmpresaId", "Nombre", userId); <-- defalut value for disabled DropDownList
        ViewBag.MarcaId = new SelectList(db.Marcas, "MarcaId", "Nombre");
        return View();
    }

我已經搜索了很多，但是我不明白這是什么錯誤。 幫助很好！

Answer 1

此HiddenFor幫助程序顯然HiddenFor到EmpresaId viewmodel屬性：

@Html.HiddenFor(model => model.EmpresaId)

隱藏字段值具有空值，因為它沒有從GET操作方法中的相應viewmodel屬性分配，因為實際上是將EmpresaId默認值分配給包含SelectList ViewBag.EmpresaId 。

ViewBag.EmpresaId = new SelectList(db.Empresas, "EmpresaId", "Nombre", userId);

因此，您需要創建一個viewmodel實例，然后將默認值分配給viewmodel屬性並返回到GET操作方法中的視圖：

// create new instance of viewmodel and set default property value
var model = new ViewModel();
model.EmpresaId = userId;

// return default values from viewmodel to view page
return View(model);

或者只是在創建視圖模型實例時設置默認值：

var model = new ViewModel()
{
    EmpresaId = userId;
};

return View(model);

附帶說明一下，請始終使用強類型的DropDownListFor輔助方法代替DropDownList來綁定viewmodel屬性：

@Html.DropDownListFor(m => m.EmpresaId, ViewBag.EmpresaList as SelectList, new { @class = "form-control", @disabled = "disabled" })