There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key 'listname'.

Question

mvc 中, AbcController 代码：

        public ActionResult Create()
        {
            List<SelectListItem> items = new List<SelectListItem>()
            {
                new SelectListItem(){Text="A", Value="a1", Selected = true},
                new SelectListItem(){Text="B", Value="b1"},
            };

            ViewData["listname"] = new SelectList(items, "Value", "Text");
            return View();
        }

        [HttpPost]
        public ActionResult Create(FormCollection fc)
        {
             Response.Write("<script type='text/javascript'>alert('aaa');</script >");
                return View();
        }

Answer 1

在 view cshtml文件中

@Html.DropDownList("listname")

运行后，submit 报错：

There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key 'listname'.

Answer 2

应该是 @ViewData["listname"]  ，而不是"listname"

---

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Answer 3

谢谢，不行啊

Answer 4

谢谢，不行啊

1）请问你的View页面还是指“Create”那个页面吗？

2）给出你的View的全部代码，谢谢。

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Answer 5

model：

public class RegisterViewModel
    {
        public IEnumerable<SelectListItem> aaa { get ; set; }
    }

view：

@model test.Models.RegisterViewModel

@using (Html.BeginForm("Register", "Account", FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
    @Html.DropDownListFor(m => m.aaa, ViewData["d"] as SelectList)
    <input type="submit" class="btn btn-default" value="注册" />
}

controls：

        public ActionResult Register()
        {
            List<SelectListItem> items = new List<SelectListItem>()
            {
                new SelectListItem(){Text="a", Value="a1", Selected = true},
                new SelectListItem(){Text="b", Value="b1"},
            };
 
            ViewData["d"] = new SelectList(items, "Value", "Text");            
            return View();
        }
 
        [HttpPost]
        public async Task<ActionResult> Register(RegisterViewModel model)
        {

            //这里如何取到被选中的text

         }

Answer 6

请仔细看你的HTML生成源代码，记住<select>标签的name，然后如下替换：

public class FormModel
{
    public string YourSelectTagName{get;set;}
}

  [HttpPost]
        public async Task<ActionResult> Register(FormModel model)
        {
               //处理你的逻辑……
         }

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Answer 7

model，如果改为：

    public class RegisterViewModel
    {
        public string aaa { get; set; }
    }

提示错误：
The ViewData item that has the key 'aaa' is of type 'System.String' but must be of type 'IEnumerable<SelectListItem>'.”

Answer 8

你错误理解我的意思了。你的Select生成的HTML代码应该如下：

<select name="aaa">
  <option value="1">A</aoption>
</select>

那么你不能修改RegisterModel，而是必须额外地增加一个Model，用于进行对于Select提交的数据绑定。请严格按照我的上面代码。

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Answer 9

现在html如下：

<select id="aaa" name="aaa">
<option value="a1">a</option>
<option value="b1">b</option>
</select>

那额外地增加一个Model，要怎么写啊

Answer 10

 [HttpPost]
        public ActionResult Create(FormModel fm)
        {
            //Do your logic here.
        }

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Answer 11

控制器中，原来就有 get 和 post 的 Register代码 ，难道还要再创建 一个 post 的 Register 。

还是不能理解您的意思，能不能给个比较完整的代码？

Answer 12

或者给个参考的博文。

查了很多，都没有解决问题，我也知道，用json，很容易传到后台。

Answer 13

根据你View生成的HTML创建一个新的Model，然后作为Post提交。

其中属性名称必须和form中每一项的name对应。

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Answer 14

model：

    public class RegisterViewModel
    {
        public IEnumerable<SelectListItem> aaa { get; set; }        

    }
    public class FormModel
    {
        public string aaa { get; set; }
    }

controller：

public ActionResult Register()
        {
            List<SelectListItem> items = new List<SelectListItem>()
            {
                new SelectListItem(){Text="a", Value="a1", Selected = true},
                new SelectListItem(){Text="b", Value="b1"},
            };

            ViewData["d"] = new SelectList(items, "Value", "Text");

            return View();
        }

        //
        // POST: /Account/Register
        [HttpPost]
        public ActionResult Register(RegisterViewModel m,FormModel model)
        {
            Response.Write("<script type='text/javascript'>alert('" + model.aaa.ToString() + " ');</script >");
            //这里还是无法取到被选中的值
            return View();

        }

view：

@Html.DropDownListFor(
    x => x.aaa,
    ViewData["d"] as IEnumerable<SelectListItem>,
    "-- select a reason --"
)

Answer 15

view 中，要怎么调用

FormModel

Answer 16

为什么你的Register有2个Model？只需要一个FormModel啊。请先保证无参数的那个Register返回的View生成的Select的HTML的name是“aaa”。

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Answer 17

view：

            @Html.DropDownListFor(d => d.aaa, Model.Select,"-- select --")

生成后的html：

            <select id="aaa" name="aaa"><option value="">-- select --</option>
<option selected="selected" value="a1">a</option>
<option value="b1">b</option>
</select>

model：

    public class RegisterViewModel
    {
        public IEnumerable<SelectListItem> Select { get; set; }
        public string aaa { get; set; }

    }

controls：

        public ActionResult Register()
        {
            RegisterViewModel rv = new RegisterViewModel();
            rv.Select = new List<SelectListItem>()
            {
                new SelectListItem(){Text="a", Value="a1", Selected = true},
                new SelectListItem(){Text="b", Value="b1"},
            };

            return View(rv);
        }
        
        [HttpPost]
        public ActionResult Register(RegisterViewModel m)
        {
            Response.Write("<script type='text/javascript'>alert('" + m.aaa + " ');</script >");
            return View();
        }

提交后报错：

@Html.DropDownListFor(m => m.aaa, Model.Select, "-- select --")

异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。

Answer 18

网上看了很多，在mv3，mv4的好像都能解决问题。本程序是mv5，很多都通不过。郁闷中

Answer 19

终于搞定了，ThankfulHeart

云里雾里的解答，还是要说声谢谢！

Answer 20

MVC work different than ASP.Net, you need to rebind you model in Post action once again and pass it to your view.

          List<SelectListItem> generateList()
        {
            return new List<SelectListItem>()
            {
                new SelectListItem(){Text="a", Value="a1", Selected = true},
                new SelectListItem(){Text="b", Value="b1"},
            };
        }
 public ActionResult Register()
        {
            RegisterViewModel rv = new RegisterViewModel();
            rv.Select =  generateList();

            return View(rv);
        }
        
        [HttpPost]
        public ActionResult Register(RegisterViewModel m)
        {
            RegisterViewModel rv = new RegisterViewModel();
            rv.Select =  generateList();

            Response.Write("<script type='text/javascript'>alert('" + m.aaa + " ');</script >");
            return View(rv);
        }