创建继承通用默认参数的Collection类

Question

I would like to create a C# class outside a repository, which inherits all the default generic methods (Add, Remove All, etc). This following code works. My goal is to move List ShoppingCart outside the repository.

public class CartLine
{
    public int CartLineId { get; set; }
    public int ProductId { get; set; }
    public int Quantity { get; set; }
}

Following Code Works:

 public class ShoppingCartRepository
    {

        private List<CartLine> ShoppingCart = new List<CartLine>();


        public IEnumerable GetShoppingCart()
        {
            return ShoppingCart.ToList();
        }

        public virtual void AddItem(int productid, int quantity)
        {
            ShoppingCart.Add(new CartLine { ProductId = productid, Quantity = quantity });
        }

        public virtual void RemoveItem(int cartlineid)
        {
            ShoppingCart.RemoveAll(l => l.CartLineId == cartlineid);
        }

This Code Does not work: "Error: Shopping Cart does not contain definition for ToList. "

public class ShoppingCart : List<ShoppingCart>
{
    public ShoppingCart()
    {
        List<CartLine> ShoppingCart = new List<CartLine>();
    }
}


public class ShoppingCartRepository
{

    //private List<CartLine> ShoppingCart = new List<CartLine>();


    public IEnumerable GetShoppingCart()
    {
        return ShoppingCart.ToList();
    }

    public virtual void AddItem(int productid, int quantity)
    {
        ShoppingCart.Add(new CartLine { ProductId = productid, Quantity = quantity });
    }

    public virtual void RemoveItem(int cartlineid)
    {
        ShoppingCart.RemoveAll(l => l.CartLineId == cartlineid);
    }

}

Answer 1

Maybe this would help you.

public class CartLine
{
        public int CartLineId { get; set; }
        public int ProductId { get; set; }
        public int Quantity { get; set; }
}

    public class ShoppingCart : List<CartLine>
    {
        public ShoppingCart()
        {
        }

    }

    public class ShoppingCartRepository
    {

        private ShoppingCart ShoppingCart = new ShoppingCart();

        public IEnumerable GetShoppingCart()
        {
            return ShoppingCart.ToList();
        }

        public virtual void AddItem(int productid, int quantity)
        {
            ShoppingCart.Add(new CartLine
            {
                ProductId = productid,
                Quantity = quantity
            });
        }

        public virtual void RemoveItem(int cartlineid)
        {
            ShoppingCart.RemoveAll(l => l.CartLineId == cartlineid);
        }

    }

I change the class to make it generic. The Problem I think is, that you make your make a generic list of ShoppingCart but you want to add CartLine .

I hope this help you.

Answer 2

I am not sure why are you trying to move Shopping cart outside, but there are many problems with the code

1. You will need to define List<CartLine> ShoppingCart property in the class ShoppingCartRepository . Right now you are creating it inside constructor. That will not make ShoppingCart property/field of the class.
2. As mentioned below in the comments, ToList() is not part of the List . So you will not be able to use it unless you explicitly define it. But not sure why you need to call ToList() on a List element.
3. Also, you shouldn't inherit from List<ShoppingCart> , instead use interface - IList<T> . That will help you with mocking/testing.

More importantly I don't see any value add in what you are trying to do. If you can provide more details around that, may be I can provide more details.