Question

我收到上面的错误消息。我已经查看了其他问题，似乎无法查明错误。这是我为控制器提供的代码。这是我得到的错误：

System.InvalidOperationException：具有键'RecieverID'的ViewData项的类型为'System.String'，但必须是'IEnumerable＆lt; SelectListItem＆gt;'的类型

public ActionResult Create()
    {
        ViewBag.RecieverID = new SelectList(db.AspNetUsers, "Id", "Email");
        return View();
    }


    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "RecieverID,TEXT")] Message message)
    {
        if (ModelState.IsValid)
        {
            var mes = new Message
            {
                SenderID = User.Identity.GetUserId(),
                DATETIMEMADE = DateTime.Now,
                TEXT = message.TEXT
            };
            db.Messages.Add(mes);
            db.SaveChanges();
            return RedirectToAction("Index");
         }
        ViewBag.ReceiverID = new SelectList(db.AspNetUsers, "Id", "Email", message.RecieverID);
        return View(message);
    }

之后是我创建消息的观点：

@model MUE.Models.Message

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>Message</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })


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



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

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default"   />
            </div>
        </div>
    </div>
}

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

不确定问题的来源，但我们将非常感谢任何帮助。

Answer 1

首先，不要成为纳粹语法，但它应该是“接收者”而不是“接收者”。

其次，model.RecieverID表示单个字段，而不是集合。

“新的SelectList（...”是集合。

请参考： MVC - Set selected value of SelectList

Answer 2

您可以为页面创建一个ViewModel，例如：

public class MyViewModel
{
    public SelectList ReceiverList
    public MUE.Models.Message ReceivedMessage
}

在控制器中分配您的值，然后执行以下操作：

@Html.DropDownListFor(model => model.ReceivedMessage.ReceiverID, Model.ReceiverList, new { @class = "form-control" })

System.InvalidOperationException：提交邮件时

2 个答案: