在渲染部分视图的下拉列表时，对象引用未设置为对象的实例

Question

我正在尝试使用mvc 5和EF6从数据库加载下拉列表。当我执行应用程序

时，我不断收到错误“对象引用未设置为对象的实例”错误

这是我的模特：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using dtPerson_v10_p1;
using Nevron.Chart;

namespace ds_iDMS.Models.Deals
{
    public class WorksheetAfterMarketViewModel
    {
        [Display(Name = @"Integrated Product:")]
        public string integratedProduct { get; set; }

        public List<SelectListItem> IntProducts { get; set; }
        public List<SelectListItem> CompanyNames { get; set; }
        public List<ProductCategoryItem> ProductCategories { get; set; }

        public WorksheetAfterMarketViewModel()
        {
            IntProducts = new List<SelectListItem>();
            CompanyNames = new List<SelectListItem>();
        }


    }

    public class ProductCategoryItem
    {
        [Display(Name = @"Price")]
        [DisplayFormat(DataFormatString = "{0:C0}")]
        [DataType(DataType.Currency)]
        public float Price { get; set; }

        [Display(Name = @"Cost")]
        [DisplayFormat(DataFormatString = "{0:C0}")]
        [DataType(DataType.Currency)]
        public float Cost { get; set; }

        [Display(Name = @"Company")]
        public string Company { get; set; }

        [Display(Name = @"Code")]
        public string Code { get; set; }

        [Display(Name = @"Description")]
        public string Description { get; set; }

        [Display(Name = @"Mileage")]
        public string Mileage { get; set; }

        [Display(Name = @"Term")]
        public string Term { get; set; }

        public ProductCategoryItem()
        {
            Price = 0;
            Cost = 0;
            Company = "";
            Code = "";
            Description = "";
            Mileage = "";
            Term = "";
        }



    }

}

以下是部分视图：

    @model ds_iDMS.Models.Deals.WorksheetAfterMarketViewModel

<div class="table_border_detail">
    <h4 class="fex_section_header">Products</h4>

    @using (Html.DSInputGroupRow(numberOfInputs: ExtensionMethods.NumberOfInputs.OneIput))
    {
        @Html.DSSelectFor(m => m.integratedProduct, new SelectList(Model.IntProducts, "Value", "Text", Model.integratedProduct))
    }

    @for (int i = 0; i < 10; i++)
    {
        using (Html.DSInputGroupRow(numberOfInputs: ExtensionMethods.NumberOfInputs.SevenInputs))
        {
           @Html.DSInputFor(m => m.ProductCategories[i].Price)
           @Html.DSInputFor(m => m.ProductCategories[i].Cost)
           @Html.DSSelectFor(m => m.ProductCategories[i].Company, new SelectList(Model.CompanyNames, "Value", "Text", Model.ProductCategories[i].Company))
           @Html.DSInputFor(m => m.ProductCategories[i].Code)
           @Html.DSInputFor(m => m.ProductCategories[i].Description)
           @Html.DSInputFor(m => m.ProductCategories[i].Mileage)
           @Html.DSInputFor(m => m.ProductCategories[i].Term)
        }
    }
</div>

以下是我们用于控制器的服务：

@model ds_iDMS.Models.Deals.WorksheetAfterMarketViewModel

<div class="table_border_detail">
    <h4 class="fex_section_header">Products</h4>

    @using (Html.DSInputGroupRow(numberOfInputs: ExtensionMethods.NumberOfInputs.OneIput))
    {
        @Html.DSSelectFor(m => m.integratedProduct, new SelectList(Model.IntProducts, "Value", "Text", Model.integratedProduct))
    }

    @for (int i = 0; i < 10; i++)
    {
        using (Html.DSInputGroupRow(numberOfInputs: ExtensionMethods.NumberOfInputs.SevenInputs))
        {
           @Html.DSInputFor(m => m.ProductCategories[i].Price)
           @Html.DSInputFor(m => m.ProductCategories[i].Cost)
           @Html.DSSelectFor(m => m.ProductCategories[i].Company, new SelectList(Model.CompanyNames, "Value", "Text", Model.ProductCategories[i].Company))
           @Html.DSInputFor(m => m.ProductCategories[i].Code)
           @Html.DSInputFor(m => m.ProductCategories[i].Description)
           @Html.DSInputFor(m => m.ProductCategories[i].Mileage)
           @Html.DSInputFor(m => m.ProductCategories[i].Term)
        }
    }
</div>

这是抛出错误时突出显示的行

@Html.DSSelectFor(m => m.ProductCategories[i].Company, new SelectList(Model.CompanyNames, "Value", "Text", Model.ProductCategories[i].Company))

我很丢失，不知道如何处理这个错误。如果您需要别的东西请告诉我