C＃ - 调用覆盖方法

Question

我是C＃的新手，所以请原谅我的知识空白。在我的代码中，我有两种新鲜和常规的食物。 确定成本时新鲜料品使用与普通不同的FindCost方法。

我在解决如何为Fresh项目调用FindCost（）方法时遇到问题。

我想我需要使用基本关键字莫名其妙S：

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

您当前的代码是否正确调用正确的FindCost()方法，但你在定义了类不好的方法，并与new关键字隐藏可以使它调用错误的方法。

您应该制作GroceryItemabstract并让您的两个类直接继承此类。然后GroceryItem可以有一个abstractFindCost()方法。另外，如果你隐藏了一个方法new那么你可能做错了什么。你应该发现，这呼叫FindCost()时消除了所有的不确定性。

此外，您应该使用decimal而不是double进行财务计算，因为double并不总是精确地表示货币值。

下面是改进的类：

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

当设置重量连类型PurchasedItem的参考： CheckoutItem4.Weight = 0.8; 您设置了在类PurchasedItem中声明的字段Weight，但方法FindCost使用FreshItem类中定义的字段Weight，该字段未初始化。所以，只需删除德行：public new double Weight {get;组; } // kg。您不需要重新定义此字段。