使用一个属性为另一个属性创建总计

Question

我是 C# 语言的新手，我试图弄清楚如何让我的 Quantity 属性通过将购买的商品数量乘以 12.35 的商品价格来计算最终价格，只要订购的数量是设置。

我在使用Equals() 方法时也遇到了问题。我正在尝试使用 Equals() 方法根据订单号比较 2 个订单，但我在 Visual Studio 中收到警告说 'Order' overrides Object.Equals(object o) but does not override Object.GetHashCode()。我该如何解决这个问题？

这是我的程序：

using System;

namespace Order 
{
    class Program
    {
        static void Main(string[] args)
        {
            // creating the orders
            Order order1 = new Order(1, "Joe Bob", 2);
            Order order2 = new Order(3, "Sally Bob", 4);
            Order order3 = new Order(1, "Jimmy Bob", 5);
            Console.WriteLine(order1.ToString() + "\n");
            Console.WriteLine(order2.ToString() + "\n");
            Console.WriteLine(order3.ToString() + "\n");

            //checks for duplicates
            CheckDuplicate(order1, order2);
            CheckDuplicate(order2, order3);
            CheckDuplicate(order1, order3);
        }
        // output for duplicates
        public static void CheckDuplicate(Order firstOrder, Order secondOrder)
        {
            if (firstOrder.Equals(secondOrder))
            {
                Console.WriteLine("The two orders are the same!");
            }
            else
            {
                Console.WriteLine("The two orders are not the same!");
            }
        }
    }

    class Order
    {
        // setting properties
        public int OrderNum { get; set; }
        public string CustomerName { get; set; }
        public double Quantity;
        private readonly double Total;
        // total price
        public double GetTotal()
        {
            double itemPrice = 12.35;
            double Total = Quantity * itemPrice;
            return Total;
        }
        // equals to method
        public override bool Equals(Object o)
        {
            bool isEqual = true;
            if (this.GetType() != o.GetType())
                isEqual = false;
            else
            {
                Order temp = (Order)o;
                if (OrderNum == temp.OrderNum)
                    isEqual = true;
                else
                    isEqual = false;
            }
            return isEqual;
        }
        // default constructor
        public Order(int OrderNum, string CustomerName, double Quantity)
        {
            this.OrderNum = OrderNum;
            this.CustomerName = CustomerName;
            this.Quantity = Quantity;
        }
        // returns final output
        public override string ToString()
        {
            return ("Order Number       : " + OrderNum) + "\n" + ("Customer name      : " + CustomerName) + "\n" + ("Quantity Ordered   : " + Quantity) + "\n" + ("Totatl Price       : " + Total);
        }
    }
}

Answer 1

该属性就像一个函数一样工作。您可以将Total 声明为只读属性，并声明一个执行乘法运算的getter。

public double Quantity;
public double Total {
    get {
        const double itemPrice = 12.35;
        return Quantity * itemPrice;
    }
}

重写 Object.GetHashCode() 很容易。如果两个项目相同，您应该创建一个返回相同值的函数。 因为您使用 OrderNum 作为识别订单的唯一方法。只需返回它即可完成工作。

public override int GetHashCode() {
    return this.OrderNum;
}

Answer 2

我想这就是你要找的东西：

public sealed class Order : IEquatable<Order>
{
    // Properties & Fields
    public int OrderNum { get; set; }
    public string CustomerName { get; set; }
    public double Quantity { get; set; }
    public double ItemPrice { get; set; } 
    public double TotalPrice => Quantity*ItemPrice;

    // Constructor
    public Order(int orderNum, string customerName, double quantity, double itemPrice = 12.35)
    {
        this.OrderNum = orderNum;
        this.CustomerName = customerName;
        this.Quantity = quantity;
        this.ItemPrice = itemPrice;
    }

    // Equality

    /// <summary>
    /// Equality overrides from <see cref="System.Object"/>
    /// </summary>
    /// <param name="obj">The object to compare this with</param>
    /// <returns>False if object is a different type, otherwise it calls <code>Equals(Order)</code></returns>
    public override bool Equals(object obj)
    {
        if (obj is Order order)
        {
            // Uses pattern matching when `obj` is of type `Order`
            return Equals(order);
        }
        return false;
    }

    /// <summary>
    /// Checks for equality among <see cref="Order"/> classes
    /// </summary>
    /// <param name="other">The other <see cref="Order"/> to compare it to</param>
    /// <returns>True if equal</returns>
    public bool Equals(Order other)
    {
        return OrderNum.Equals(other?.OrderNum);
    }

    /// <summary>
    /// Calculates the hash code for the <see cref="Order"/>
    /// </summary>
    /// <returns>The int hash value</returns>
    public override int GetHashCode()
    {
        return (17+23*OrderNum.GetHashCode());
    }

    // Display
    public override string ToString()
    {
        return string.Join(Environment.NewLine, new string[] {
            $"Order Number       : {OrderNum}",
            $"Customer name      : {CustomerName}",
            $"Item Price         : {ItemPrice:F2}",
            $"Quantity Ordered   : {Quantity:F3}",
            $"Total Price        : {TotalPrice:F2}",
            Environment.NewLine,
        });
    }
}

按如下方式使用：

class Program
{
    static void Main(string[] args)
    {
        // creating the orders
        List<Order> orders = new List<Order>();
        orders.Add(new Order(1, "Joe Bob", 2));
        orders.Add(new Order(3, "Sally Bob", 4));
        orders.Add(new Order(1, "Jimmy Bob", 5));

        Console.WriteLine("List of all orders.");
        foreach (var order in orders)
        {
            Console.WriteLine(order);
        }

        Console.WriteLine("Found the following duplicates.");
        // Code taken from: https://stackoverflow.com/a/18547390/380384
        // It uses the `IEquatable<>` interface to check for duplicates.
        foreach (var item in orders.GroupBy((order) => order).Where(grp => grp.Count()>1))
        {
            Console.WriteLine(item.Key);
        }
    }
}

有输出

List of all orders.
Order Number       : 1
Customer name      : Joe Bob
Item Price         : 12.35
Quantity Ordered   : 2.000
Total Price        : 24.70


Order Number       : 3
Customer name      : Sally Bob
Item Price         : 12.35
Quantity Ordered   : 4.000
Total Price        : 49.40


Order Number       : 1
Customer name      : Jimmy Bob
Item Price         : 12.35
Quantity Ordered   : 5.000
Total Price        : 61.75


Found the following duplicates.
Order Number       : 1
Customer name      : Joe Bob
Item Price         : 12.35
Quantity Ordered   : 2.000
Total Price        : 24.70