Why dependency injection is not working in post ASP.net core?

Question

I am injecting two classes in my controller.

In the get request, when I put a break point, I can see there is an instance being retrieved in the constructor .

However in the post action, the instance is null ?

here is my controller class;

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();
        }


    }
}

I registered the services in the main class:

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

Your parameters have the same name as the fields so the hide them. I suspect you already get compiler warnings about this. Your code is assigning the parameter value to the parameter itself — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Feb 23, 2022 at 13:29
Don't use leading underscores in parameter names. By convention a leading underscore is only used in private fields. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Feb 23, 2022 at 13:32

Rule · Accepted Answer · 2022-02-23 13:26:10Z

5

You are setting a variable with the same name. Without using a 'this.' statement. Try changing the following from

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

to

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

answered Feb 23, 2022 at 13:26

Rule

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1 Comment

Panagiotis Kanavos Over a year ago

It's worth explaining why the problem occurred in the first place - the parameters are defined in the constructor's scope so they hide the fields with the same name defined in an outer scope. I think the compiler already generates a warning for this. Resharper certainly does

Jorne Schuurmans · Accepted Answer · 2022-02-23 13:26:10Z

1

So I think you should use this. Like this:

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

answered Feb 23, 2022 at 13:26

Jorne Schuurmans

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4 Comments

Panagiotis Kanavos Over a year ago

The real solution would be to not use an underscore in a public member parameter

Jorne Schuurmans Over a year ago

True, I personly would make those variables private readonly.

user123456 Over a year ago

@PanagiotisKanavos Thanks i wll change it

user123456 Over a year ago

@JorneSchuurmans thanks I wll change it

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