Question

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

我得到错误：

没有任何论据符合所需的形式参数＆＃39; gItem＆＃39;

＆＃39; Program.GroceryItem.PurchasedItem.FreshItem.FindCost（）＆＃39;隐藏继承的成员＆＃39; Program.GroceryItem.PurchasedItem.FindCost（）＆＃39;。如果想要隐藏，请使用new关键字。

如果项目是新鲜的，我如何才能使用 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

当基类具有带参数的构造函数时，您应该将其称为明确的。它一定是：

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

请参阅：Derived class explicit base constructor call

对于您的第二个问题，PurchasedItem和FreshItem必须从GroceryItem继承并实施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 2

要修复第一个错误，请使用Mazaher Bazari回答

但您的代码仍然无法像您想要的那样工作

尝试像这样修复

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;
    }
}

你应该添加Virtual和Override来覆盖方法，如果不需要新实例作为FreshItem来使用FreshItem FindCost

Answer 3

你这样做：

FreshItem : PurchasedItem

所以你继承了PurchasedItem.FindCost，但你在FindCost中也有FreshItem方法，所以你会收到这个错误，这个错误非常清楚并抱怨你上面做了什么：

Program.GroceryItem.PurchasedItem.FreshItem.FindCost（）＆＃39;隐藏继承的成员＆＃39; Program.GroceryItem.PurchasedItem.FindCost（）＆＃39;。如果想要隐藏，请使用new关键字。

要修复此错误，您可以将PurchasedItem.FindCost声明为虚拟，以便您可以覆盖它：

public virtual double FindCost()

然后在FreshItem中覆盖它：

public override double FindCost()

对于其他错误，请参阅@MazaherBazari的答案。

无法解决方法重载问题

3 个答案: