ASP.NET MVC3：查看POSTed模型值为NULL

Question

我有以下控制器和视图。它使用GET正确列出值。当我点击按钮时，它会导致POST。但是，控制器中收到的值为NULL。我们如何纠正它？

突出显示的代码

    [HttpPost]
    public ActionResult CastVote(IEnumerable<Program> theProgramList)

获取图片

CODE

 public enum RatingEnum { Poor = 0, Neutral, Good, Excellent };

public class Program
{
    public int ProgramID { get; set; }
    public string ProgramName { get; set; }
    public RatingEnum RatingID { get; set; }
    public string ProgramCategory { get; set; }
}

CONTROLLER

namespace MyProgramRatingApp.Controllers
{
public class ProgramController : Controller
{




    List<Program> programList = new List<Program>()
                          {
                            new Program
                            {
                                ProgramID = 1,ProgramName = "Program1",
                                ProgramCategory = "A"
                            },
                            new Program
                            {
                                ProgramID = 2,ProgramName = "Program2",
                                ProgramCategory = "B"
                            },
                            new Program
                            {
                                ProgramID = 3,ProgramName = "Program3",
                                ProgramCategory = "A"
                            }

                          };




    // GET: /Program/
    public ActionResult CastVote()
    {
        ViewBag.RatingEnum = GetRstingSelectList();
        return View(programList);
    }


    // POST: /StoreManager/Create
    [HttpPost]
    public ActionResult CastVote(IEnumerable<Program> theProgramList)
    {
        if (ModelState.IsValid)
        {
            //Save the book in DB first and then redirectToAction.


            return RedirectToAction("CastVote");
        }

        return View(theProgramList);
    }


    public static SelectList GetRstingSelectList()
    {
        Array values = Enum.GetValues(typeof(RatingEnum));
        List<System.Web.UI.WebControls.ListItem> items = new List<System.Web.UI.WebControls.ListItem>(values.Length);

        foreach (var i in values)
        {
            items.Add(new System.Web.UI.WebControls.ListItem
                                    {
                                        Text = Enum.GetName(typeof(RatingEnum), i),
                                        Value = ((int)i).ToString()
                                    }
                       );
        }

        return new SelectList(items);
    }


    }
}

查看

@model IEnumerable<MyProgramRatingApp.Program>

@{
ViewBag.Title = "CastVote";
}

<h2>CastVote</h2>

@using (Html.BeginForm())
{
<table>
    <tr>
        <th style="border:1px solid Teal; background-color:Gray">
            ProgramName
        </th>
        <th style="border:1px solid Teal; background-color:Gray">
            RatingID
        </th>
        <th style="border:1px solid Teal; background-color:Gray">
            ProgramCategory
        </th>
        <th style="border:1px solid Teal; background-color:Gray"></th>
    </tr>

@foreach (var item in Model)
{
    <tr>
        <td style="border:1px solid Teal">
            @Html.DisplayFor(modelItem => item.ProgramName)
        </td>
        <td style="border:1px solid Teal">
            @Html.DisplayFor(modelItem => item.RatingID)
        </td>
        <td style="border:1px solid Teal">
            @Html.DisplayFor(modelItem => item.ProgramCategory)
        </td>
        <td style="border:1px solid Teal">
            @Html.DropDownListFor(model => item.RatingID, (SelectList)ViewBag.RatingEnum, String.Empty)
        </td>

    </tr>
}

</table>

<p>
    <input type="submit" value="Cast Vote" />
</p>

}

读：

1. dropdownlist set selected value in MVC3 Razor

2. ASP.NET MVC 3 - Partial vs Display Template vs Editor Template

3. IEnumerable property with MVC3 EditorTemplate

4. 用于模型绑定到数组，列表，集合，词典的ASP.NET Wire Format

5. 模型绑定到列表

---

Answer 1

通过调用编辑器模板替换视图中的foreach循环：

@model IEnumerable<MyProgramRatingApp.Program>

@{
    ViewBag.Title = "CastVote";
}

<h2>CastVote</h2>

@using (Html.BeginForm())
{
    <table>
        <tr>
            <th style="border:1px solid Teal; background-color:Gray">
                ProgramName
            </th>
            <th style="border:1px solid Teal; background-color:Gray">
                RatingID
            </th>
            <th style="border:1px solid Teal; background-color:Gray">
                ProgramCategory
            </th>
            <th style="border:1px solid Teal; background-color:Gray"></th>
        </tr>

        @Html.EditorForModel()

    </table>

    <p>
        <input type="submit" value="Cast Vote" />
    </p>
}

然后定义将为模型中的每个元素自动呈现的编辑器模板（~/Views/Shared/EditorTemplates/Program.cshtml）：

@model MyProgramRatingApp.Program
<tr>
    <td style="border:1px solid Teal">
        @Html.EditorFor(x => x.ProgramName)
    </td>
    <td style="border:1px solid Teal">
        @Html.EditorFor(x => x.RatingID)
    </td>
    <td style="border:1px solid Teal">
        @Html.EditorFor(x => x.ProgramCategory)
    </td>
    <td style="border:1px solid Teal">
        @Html.DropDownListFor(
             x => x.RatingID, 
             (SelectList)ViewBag.RatingEnum, 
             String.Empty
        )
    </td>
</tr>

请注意，我在编辑器模板中使用了@Html.EditorFor而不是@Html.DisplayFor来生成输入字段。如果不这样做，则不会在控制器中返回任何值，因为表单不包含任何输入元素。如果您不想显示输入字段，可以使用隐藏的输入：

