如何编写模型的“创建”视图？

I have a many-to-many field in Menu model named Roles, i'm trying to create a 'create' view for the model.

我在Menu模型中有一个名为Roles的多对多字段，我正在尝试为模型创建一个“创建”视图。

my create action methods:

我的创建动作方法：

    public ActionResult Create()
    {
        ViewBag.ParentMenuId = new SelectList(_db.Menus, "Id", "Name");
        ViewBag.Roles = new SelectList(_db.UserRoles.ToList(), "Id", "Name");
        return View();
    }

    [HttpPost]
    public ActionResult Create(Menu menu)
    {
        if (ModelState.IsValid)//the state is always **invalid**
        {
            _db.Menus.Add(menu);
            _db.SaveChanges();
            return RedirectToAction("Index");
        }
        ViewBag.ParentMenuId = new SelectList(_db.Menus, "Id", "Name", menu.ParentMenuId);
        return View(menu);
    }

my view(Create.cshtml):

我的观点（Create.cshtml）：

    <div class="editor-label">
        @Html.LabelFor(model => model.Roles, "Roles")
    </div>
    <div class="editor-field">
        @Html.ListBox("Roles")
        @Html.ValidationMessageFor(model => model.Roles)
    </div>

how to fix it? I'm getting the following error:

怎么解决？我收到以下错误：

The ViewData item that has the key '' is of type '' but must be of type 'IEnumerable<SelectListItem>'

具有键''的ViewData项的类型为''，但必须是'IEnumerable 类型的'

2 个解决方案

#1

Well, the error message is rather clear, you nead a IEnumerable<SelectListItem>

好吧，错误信息相当清楚，你有一个IEnumerable

So change your ViewBag.Roles definition from

所以改变你的ViewBag.Roles定义

new SelectList(_db.UserRoles.ToList(), "Id", "Name");

至

_db.UserRoles.ToList().Select(m => new SelectListItem { Value=m.Id, Text=m.Name});

Edit

编辑

In your view :

在你看来：

@Html.ListBox("Roles", (IEnumerable<SelectListItem>)ViewBag.Roles)

Edit2

EDIT2

You have a model binding problem

你有一个模型绑定问题

In your view

在你看来

@Html.ListBox("selectedRoles", (IEnumerable<SelectListItem>)ViewBag.Roles)

in your Post Action, try to add a new parameter :

在你的Post Action中，尝试添加一个新参数：

[HttpPost]
    public ActionResult Create(Menu menu, int[] selectedRoles)

and treat each selected role "manually" in your action code.

并在您的操作代码中“手动”处理每个选定的角色。

EDIT

编辑

ViewModel sample (not working as is) In your view, you need

ViewModel示例（不按原样工作）在您的视图中，您需要

a DropDownList (ParentMenuId)

DropDownList（ParentMenuId）
a ListBox (RoleIDs)

ListBox（RoleIDs）
the result of this listBox (model binding for the post action)

这个listBox的结果（post动作的模型绑定）
other properties of the Menu class (maybe not all)

Menu类的其他属性（可能不是全部）

The idea would be to create a

想法是创建一个

public class MenuViewModel 
{
  public IEnumerable<SelectListItem> ParentMenuList {get;set;}//a dropDown
  public IEnumerable<SelectListItem> RoleList {get;set;}//a listBox
  public string Name {get;set;}//the menu name //the menu name
  public List<int> SelectedRoles {get;set;}
}

then your get Action would be

然后你的行动将是

public ActionResult Create()
{
  var model = new MenuViewModel();
  model.ParentMenuList = new SelectList(_db.Menus, "Id", "Name");
  model.RoleList = new SelectList(_db.UserRoles.ToList(), "Id", "Name");
  return View(model);
}

your view would have MenuViewModel... as model

您的视图将具有MenuViewModel ...作为模型

@model MenuViewModel
//your other code
//the listbox
 <div class="editor-label">
        @Html.LabelFor(model => model.SelectedRoles, "Roles")
    </div>
    <div class="editor-field">
        @Html.ListBoxFor(m => m.SelectedRoles, Model.RoleList)
        @Html.ValidationMessageFor(model => model.Roles)
    </div>

then your POST action would become

然后你的POST动作就会变成

[HttpPost]
public ActionResult Create(MenuViewModel model)
{
    if (ModelState.IsValid)
    {
       var menu = new Menu {Name = model.Name };//for example
       menu.Roles =  _db.UserRoles.Where(rl => model.SelectedRoles.Contains(rl.Id)).ToList();
       _db.SaveChanges();
       return RedirectToAction("Index");
    }
    return View(model);
}

Pro ViewModel :

Pro ViewModel：

you're just using the properties you need.

你只是使用你需要的属性。
you don't need ViewBag (which is nice to avoid : it's dynamic, not strongly typed, so... hard to test, refactoring problems, etc.)

你不需要ViewBag（这是很好的避免：它是动态的，不是强类型的，所以......很难测试，重构问题等等）
everything is in your view's model

一切都在你视图的模型中

Cons ViewModel :

缺点ViewModel：

you have to map your Model to your ViewModel in the get action, and map from ViewModel to Model in post action, but... it's worse the price !
你必须在get动作中将你的Model映射到ViewModel，并在post动作中从ViewModel映射到Model，但是......它的价格更差！

#2

-1

I was create same project but i don't get that error.

我是创建相同的项目，但我没有得到该错误。

It seems model of listbox was bound to another type, try to specify explicitly viewbag model like this:

似乎列表框的模型绑定到另一个类型，尝试明确指定viewbag模型，如下所示：

@Html.ListBox("Roles",ViewBag.Roles as SelectList)

And in [HttpPost] method try to add ViewBag.Roles which exists in Create - get method, like this:

并在[HttpPost]方法中尝试添加存在于Create - get方法中的ViewBag.Roles，如下所示：

[HttpPost]
    public ActionResult Create(Menu menu)
    {
        if (ModelState.IsValid)//the state is always **invalid**
        {
            _db.Menus.Add(menu);
            _db.SaveChanges();
            return RedirectToAction("Index");
        }
        ViewBag.ParentMenuId = new SelectList(_db.Menus, "Id", "Name", menu.ParentMenuId);
        ViewBag.Roles = new SelectList(_db.UserRoles.ToList(), "Id", "Name");
        return View(menu);
    }

#1