为什么依赖注入在 ASP.net 核心后不起作用？

Question

我在我的控制器中注入了两个类。

在get请求中，当我放一个断点时，我可以看到构造函数中正在检索一个实例。

但是在 post 操作中，实例为空？

这是我的控制器类；

using BethanyPieShop.Models;
using Microsoft.AspNetCore.Mvc;

namespace BethanyPieShop.Controllers
{
    public class OrderController : Controller
    {
        public IOrderRepository _orderRepository { get; set; }
        public ShoppingCart _shoppingCart { get; set; }

        public OrderController(IOrderRepository _orderRepository, ShoppingCart _shoppingCart)
        {
            _orderRepository = _orderRepository;
            _shoppingCart = _shoppingCart;
        }
        public IActionResult Checkout()
        {

            return View();
        }

        [HttpPost]
        public IActionResult Checkout(Order order)
        {
            // Null here _shoppingCart
            var items = _shoppingCart.GetShoppingCartItems();
            _shoppingCart.ShoppingCartItems = items;

            if (_shoppingCart.ShoppingCartItems.Count == 0)
            {
                ModelState.AddModelError("", "Your cart is empty, add some pies first");
            }

            if (ModelState.IsValid)
            {
                _orderRepository.CreateOrder(order);
                _shoppingCart.ClearCart();
                return RedirectToAction("CheckoutComplete");
            }
            return View(order);
        }


        public IActionResult CheckoutComplete()
        {
            ViewBag.CheckoutCompleteMessage = ", thanks for your order. You'll soon enjoy our delicious pies!";
            return View();
        }


    }
}

我在主类中注册了服务：

builder.Services.AddScoped<IOrderRepository, OrderRepository>();
builder.Services.AddScoped<ShoppingCart>();

Answer 1

您正在设置一个具有相同名称的变量。不使用“这个”。陈述。尝试更改以下内容

public OrderController(IOrderRepository _orderRepository, ShoppingCart _shoppingCart)
{
    _orderRepository = _orderRepository;
    _shoppingCart = _shoppingCart;
}

到

public OrderController(IOrderRepository orderRepository, ShoppingCart shoppingCart)
    {
        _orderRepository = orderRepository;
        _shoppingCart = shoppingCart;
    }

Answer 2

所以我认为你应该使用它。像这样：

public OrderController(IOrderRepository _orderRepository, ShoppingCart _shoppingCart)
    {
        this._orderRepository = _orderRepository;
        this._shoppingCart = _shoppingCart;
    }