@model MyProgramRatingApp.Program
<tr>
    <td style="border:1px solid Teal">
        @Html.DisplayFor(x => x.ProgramName)
        @Html.HiddenFor(x => x.ProgramName)
    </td>
    <td style="border:1px solid Teal">
        @Html.DisplayFor(x => x.RatingID)
        @Html.HiddenFor(x => x.RatingID)
    </td>
    <td style="border:1px solid Teal">
        @Html.DisplayFor(x => x.ProgramCategory)
        @Html.HiddenFor(x => x.ProgramCategory)
    </td>
    <td style="border:1px solid Teal">
        @Html.DropDownListFor(
             x => x.RatingID, 
             (SelectList)ViewBag.RatingEnum, 
             String.Empty
        )
    </td>
</tr>

编辑器模板将为输入字段生成正确的名称，以便模型绑定器正确绑定值。

您还可以查看following article，以便更好地了解集合所需的有线格式。

Answer 2

这段代码对我有用：

1. 控制器： [HttpPost] public ActionResult CastVote（Ilist theProgramList）

2查看：

@model IList<Program>
@using (Html.BeginForm())
{
<table>
    <tr>
        <th style="border:1px solid Teal; background-color:Gray">
            ProgramName
        </th>
        <th style="border:1px solid Teal; background-color:Gray">
            ProgramCategory
        </th>
        <th style="border:1px solid Teal; background-color:Gray">  </th>
    </tr>

@for(var i=0,j=mode.Count;i<j;i++)
{
  <tr>
     <td>@model[i].ProgrameName</td>
     <td><input type="text" name="RaingID[@i]" value="@model[i].RatingID"</td>


      <td>
        @Html.DropDownListFor(x => x.Rating, 
                      (SelectList)ViewBag.RatingEnum, new {@name="ProgramCategory[i] "})
     </td>
  </tr>
}
<p>
    <input type="submit" value="Cast Vote" />
</p>

</table>

}

Answer 3

感谢达林。我接受了他的回答。发布完整的解决方案是为了其他人的利益。

注意：EditorTemplate有助于避免foreach循环并帮助正确的对象绑定。

注意：EditorTemplate应放在适当的文件夹中，文件名应基于约定。

//模型

namespace MyProgramRatingApp
{
public enum RatingEnum { Poor = 0, Neutral, Good, Excellent };

public class Program
{
    public int ProgramID { get; set; }
    public string ProgramName { get; set; }
    public RatingEnum Rating { get; set; }
    public string ProgramCategory { get; set; }
}
}

//控制器

using System;
using System.Collections.Generic;
using System.Web.Mvc;

namespace MyProgramRatingApp.Controllers
{

public class ProgramController : Controller
{


    List<Program> programList = new List<Program>()
                          {
                            new Program
                            {
                                ProgramID = 1,ProgramName = "Program1",
                                ProgramCategory = "A"
                            },
                            new Program
                            {
                                ProgramID = 2,ProgramName = "Program2",
                                ProgramCategory = "B"
                            },
                            new Program
                            {
                                ProgramID = 3,ProgramName = "Program3",
                                ProgramCategory = "A"
                            }

                          };




    // GET: /Program/
    public ActionResult CastVote()
    {
        ViewBag.RatingEnum = GetRstingSelectList();
        return View(programList);
    }


    // POST: /StoreManager/Create
    [HttpPost]
    public ActionResult CastVote(IEnumerable<Program> theProgramList)
    {
        if (ModelState.IsValid)
        {
            //Save the book in DB first and then redirectToAction.
            return RedirectToAction("CastVote");
        }

        return View(theProgramList);
    }


    public static SelectList GetRstingSelectList()
    {
        Array values = Enum.GetValues(typeof(RatingEnum));
        List<System.Web.UI.WebControls.ListItem> items = new List<System.Web.UI.WebControls.ListItem>(values.Length);

        foreach (var i in values)
        {
            items.Add(new System.Web.UI.WebControls.ListItem
                                    {
                                        Text = Enum.GetName(typeof(RatingEnum), i),
                                        Value = ((int)i).ToString()
                                    }
                       );
        }

        return new SelectList(items);
    }


 }
}

查看（CastVote.cshtml）

@model IEnumerable<MyProgramRatingApp.Program>

@{
ViewBag.Title = "CastVote";
}

<h2>CastVote</h2>

@using (Html.BeginForm())
{
<table>
    <tr>
        <th style="border:1px solid Teal; background-color:Gray">
            ProgramName
        </th>
        <th style="border:1px solid Teal; background-color:Gray">
            ProgramCategory
        </th>
        <th style="border:1px solid Teal; background-color:Gray">  </th>
    </tr>

    @Html.EditorForModel()

</table>

<p>
    <input type="submit" value="Cast Vote" />
</p>
}

EditorTemplate（Program.cshtml）

@model MyProgramRatingApp.Program
<tr>
<td style="border:1px solid Teal">
    @Html.DisplayFor(x => x.ProgramName)
    @Html.HiddenFor(x => x.ProgramName)
</td>
<td style="border:1px solid Teal">
    @Html.EditorFor(x => x.ProgramCategory)
</td>
<td style="border:1px solid Teal">
    @Html.DropDownListFor(x => x.Rating, (SelectList)ViewBag.RatingEnum, String.Empty)
</td>
<td>
    @Html.HiddenFor(x => x.ProgramID)
</td>

</tr>