在MVC 5中填充下拉列表

本文关键字：填充 下拉列表 MVC | 更新日期: 2023-09-27 18:04:44

这是我的AddNewProductViewModel

的代码
using AccessorizeForLess.Data;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Web;
namespace AccessorizeForLess.ViewModels
{
    public class AddNewProductViewModel
    {
        public string Name { get; set; }
        [DataType(DataType.MultilineText)]
        public string Description { get; set; }
        public decimal Price { get; set; }
        public string AltText { get; set; }
        public int Quantity { get; set; }
        public string ImagePath { get; set; }
        public HttpPostedFileBase Image { get; set; }
        public List<ProductCategory> Category { get; set; }
    }
}

这是我的在控制器中创建方法

[HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<ActionResult> Create(AddNewProductViewModel model)
        {
            ProductImageViewModel image = new ProductImageViewModel() { ImagePath = "/Content/ProductImages/" + model.Image.FileName, AltText = model.AltText };
            ProductImage newImage = new ProductImage() { ImagePath = image.ImagePath, AltText = image.AltText };
            entities.ProductImages.Add(newImage);
            await entities.SaveChangesAsync();
            int ImageId = newImage.ProductImageId;
            Product product = new Product()
            {
                ProductImageId = ImageId,
                ProductName = model.Name,
                ProductDescription = model.Description,
                ProductPrice = model.Price,
                Quantity = model.Quantity
                CategoryID = model.
            };
            string file = model.Image.FileName;
            string path = Server.MapPath(@"~/Content/ProductImages");
            string fullPath = path + @"'" + file;
            try
            {
                model.Image.SaveAs(path + @"'" + file);
                if (ModelState.IsValid)
                {
                    entities.Products.Add(product);
                    await entities.SaveChangesAsync();
                    return RedirectToAction("Create");
                }
            }
            catch (Exception ex)
            {
                ViewBag.Message = ex.ToString();
            }
           //ViewBag.ProductImageId = new SelectList(entities.ProductImages, "ProductImageId", "ImagePath", product.ProductImageId);
            return View("Create");
        }

现在我要在视图中填充下拉列表

<div class="form-group">
            @Html.LabelFor(model => model.Category, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(model => model.Category.Id, new SelectList(Model.Category,"Value","Text"), "- Please Select -")
                @Html.ValidationMessageFor(model => model.Category)
            </div>
        </div>

我得到的错误是:

CS0411:方法的类型参数"System.Web.Mvc.Html.SelectExtensions.DropDownListFor (System.Web.Mvc.HtmlHelper,System.Linq.Expressions.Expression>,System.Collections.Generic.IEnumerable,Object)'不能从用法中推断出来。尝试指定类型论点明确。

编辑

这是新的AddNewProductViewModel

using AccessorizeForLess.Data;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Web;
namespace AccessorizeForLess.ViewModels
{
    public class AddNewProductViewModel
    {
        public string Name { get; set; }
        [DataType(DataType.MultilineText)]
        public string Description { get; set; }
        public decimal Price { get; set; }
        public string AltText { get; set; }
        public int Quantity { get; set; }
        public string ImagePath { get; set; }
        public HttpPostedFileBase Image { get; set; }
        public ProductCategory Category { get; set; }
        public int SelectedCategoryId { get; set; }
        public List<ProductCategory> Categories { get; set; }
}
}

和我更新的下拉列表

<div class="form-group">
            @Html.LabelFor(model => model.Category, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(model => model.SelectedCategoryId,
                 new SelectList(Model.Categories, "CategoryId", "CategoryName"), "- Please Select -")
                @Html.ValidationMessageFor(model => model.Category)
            </div>
        </div>

现在我得到一个NullReferenceException在这行

@Html.DropDownListFor(model => model.SelectedCategoryId,

给出我的代码，有人可以告诉我我在这里做错了什么，我一直在挣扎，因为昨晚

在MVC 5中填充下拉列表

我解决了这个问题(感谢每个人的提示)。这是写给那些可能和我一样有问题的人的。

我改变了我的Create方法，看起来像这样:

// GET: /Products/Create
public ActionResult Create()
{
    var p = new AddNewProductViewModel();
    p.Categories = entities.ProductCategories.ToList();
    return View(p);
}

我的AddNewProductViewModel看起来像这样:

using AccessorizeForLess.Data;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Web;
namespace AccessorizeForLess.ViewModels
{
    public class AddNewProductViewModel
    {
        public string Name { get; set; }
        [DataType(DataType.MultilineText)]
        public string Description { get; set; }
        public decimal Price { get; set; }
        public string AltText { get; set; }
        public int Quantity { get; set; }
        public HttpPostedFileBase Image { get; set; }
        public int SelectedCategoryId {get;set;}
        public List<ProductCategory> Categories { get; set; }
        public ProductCategory Category { get; set; }
    }
}

in my view:

<div class="form-group">
    @Html.LabelFor(model => model.SelectedCategoryId, "Category",new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownListFor(model => model.SelectedCategoryId, new SelectList(Model.Categories, "CategoryId", "CategoryName"), "- Please Select -")
        @Html.ValidationMessageFor(model => model.SelectedCategoryId)
    </div>
</div>

谢谢大家的帮助

首先，我会改变你的ViewModel包括一个SelectedCategoryId，我会改变你的选项为Categories。

没有看到您的get的代码，我假设ProductCategory是如下所示:

public class ProductCategory {
  public int Id {get;set;}
  public string Name { get;set;}
}

你的剃刀标价会变成:

<div class="form-group">
     @Html.LabelFor(model => model.Categories, new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownListFor(model => model.SelectedCategoryId, 
            new SelectList(Model.Categories, "Id", "Name"), "- Please Select -")
            @Html.ValidationMessageFor(model => model.Categories)
        </div>
</div>

第一个参数是选择的类别，您的选项是从Categories填充的。

WorkingFiddle

使用控制器构建列表，然后从视图调用列表。

控制器: 

public static List<SelectListItem> GetDropDown()
    {
        List<SelectListItem> ls = new List<SelectListItem>();
        lm = (call database);
        foreach (var temp in lm)
        {
            ls.Add(new SelectListItem() { Text = temp.name, Value = temp.id });
        }
        return ls;
    }
调用下拉列表: 
@Html.DropDownListFor(x => x.Field, PathToController.GetDropDown())
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