C# 无法获取@Html.DropDownList的值

我有一个创建cshtml页面，如下所示：-

@model MvcCommons.ViewModels.CompositeViewModel
@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

<script src="@Url.Content("~/Scripts/jquery.validate.min.js")"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")"></script>


@using (Html.BeginForm()) {
@Html.ValidationSummary(true)

<fieldset>
    <legend>Article</legend>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleTitle)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleTitle)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleTitle)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleDate)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleDate)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleDate)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleText)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleText)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleText)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleSource)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleSource)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleSource)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.CategoryID, "Category")
    </div>
    <div class="editor-field">
        @Html.DropDownList("CategoryID", String.Empty)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.CategoryID)
    </div>

    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

        [HttpPost]
    public ActionResult Create(CompositeViewModel viewModel)
    {
        if (ModelState.IsValid)
        {
            unitOfWork.ArticleRepository.Insert(viewModel.ArticleViewModel.Article);
            unitOfWork.Save();
            return RedirectToAction("Index");
        }

        PopulateDropDownList(viewModel.ArticleViewModel.Article.CategoryID);
        return View(viewModel);
    }

        private void PopulateDropDownList(object selectedCategory = null)
    {
        var categoryQuery = unitOfWork.CategoryRepository.Get(
                        orderBy: q => q.OrderBy(d => d.CategoryTitle));
        ViewBag.CategoryID = new SelectList(unitOfWork.CategoryRepository.Get(), "CategoryID", "CategoryTitle", selectedCategory);

    }

填充的ROPDownlist代码如下所示：-

@model MvcCommons.ViewModels.CompositeViewModel
@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

<script src="@Url.Content("~/Scripts/jquery.validate.min.js")"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")"></script>


@using (Html.BeginForm()) {
@Html.ValidationSummary(true)

<fieldset>
    <legend>Article</legend>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleTitle)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleTitle)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleTitle)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleDate)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleDate)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleDate)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleText)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleText)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleText)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.ArticleSource)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ArticleViewModel.Article.ArticleSource)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.ArticleSource)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ArticleViewModel.Article.CategoryID, "Category")
    </div>
    <div class="editor-field">
        @Html.DropDownList("CategoryID", String.Empty)
        @Html.ValidationMessageFor(model => model.ArticleViewModel.Article.CategoryID)
    </div>

    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

        [HttpPost]
    public ActionResult Create(CompositeViewModel viewModel)
    {
        if (ModelState.IsValid)
        {
            unitOfWork.ArticleRepository.Insert(viewModel.ArticleViewModel.Article);
            unitOfWork.Save();
            return RedirectToAction("Index");
        }

        PopulateDropDownList(viewModel.ArticleViewModel.Article.CategoryID);
        return View(viewModel);
    }

        private void PopulateDropDownList(object selectedCategory = null)
    {
        var categoryQuery = unitOfWork.CategoryRepository.Get(
                        orderBy: q => q.OrderBy(d => d.CategoryTitle));
        ViewBag.CategoryID = new SelectList(unitOfWork.CategoryRepository.Get(), "CategoryID", "CategoryTitle", selectedCategory);

    }

我的问题是，无论我在下拉列表中选择什么值，CompositeViewModel viewModel中的CategoryID始终为0！在Create cshtml中输入的其他数据在viewModel中正确填充

我看不出我做错了什么

谢谢你的帮助和时间

你应该写信

@Html.DropDownList("ArticleViewModel.Article.CategoryID", ViewBag.CategoryID, null)

因此ModelBinding工作正常，甚至可以使用

DropDownListFor（）

您不应该使用：

---

在为下拉列表生成的HTML中，是否有

name

属性？我遇到了以下错误：-“没有类型为'IEnumerable'的ViewData项具有键'ArticleViewModel.Article.CategoryID'。”我将PopulateDropDownList方法改为包含“ArticleViewModel.Article.CategoryID”而不是“CategoryID”我还按照您的建议在cshtml中对其进行了更改。对不起，我忘记将第二个参数设置为

ViewBag.CategoryID

。我已经编辑了我的帖子。我现在收到这个错误“'System.Web.Mvc.HtmlHelper'没有名为'DropDownListFor'的适用方法，但似乎有一个同名的扩展方法。”ok的工作方式如下@Html.DropDownListFor（model=>model.ArticleViewModel.Article.CategoryID，（SelectList）ViewBag.CategoryID）。既然这两个答案都是有效答案，我现在应该接受什么答案？@Johann Ah对不起，是的

ViewBag.CategoryID

将是

对象

，忘了施放。“我现在应该接受什么样的答案……”这取决于你，选择你认为对你帮助最大的答案。但对丹尼尔不公平，因为他也做出了很多贡献。我给了他一个代表，虽然我不知道那是什么意思：）@Johann两个答案都给了你想要的。如果您想让我比较答案，我唯一想说的是使用

DropDownListFor

更可靠，因为您让框架完成工作，而不是硬编码ID。根据@DanielB的回答，如果你改变了你的模型，你还需要更新你的视图，这很痛苦，而且很容易错过。它也更符合您现有的代码。