無法在Code First Entity Framework的部分視圖中綁定dropdownlist

Question

我是MVC的新手，所以對菜鳥的問題深表歉意！

我有以下模型（TimeEntry），用於輸入時間表詳細信息：

namespace MVCLogin.Models
{
    public class TimeEntry
    {
        public int TimeEntryID { get; set; }
        public int TaskTypeID { get; set; }
        [ForeignKey("TaskTypeID")]
        public virtual TaskType TaskType { get; set; }
        public double MonHours { get; set; }
        public double TueHours { get; set; }
        public double WedHours { get; set; }
        public double ThuHours { get; set; }
        public double FriHours { get; set; }

    }
}

任務類型基於以下模型：

namespace MVCLogin.Models
{
    public class TaskType
    {
        public int TaskTypeID { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
    }
}

我使用以下局部視圖來輸入時間表詳細信息：

<div class="col-md-1">
    @Html.EditorFor(model => model.TaskType)
    @Html.ValidationMessageFor(model => model.TaskType)
</div>
<div class="col-sm-1">
    @Html.TextBoxFor(model => model.MonHours , new { style = "width:100%", @class = "hours mon" })
    @Html.ValidationMessageFor(model => model.MonHours)
</div>
<div class="col-sm-1">
    @Html.TextBoxFor(model => model.TueHours, new { style = "width:100%", @class = "hours tue" })
    @Html.ValidationMessageFor(model => model.TueHours)
</div>
<div class="col-sm-1">
    @Html.TextBoxFor(model => model.WedHours, new { style = "width:100%", @class = "hours wed" })
    @Html.ValidationMessageFor(model => model.WedHours)
</div>
<div class="col-sm-1">
    @Html.TextBoxFor(model => model.ThuHours, new { style = "width:100%", @class = "hours thu" })
    @Html.ValidationMessageFor(model => model.ThuHours)
</div>
<div class="col-sm-1">
    @Html.TextBoxFor(model => model.FriHours, new { style = "width:100%", @class = "hours fri" })
    @Html.ValidationMessageFor(model => model.FriHours)
</div>

我希望任務類型字段為下拉列表，但我不知道如何將其連接起來。 這些類和數據是正確的，就像我為TimeEntry類搭建一個控制器（使用Visual Studio的“添加控制器”工具）一樣，它可以正常工作：

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

如何使下拉列表在局部視圖中工作？

Answer 1

Html.DropDownList的null參數是Dropdown的數據，並且是Ienumerable<SelectList> 。

為了傳遞數據。 您需要將TaskType列表轉換為SelectListItem列表（您可以在Controller或其他地方執行此操作，然后再將Model從Controller發送到View），然后將其放入模型中

namespace MVCLogin.Models
{
    public class TimeEntry
    {
        public int TimeEntryID { get; set; }
        public int TaskTypeID { get; set; }
        [ForeignKey("TaskTypeID")]
        public virtual TaskType TaskType { get; set; }
        public IEnumerable<SelectListItem> TaskTypeSelectListItems { get; set; }
        public double MonHours { get; set; }
        public double TueHours { get; set; }
        public double WedHours { get; set; }
        public double ThuHours { get; set; }
        public double FriHours { get; set; }

    }
}

下拉代碼將更改為

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

請注意，當您發布/獲取到服務器時，所選值將綁定到模型上的“ TaskTypeID”。

Answer 2

根據您的請求：ViewBag是一個屬性，使您可以將控制器中的值動態共享到視圖。 由於它是動態的，因此請記住，您將需要顯式轉換對象，以便剃刀引擎知道它們在運行時的狀態。 請注意，在閱讀有關內容（底部的更多內容）時，ViewBag壽命很短，僅存在於當前請求中，因此，如果控制器中出現模型狀態錯誤，則需要將數據重新加載到視圖包中。

這將有助於保持模型/視圖模型的整潔。

接下來是代碼，測試設置：我有我的主頁（索引），並且有一個局部視圖（AddSomething）被加載到我的主索引頁面中。 給定您的模型，這就是我的控制器的外觀。 請注意，我最初是在父頁面中加載視圖包，但是如果提交時發生錯誤，則由於動態對象存在時間太短，我需要重新加載視圖包。

    DALHelper dalHelp = new DALHelper();

    public ActionResult Index()
    {
        //Get a list of task types from the data access layer
        //Cast them into a SelectItemList and pass them into viewBag
        ViewBag.TaskDD = dalHelp.GetTaskTypes().Select(a => new SelectListItem { Text = a.Name, Value = a.TaskTypeID.ToString() }).ToList();
        return View();
    }

    public ActionResult AddSomething()
    {
        TimeEntry te = new TimeEntry();
        return View(te);
    }

    [HttpPost]
    public ActionResult AddSomething(TimeEntry te)
    {

        if (ModelState.IsValid)
        {
            //call my Data Access Layer to add new entry and redirect to wherver on success 
            if (dalHelp.CreateTimeEntry(te))
            {
                return RedirectToAction("Index");
            }
            else
            {
                //something happened during adding entry into DB, write whatever code to handle it gracefully
                //I need to reload my viewbag since it has since been cleared (short lived)
                ViewBag.TaskDD = dalHelp.GetTaskTypes().Select(a => new SelectListItem { Text = a.Name, Value = a.TaskTypeID.ToString() }).ToList();
                ModelState.AddModelError("TimeEntryID", "An Error was encountered...");
                return View(te);
            }
        }
        else
        {
            //I need to reload my viewbag since it has since been cleared (short lived)
            ViewBag.TaskDD = dalHelp.GetTaskTypes().Select(a => new SelectListItem { Text = a.Name, Value = a.TaskTypeID.ToString() }).ToList();
            return View(te);
        }
    }

在我的局部視圖中，我需要轉換我的viewbag項，因為它是動態類型，因此剃刀引擎可以處理：另外，我不是在使用Dropdownlist而不是dropdownlist：

    @model deletemeweb2.Models.TimeEntry

    @using (Html.BeginForm("AddSomething", "Home")) 
    {
        @Html.AntiForgeryToken()

        <div class="form-horizontal">
            <h4>TimeEntry</h4>
            @Html.ValidationMessageFor(model => model.TimeEntryID, "", new { @class = "text-danger" })

            <hr />
            @Html.ValidationSummary(true, "", new { @class = "text-danger" })
            <div class="form-group">
                @Html.LabelFor(model => model.TaskTypeID, htmlAttributes: new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.DropDownListFor(model => model.TaskTypeID, (IEnumerable<SelectListItem>)ViewBag.TaskDD, new { @class = "form-control" })
                    @Html.ValidationMessageFor(model => model.TaskTypeID, "", new { @class = "text-danger" })
                </div>
            </div>

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

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

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

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

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

有關處理不同控制器需求時有關ViewBag和類似屬性的更多信息，請訪問： http ://www.c-sharpcorner.com/blogs/viewdata-vs-viewbag-vs-tempdata-in-mvc1