MVC模型返回空值

Question

Error Error I am quite new to MVC and this is my first question in stackoverflow, so please bear with me. I have been getting ArgumentNullException from my Customer Model. The exact same code seems to be working in VS 2013 as shown in one of my training videos but does not work in my VS 2019. Can anyone please suggest on how to fix this error?

Below is my code for the CustomersController

using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Web.Mvc;
using Vidly.Models;

namespace Vidly.Controllers
{
    public class CustomersController : Controller
    {

        private ApplicationDbContext _context;

        public CustomersController()
        {
            _context = new ApplicationDbContext();
        }

        protected override void Dispose(bool disposing)
        {
            _context.Dispose();
        }
        public ViewResult Index()
        {
            /* Eager Loading */
            var customers = _context.Customers.Include(c => c.MembershipType).ToList();   

            return View(customers);
        }

        public ActionResult Details(int id)
        {
            var customer = _context.Customers.SingleOrDefault(c => c.Id == id);

            if (customer == null)
                return HttpNotFound();

            return View(customer);
        }

        
    }
}

And this is my Customers View.

@model IEnumerable<Vidly.Models.Customer>


@{
    ViewBag.Title = "Customers";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Customers</h2>
@if (!Model.Any())
{
    <p>We don't have any customers yet.</p>
}
else
{
    <table class="table table-bordered table-hover">
        <thead>
            <tr>
                <th>Customer</th>
                <th>Membership Type</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var customer in Model)
            {
            <tr>
                <td>@Html.ActionLink(customer.Name, "Details", "Customers", new { id = customer.Id }, null)</td>
                <td>@customer.MembershipType.Name</td>

            </tr>
            }
        </tbody>
    </table>
}

Answer 1

I have checked and found no problem.

In Controller:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using Vidly.Data;
using Vidly.Models;

namespace Vidly.Controllers
{
    public class CustomersController : Controller
    {
        private readonly ApplicationDbContext _context;

        public CustomersController(ApplicationDbContext context)
        {
            _context = context;
        }

        // GET: Customers
        //public async Task<IActionResult> Index()
        //{
        //    return View(await _context.Customer.ToListAsync());
        //}

        public ViewResult Index()
        {
            /* Eager Loading */
            var customers = _context.Customers.Include(c => c.MembershipType).ToList();

            return View(customers);
        }

        // GET: Customers/Details/5
        public async Task<IActionResult> Details(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var customer = await _context.Customers
                .FirstOrDefaultAsync(m => m.Id == id);
            if (customer == null)
            {
                return NotFound();
            }

            return View(customer);
        }

        // GET: Customers/Create
        public IActionResult Create()
        {
            return View();
        }

        // POST: Customers/Create
        // To protect from overposting attacks, enable the specific properties you want to bind to, for 
        // more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("Id,Name,MembershipType")] Customer customer)
        {
            if (ModelState.IsValid)
            {
                _context.Add(customer);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            return View(customer);
        }

        // GET: Customers/Edit/5
        public async Task<IActionResult> Edit(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var customer = await _context.Customers.FindAsync(id);
            if (customer == null)
            {
                return NotFound();
            }
            return View(customer);
        }

        // POST: Customers/Edit/5
        // To protect from overposting attacks, enable the specific properties you want to bind to, for 
        // more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Edit(int id, [Bind("Id,Name,MembershipType")] Customer customer)
        {
            if (id != customer.Id)
            {
                return NotFound();
            }

            if (ModelState.IsValid)
            {
                try
                {
                    _context.Update(customer);
                    await _context.SaveChangesAsync();
                }
                catch (DbUpdateConcurrencyException)
                {
                    if (!CustomerExists(customer.Id))
                    {
                        return NotFound();
                    }
                    else
                    {
                        throw;
                    }
                }
                return RedirectToAction(nameof(Index));
            }
            return View(customer);
        }

        // GET: Customers/Delete/5
        public async Task<IActionResult> Delete(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var customer = await _context.Customers
                .FirstOrDefaultAsync(m => m.Id == id);
            if (customer == null)
            {
                return NotFound();
            }

            return View(customer);
        }

        // POST: Customers/Delete/5
        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            var customer = await _context.Customers.FindAsync(id);
            _context.Customers.Remove(customer);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }

        private bool CustomerExists(int id)
        {
            return _context.Customers.Any(e => e.Id == id);
        }
    }
}

In View:

@model IEnumerable<Vidly.Models.Customer>


@{
    ViewBag.Title = "Customers";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Customers</h2>
@if (!Model.Any())
{
    <p>We don't have any customers yet.</p>
}
else
{
    <table class="table table-bordered table-hover">
        <thead>
            <tr>
                <th>Customer</th>
                <th>Membership Type</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var customer in Model)
            {
                <tr>
                    <td>@Html.ActionLink(customer.Name, "Details", "Customers", new { id = customer.Id }, null)</td>
                    <td>@customer.MembershipType</td>

                </tr>
            }
        </tbody>
    </table>
}

In Model

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Threading.Tasks;

namespace Vidly.Models
{
    public class Customer
    {
        [Key]
        public int Id { get; set; }
        public string Name { get; set; }
        public MembershipType MembershipType { get; set; }
    }
}