无法计算方法过载

Question

我试图用FindCost子类中的一个新方法重载PurchasedItem中的FreshItem方法。新的FreshItem FindCost方法使用权重而不是数量来确定成本。

我会犯错误：

不存在与所需的形式参数“gItem”相对应的参数 'Program.GroceryItem.PurchasedItem.FreshItem.FindCost()‘隐藏继承的成员'Program.GroceryItem.PurchasedItem.FindCost()'.如果有意隐藏，请使用新关键字。

如果项目是新的，我如何允许使用FreshItem FindCost方法？

    class Program
    {
        public class GroceryItem
        {
        public string Name;
        public double Price;

        public PurchasedItem pItem
        {
            get;
            set;
        }

        public GroceryItem()
        {
        }

        public GroceryItem(string name, double price)
        {
            this.Name = name;
            this.Price = price;
        }
        public class PurchasedItem
        {
            public int Quantity;
            GroceryItem item;
            public PurchasedItem(GroceryItem gItem)
            {
                item = new GroceryItem(gItem.Name, gItem.Price);
            }

            public double FindCost()
            {
                return item.Price * this.Quantity * 1.10;
            }

            public class FreshItem : PurchasedItem
            {
                public FreshItem() 
                {
                }
                public double weight;

                public double FindCost()
                {
                    return this.item.Price * this.weight;
                }

            }
        }
        public static void Main(string[] args)
        {
            var item1 = new GroceryItem("Lettuce", 2.05);
            item1.pItem = new GroceryItem.PurchasedItem(item1);
            item1.pItem.Quantity = 12;
            double cost1 = item1.pItem.FindCost();


            Console.WriteLine(item1.Name + " " + item1.Price);
            Console.WriteLine(cost1);
        }
    }
}

Answer 1

你这样做：

FreshItem : PurchasedItem

因此，您正在继承PurchasedItem.FindCost，但是在FreshItem中也有FindCost方法，因此您得到了这个错误，这是非常清楚的，并且抱怨您在上面所做的事情：

Program.GroceryItem.PurchasedItem.FreshItem.FindCost()‘隐藏继承的成员'Program.GroceryItem.PurchasedItem.FindCost()'.如果有意隐藏，请使用新关键字。

要修复此错误，可以将PurchasedItem.FindCost声明为虚拟的，这样您就可以重写它：

public virtual double FindCost()

然后在FreshItem中重写它：

public override double FindCost()

有关另一个错误，请参见@MazaherBazari的答复。

Answer 2

当基类有带有参数的构造函数时，您应该将它称为explicity。它必须是：

public FreshItem():base(/*pass paramter*/)
{
}

请参阅：Derived class explicit base constructor call

对于第二个问题，PurchasedItem和FreshItem必须继承GroceryItem并实现FindMethod

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

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

    public abstract double FindCost();
}
public class PurchasedItem: GroceryItem
{
    public int Quantity {set;get;}
    public PurchasedItem(string name, double price, int quntity):base(name, price)
    {
      this.Quantity = quntity;
    }

    public override double FindCost()
    {
        return this.Price * this.Quantity * 1.10;
    }


}
public class FreshItem : GroceryItem
{
    public double Weight {set;get;}

    public FreshItem(string name, double price, int weight) : base(name, price)
    {
        this.Weight= weight;
    }
    public override double FindCost()
    {
        return this.Price * this.Weight;
    }
}


public static void Main(string[] args)
{
    var item1 = new PurchasedItem("Lettuce", 2.05,12);
    double cost1 = item1.FindCost();
}

Answer 3

要修复第一个错误，请使用Mazaher Bazari答案

但是你的代码仍然不能像你想的那样工作

试着像这样修理

class Program
{
    public static void Main(string[] args)
    {
        var item1 = new GroceryItem("Lettuce", 2.05);
        item1.pItem = new FreshItem(item1);
        item1.pItem.Quantity = 12;
        double cost1 = item1.pItem.FindCost();


        Console.WriteLine(item1.Name + " " + item1.Price);
        Console.WriteLine(cost1);
        Console.ReadLine();
    }
}
public class PurchasedItem
{
    public int Quantity;
    protected GroceryItem item;
    public PurchasedItem(GroceryItem gItem)
    {
        item = new GroceryItem(gItem.Name, gItem.Price);
    }

    public virtual double FindCost()
    {
        return item.Price * this.Quantity * 1.10;
    }


}
public class FreshItem : PurchasedItem
{
    public double weight;

    public FreshItem(GroceryItem gItem) : base(gItem)
    {
    }

    public override double FindCost()
    {
        return this.item.Price * this.weight;
    }

}
public class GroceryItem
{
    public string Name;
    public double Price;

    public PurchasedItem pItem
    {
        get;
        set;
    }

    public GroceryItem()
    {
    }

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

如果不需要将Virtual和Override添加到重写方法，则应将新实例作为FreshItem来使用FreshItem FindCost。