Question

我是C＃的新手，请原谅我所知的差距。在我的代码中，我有两种类型的食物Fresh和Regular。确定成本时，新鲜项目使用与常规不同的FindCost方法。

我无法解决如何为Fresh Items调用FindCost（）方法。

我想我需要以某种方式使用base关键字：

namespace Groceries
{
    class Program
    {
        static void Main(string[] args)
        {


            PurchasedItem CheckoutItem4 = new FreshItem();
            CheckoutItem4.Name = "Rump Steak";
            CheckoutItem4.Condition = "Fresh";
            CheckoutItem4.Price = 11.99;
            CheckoutItem4.Weight = .8;


            ArrayList invoiceArray = new ArrayList();
            invoiceArray.Add(CheckoutItem1);


            foreach (PurchasedItem checkoutItem in invoiceArray)
            {

                Console.WriteLine($"Quantity: {checkoutItem.Quantity} Weight: {checkoutItem.Weight}kg ");


            }

            Console.ReadLine();
        }
    }
    public class GroceryItem
    {

        public string Name { get; set; }
        public string Condition { get; set; }
        public double Price { get; set; }


        public GroceryItem()
        {
        }

        public GroceryItem(string name, double price)
        {
            this.Name = name;
            this.Price = price;
        }

        public static void Invoice()
        {
            Console.WriteLine();
        }

    }

    public class PurchasedItem : GroceryItem 
    {
        public int Quantity { get; set; }
        public double Weight { get; internal set; }

        public virtual double FindCost()
        {

            double cost = Quantity * Price * 1.1; //1.1 is GST
            return cost;
        }
    }

    public class FreshItem : PurchasedItem
    {
        public new double Weight { get; set; } //kg

        public override double FindCost()
        {

            double cost = Weight * Price;
            return cost;
        }
    }

}

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Answer 1

您当前的代码正确地调用了正确的FindCost()方法，但您已经以糟糕的方式定义了类，并且使用new关键字隐藏可能会使其调用错误的方法。

您应该GroceryItem abstract并让您的两个类直接从此继承。然后GroceryItem可以使用abstract FindCost()方法。此外，如果您隐藏了new的方法，那么您可能做错了什么。您应该发现这在调用FindCost()时消除了所有不确定性。

另外，您应该使用decimal而不是double进行财务计算，因为double并不总是准确地代表货币价值。

以下是改进的课程：

void Main()
{
    List<GroceryItem> invoiceArray = new List<GroceryItem>()
    {
        new FreshItem() { Name = "Rump Steak", Price = 11.99m, Weight = 0.8 },
        new PurchasedItem() { Name = "Cream", Price = 2.2m, Quantity = 1, Weight = 0.6 },
    };

    foreach (GroceryItem checkoutItem in invoiceArray)
    {
        if (checkoutItem is PurchasedItem purchasedItem)
        {
            Console.WriteLine($"Condition: {checkoutItem.Condition}; Quantity: {purchasedItem.Quantity}; Weight: {checkoutItem.Weight}kg");
        }
        else
        {
            Console.WriteLine($"Condition: {checkoutItem.Condition}; Weight: {checkoutItem.Weight}kg");
        }
    }

    Console.ReadLine();
}

public abstract class GroceryItem
{
    public string Name { get; set; }
    public abstract string Condition { get; }
    public double Weight { get; set; }
    public decimal Price { get; set; }

    public GroceryItem() { }

    public GroceryItem(string name, decimal price)
    {
        this.Name = name;
        this.Price = price;
    }

    public abstract decimal FindCost();
}

public class PurchasedItem : GroceryItem
{
    public int Quantity { get; set; }

    public override string Condition { get { return "Regular"; } }

    public override decimal FindCost()
    {
        decimal cost = Quantity * Price * 1.1m; //1.1m is GST
        return cost;
    }
}

public class FreshItem : GroceryItem
{
    public override string Condition { get { return "Fresh"; } }

    public override decimal FindCost()
    {
        decimal cost = (decimal)Weight * Price;
        return cost;
    }
}

Answer 2

使用PurchasedItem类型的引用设置Weight时： CheckoutItem4.Weight = .8; 您设置在PurchasedItem类中声明的字段Weight，但FindCost方法使用未初始化的类FreshItem中定义的字段Weight。所以，只需删除de line： public new double Weight {get;组; } // kg 。您无需重新定义此字段。

C＃ - 调用覆盖方法

2 个答案: