MVC-没有键类型为"IEnumerable< SelectListItem>"的Viewdata项 [英] MVC - No Viewdata item with key of type 'IEnumerable<SelectListItem>'

问题描述

我是MVC和ASP.NET的新手，并且希望学习一些东西，所以我试图制作一些琐碎的应用程序来了解这些细节.

I'm new to MVC and ASP.NET and am looking to learn a bit, so I'm trying to make some trivial applications to learn the ins and outs.

好吧，我正在尝试使一个下拉框显示一本书的列表，在其中可以显示书的标题，但要发布book_id [主键]

Well, I'm trying to make a dropdown box show a list of books where it would show the title of the book but post the book_id [primary key]

我得到的错误是::没有键类型为'IEnumerable'的键'book_id'的ViewData项目.

The error I get is:: There is no ViewData item with the key 'book_id' of type 'IEnumerable'.

这是我的观点:

    <p>
        <label for="book_id">Book:</label>

        <%= Html.DropDownList("book_id" , (IEnumerable<SelectListItem>)ViewData["Books"]) %> 
        <%= Html.ValidationMessage("book_id", "*") %>
    </p>

这是我的控制器中的内容

Here is what's in my controller

        // GET: /Home/Create
//This is the form creation. 
[Authorize]
public ActionResult Create()
{
    this.ViewData["Books"] =
        new SelectList(_entities.BookSet.ToList(), "book_id", "Title");
    return View();
} 

//
// POST: /Home/Create
//This sends it to the DB
[AcceptVerbs(HttpVerbs.Post) , Authorize]
public ActionResult Create([Bind(Exclude="problem_id")] Problem inProblem)
{
    try
    {
        // TODO: Add insert logic here
        Models.User user = getUser(User.Identity.Name);
        if (user != null)
        {
            inProblem.user_id = user.user_id;
        }
        _entities.AddToProblemSet(inProblem);
        _entities.SaveChanges();

        return RedirectToAction("Index");
    }
    catch
    {
        return View();
    }
}

我的图书"表如下所示:

And my Books table looks like this

        book_id
        title
        publisher
        language
        isbn

我认为这是一个新手的小错误；但我算不上什么运气.任何帮助都很好

I'm assuming this is a trivial newbie mistake; but I'm not having much luck figuring it out. Any help would be great

推荐答案

更简单的解决方案是将ViewData元素的名称与下拉列表相同:

Easier solution is to just name the ViewData element the same as the drop down list:

this.ViewData["book_id"] = new SelectList(_entities.BookSet.ToList(), "book_id", "Title"); 

这将自动绑定:

<%= Html.DropDownList("book_id") %>

如果您想再次显示视图(如在捕获中一样)，还需要在Create的Post版本中填充ViewData ["book_id"].

You will also need to populate the ViewData["book_id"] in the Post version of Create if you want to display the view again (as you do in the catch).

[AcceptVerbs(HttpVerbs.Post) , Authorize] 
public ActionResult Create([Bind(Exclude="problem_id")] Problem inProblem) 
{ 
    try 
    { 
        // TODO: Add insert logic here 
        Models.User user = getUser(User.Identity.Name); 
        if (user != null) 
        { 
            inProblem.user_id = user.user_id; 
        } 
        _entities.AddToProblemSet(inProblem); 
        _entities.SaveChanges(); 

        return RedirectToAction("Index"); 
    } 
    catch 
    { 
        this.ViewData["Books"] = new SelectList(_entities.BookSet.ToList(), "book_id", "Title"); 
        // ViewData["book_id"] with example above.

        return View(); 
    } 
} 

注意:上面的this.ViewData ["Books"]应该确实在捕获范围内完成-在那里只是为了演示丢失的内容.

Note: The this.ViewData["Books"] above should really be done within the catch - its just there for demonstration on whats missing.

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