C# 没有类型为'；IEnumerable<；选择列表项>'；那有关键的AnnouncementId

我试图做一个表格，用下拉列表和一个输入文本的框进行更新，但标题中不断出现错误。它直接从create cshtml中复制

Index.cshtml：

 @model Announcements1.Models.Comment



<div id="CommentDiv"></div>
<div id="CommentCreateForm">

        @using (Ajax.BeginForm("AjaxCreate", "Comments",
                                new AjaxOptions
                                {
                                    InsertionMode = InsertionMode.Replace,
                                    HttpMethod = "POST",
                                    UpdateTargetId = "CommentDiv"
                                }))
        {

            @Html.ValidationSummary(true, "", new { @class = "text-danger" })
            <div class="form-group">
                @Html.LabelFor(model => model.CommentContent, htmlAttributes: new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.EditorFor(model => model.CommentContent, new { htmlAttributes = new { @class = "form-control" } })
                    @Html.ValidationMessageFor(model => model.CommentContent, "", new { @class = "text-danger" })
                </div>
            </div>

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


@section Scripts {
    <script src="~/Scripts/jquery.unobtrusive-ajax.min.js"></script>
    <script src="~/Custom_Scripts/BuildCommentTable.js"></script>
    @Scripts.Render("~/bundles/jqueryval")
  }

和我的JS文件：

    $(document).ready(function () {
    $.ajax({
        url: '/Comments/BuildCommentTable',
        success: function (result) {
            $('#CommentDiv').html(result);
        }
    });

});

---

首先，您缺少在

BuildCommentTable

操作中填充Annouments DropDownList数据的代码，请在返回视图之前添加它，就像在Post操作中一样

其次，如果将ViewBag键命名为与模型属性相同的名称，则两个操作都应具有ViewBag填充，如：

ViewBag.AnnouncementOptions= new SelectList(db.Announcements, "AnnouncementId", "AnnouncementContent", comment.AnnouncementId);

因此，您的get操作将如下所示：

public ActionResult BuildCommentTable()
{
     ViewBag.AnnouncementOptions= new SelectList(db.Announcements, "AnnouncementId", "AnnouncementContent");
     var comments = db.Comments.Include(c => c.Announcement);
     return PartialView("_CommentTable", GetMyComments());
}

以同样的方式更改后期操作方法

ViewBag

总体代码部分：

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult AjaxCreate([Bind(Include = "CommentId,CommentContent,AnnouncementId")] Comment comment)
{
    if (ModelState.IsValid)
    {
        db.Comments.Add(comment);
        db.SaveChanges();
    }

    ViewBag.AnnouncementOptions = new SelectList(db.Announcements, "AnnouncementId", "AnnouncementContent", comment.AnnouncementId);
    return PartialView("_CommentTable", db.Comments.Include(c => c.Announcement));
}

现在在您看来，您应该能够通过以下方式使用强类型助手方法

DropDownListFor

：

<div class="col-md-10">
  @Html.DropDownListFor(x=>x.AnnouncementId, ViewBag.AnnouncementOptions as SelectList, htmlAttributes: new { @class = "form-control" })
  @Html.ValidationMessageFor(model => model.AnnouncementId, "", new { @class = "text-danger" })
</div>

@DropDownListFor（x=>x.AnnouncementId，ViewBag.AnnouncementOptions作为SelectList，htmlAttributes:new{@class=“form control”}）
@Html.ValidationMessageFor（model=>model.AnnouncementId，“，new{@class=“text danger”}）

---

希望对您有所帮助。

您搜索过吗？：@EhsanSajjad是的，但我无法找出问题所在该错误表示

@Html中的
AnnouncementId
。DropDownList（“AnnouncementId”，null，…）

为

null

谢谢！我得到的唯一问题是buildCommentTable中没有对最后一个参数“comment”的引用。您可以删除它，它是一个可选参数。不幸的是，即使您进行了编辑，我仍然会得到一个错误，@html.dropDownListFor上没有具有键“AnnouncementId”的“IEnumerable”类型的ViewData项。在@html.dropdownlistfor行中

<div class="col-md-10">
  @Html.DropDownListFor(x=>x.AnnouncementId, ViewBag.AnnouncementOptions as SelectList, htmlAttributes: new { @class = "form-control" })
  @Html.ValidationMessageFor(model => model.AnnouncementId, "", new { @class = "text-danger" })
</div>