asp.net-mvc HttpPost 上的 ASP.NET MVC DropDownList 值
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ASP.NET MVC DropDownList value on HttpPost
提问by Philip Tenn
I am following this Tutorial on ASP.NET MVC, specifically where it states that providing the String of "MovieType"to the Razor View as follows:@Html.DropDownList("MovieType")will provide the key to DropDownListto find a property in the ViewBagof type IEnumerable<SelectListItem>.
我正在关注ASP.NET MVC 上的这个教程，特别是它指出将字符串提供"MovieType"给 Razor 视图如下：@Html.DropDownList("MovieType")将提供DropDownList的键以查找ViewBag类型中的属性IEnumerable<SelectListItem>。
That works just fine.
这工作得很好。
However, I am unable to get the value that the User selects on my method with [HttpPost]attribute.
但是，我无法获得用户在我的具有[HttpPost]属性的方法上选择的值。
Here is my code and what I have tried thus far.
这是我的代码以及迄今为止我尝试过的代码。
Controller
控制器
public class ProductController : Controller
{
private readonly ProductRepository repository = new ProductRepository();
// Get: /Product/Create
public ActionResult Create()
{
var categories = repository.FindAllCategories(false);
var categorySelectListItems = from cat in categories
select new SelectListItem()
{
Text = cat.CategoryName,
Value = cat.Id.ToString()
};
ViewBag.ListItems = categorySelectListItems;
return View();
}
[HttpPost]
public ActionResult Create(Product product)
{
/** The following line is not getting back the selected Category ID **/
var selectedCategoryId = ViewBag.ListItems;
repository.SaveProduct(product);
return RedirectToAction("Index");
}
}
Razor cshtml View
剃刀 cshtml 视图
@model Store.Models.Product
<h2>Create a new Product</h2>
@using (@Html.BeginForm())
{
<p>Product Name:</p>
@Html.TextBoxFor(m => m.ProductName)
<p>Price</p>
@Html.TextBoxFor(m => m.Price)
<p>Quantity</p>
@Html.TextBoxFor(m => m.Quantity)
<p>Category</p>
@Html.DropDownList("ListItems")
<p><input type="submit" value="Create New Product"/></p>
}
I tried playing with the overloads for DropDownList, but I am not able to get the value back that the User is selecting.
我尝试使用 的重载DropDownList，但我无法取回用户选择的值。
If anyone sees what I am missing or has any ideas or suggestions, I would be very grateful. Thanks!
如果有人看到我遗漏的内容或有任何想法或建议，我将不胜感激。谢谢！
Update
更新
Posting ProductModel. Note, this was auto-generated by Entity Framework when I created the .edmx.
发布Product模型。请注意，这是在我创建 .edmx 时由实体框架自动生成的。
namespace Store.Models
{
using System;
using System.Collections.Generic;
public partial class Product
{
public long Id { get; set; }
public string ProductName { get; set; }
public decimal Price { get; set; }
public int Quantity { get; set; }
public System.DateTime DateAdded { get; set; }
public Nullable<long> CategoryId { get; set; }
public virtual Category Category { get; set; }
}
}
回答by Peter Gluck
You are passing a model of type Store.Models.Productinto your view. The other fields are binding to this model using a lambda expression, but @Html.DropDownList()does not bind to the model so when the model is returned in the HTTPPost the selection is not there.
您正在将类型模型传递Store.Models.Product到您的视图中。其他字段使用 lambda 表达式绑定到此模型，但@Html.DropDownList()不绑定到模型，因此当模型在 HTTPPost 中返回时，选择不存在。
You need to add your Categoryfield to Store.Models.Productand then bind to that list using:
您需要使用以下方法将您的Category字段添加Store.Models.Product到该列表，然后绑定到该列表：
@Html.DropDownListFor(m => m.Category, ViewBag.ListItems)
Then MVC should properly bind your input control to the model.
然后 MVC 应该正确地将您的输入控件绑定到模型。
As an example, this syntax does work:
例如，此语法确实有效：
int[] listItems = {1, 2, 3, 4};
SelectList selectList = new SelectList(listItems);
@Html.DropDownListFor(m => m.CategoryId, selectList);
Note that SelectListinherits from MultiSelectListwhich implements IEnumerable<SelectListItem>.
请注意，SelectList继承自MultiSelectListwhich implements IEnumerable<SelectListItem>。
回答by Mike C.
Follow what Peter G. has mentioned in his answer, but just for informational purposes, you should also be able to change your Post controller to this:
按照 Peter G. 在他的回答中提到的内容进行操作，但仅供参考，您还应该能够将您的 Post 控制器更改为：
[HttpPost]
public ActionResult Create(Product product, int ListItems)
{
}
As Peter has mentioned (once again, use his answer), the problem is that when your form posts, your DropDown list has a name of "ListItems" and there is nothing on your controller for it to bind to.
正如彼得所提到的（再次使用他的回答），问题是当您的表单发布时，您的下拉列表的名称为“ListItems”，并且您的控制器上没有任何东西可以绑定到它。
回答by Philip Tenn
I ended up doing the following:
我最终做了以下事情：
Controller
控制器
...
[HttpPost]
public ActionResult Create(Product product)
{
var categoryId = product.CategoryId;
repository.SaveProduct(product);
return RedirectToAction("Index");
}
...
Razor cshtml View
剃刀 cshtml 视图
...
<p>Category</p>
@Html.DropDownList("CategoryId", (IEnumerable<SelectListItem>) ViewData["ListItems"])
...
It looks ugly and to be honest, I don't fully understand why I was not able to use a lambda expression like Peter suggested, @Html.DropDownListFor(m => m.CategoryId, ViewBag.ListItems).
它看起来很丑，老实说，我不完全理解为什么我不能像 Peter 建议的那样使用 lambda 表达式，@Html.DropDownListFor(m => m.CategoryId, ViewBag.ListItems).
To me, I've "got it to work", but want to understand why, and if there is a more elegant way I can do it.
对我来说，我已经“让它工作了”，但想了解为什么，如果有更优雅的方式我可以做到。
When I typed in @Html.DropDownListFor(m => m.CategoryId, ViewBag.ListItems), IntelliSense would auto-fill m.CategoryId, but then would flag it in red, and I would get runtime error.
当我输入时@Html.DropDownListFor(m => m.CategoryId, ViewBag.ListItems)，IntelliSense 会自动填充m.CategoryId，但随后会将其标记为红色，并且我会收到运行时错误。
