子类看不到父方法

如何解决子类看不到父方法

我必须进行一次测试，我主要通过了MCQ部分，但是我的编码部分无法正常工作，并且由于我们的讲师不太热衷于提供反馈，因此我希望了解自己的错误并从中进行改进。解释性注释在代码中。

在Program类中，我遇到两个错误（从技术上讲三个，但一个与另一个相同）。在带有“ Console.WriteLine（“ Commission is：”，item.CalculateComission）;“的行中我得到： “ CS1061'double'不包含'CalculateComission'的定义，并且找不到扩展方法'CalculateComission'接受类型为'double'的第一个参数（您是否缺少using指令或程序集引用？）”

在“ GetCheapestResidance（apartments）;”行中我得到： “ CS1503：参数1：无法从“ System.Collections.Generic.List ”转换为“ System.Collections.Generic.List ”

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Test2
{
    abstract class Residence
    {
        //properties Bedrooms,Bathrooms,Price
        public int Bedrooms { get; set; }

        public int Bathrooms { get; set; }

        public double Price { get; set; }

        //A no-argument constructor that creates a default Residence
        public Residence() 
        {
        
        }

        //A constructor that creates a Residence with the specified bedrooms,bathrooms,price
        public Residence(int bedrooms,int bathrooms,double price) 
        {
            Bedrooms = bedrooms;
            Bathrooms = bathrooms;
            Price = price;
        }

        //CalculateCommission() (public): abstract method with return type: double
        public abstract double CalculateCommission();
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace Test2
{
    class Apartment : Residence
    {
        //Properties: Unit and Floor. Both are integer type 
        public int Unit { get; set; }

        public int Floor { get; set; }

        //A no-argument constructor
        public Apartment() { }

        //A constructor that creates a apartment object with the specified bedrooms,price,Unit and Floor
        public Apartment(int unit,int floor,int bedrooms,double price) : base(bedrooms,price)
        {
            Unit = unit;
            Floor = floor;
        }

        //Override CalculateCommission() method. The commission rate for an apartment is set up at 3%
        public override double CalculateCommission()
        {
            return Price * 0.03;
        }

        //toString() that returns the information about the current object
        public override string ToString()
        {
            return $" Bedrooms: {Bedrooms}\n" +
                $"Bathrooms: {Bathrooms}\n" +
                $"Floor: {Floor}\n" +
                $"Unit: {Unit}\n" +
                $"Price: {Price}";
        }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace Test2
{
    class House : Residence
    {
        //Propeties:  Stories and Basement.Stories is integer type,Basement is Boolean type,//indicating whether the house has basement
        public int Stories { get; set; }

        public bool Basement { get; set; }

        //A no-arg constructor
        public House() { }

        //A constructor that creates a house object with the specified bedrooms,//bathrooms,stories,basement

        public House(int stories,bool basement,price)
        {
            Stories = stories;
            Basement = basement;
        }

        //toString() that returns the information about the apartment
        public override string ToString()
        {
            return $" Bedrooms: {Bedrooms}\n" +
                $"Bathrooms: {Bathrooms}\n" +
                $"Stories: {Stories}\n" +
                $"Basement: {Basement}\n" +
                $"Price: {Price}";
        }

        //Override CalculateCommission() method. The commission rate for a house is set up at 3.5%
        public override double CalculateCommission()
        {
            return Price * 0.035;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;

namespace Test2
{
    class Program
    {

        public static void GetCheapestResidance(List<Residence> list)
        {
            //finds the cheapest residence in the list (either in the houses list or apartments list ) 
            //depending on the parameter that you will pass. 
            var item = list.Min(x => x.Price);

            //then display the information about the cheapest residence using ToString()
            Console.WriteLine("The cheapest is: ",item.ToString());

            //and display the commission
            Console.WriteLine("Commission is: ",item.CalculateComission);
        }

        static void Main(string[] args)
        {
            List<House> houses = new List<House>();
            List<Apartment> apartments = new List<Apartment>();

            //Create three house objects  and three apartment object with data of your choice. 
            //Then add them to the the above lists.

            Residence ap1 = new Apartment(101,1,1100);
            Residence ap2 = new Apartment(102,2,1500);
            Residence ap3 = new Apartment(103,3,1900);

            Residence hs1 = new House(1,false,1500);
            Residence hs2 = new House(1,true,1900);
            Residence hs3 = new House(2,4,2300);
                        
            apartments.Add((Apartment)ap1);
            apartments.Add((Apartment)ap2);
            apartments.Add((Apartment)ap3);

            houses.Add((House)hs1);
            houses.Add((House)hs2);
            houses.Add((House)hs3);

            //Invoke GetCheapestResidance method by passing either houses list OR department list

            GetCheapestResidance(apartments);

            GetCheapestResidance(houses);

            Console.ReadKey();
        }
    }
}

解决方法

要回答第一个问题，请注意错误的措辞：“ CS1061'double'不包含'CalculateComission'的定义”。该错误表明您有一个类型为double的变量，您正在尝试对其调用CalculateComission（）。错误发生在这里：

var item = list.Min(x => x.Price);
Console.WriteLine("Commission is: ",item.CalculateComission);

请注意，您没有指定item的类型，而只是说了var item。发生错误是因为Min函数返回给它的最小值。在这种情况下，您要给该功能提供价格清单。因此，item变量实际上是double类型，而不是Residence类型。因此，您正在尝试拨打电话号码CalculateCommission()，而不是在住宅电话上拨打电话。

要回答第二个问题，您不能仅将List<Apartment>用作List<Residence>。请注意以下固定代码：

//a list of residences instead of a list of apartments
List<Residence> apartments = new List<Residence>(); 

//Because Apartment is a Residence,you can make these variables Apartment or Residence
Apartment ap1 = new Apartment(101,1,1100); 
Residence ap2 = new Apartment(102,2,1500);
Apartment ap3 = new Apartment(103,3,1900);

apartments.Add(ap1);
apartments.Add(ap2);
apartments.Add(ap3);

//This time the function call is valid because GetCheapestResidance() expects a                 
List<Residence>
//and that is what we are passing in
GetCheapestResidance(apartments);

由于您的Apartment类扩展了Residence，因此您可以简单地创建一个List<Residence>作为您的公寓列表，并像往常一样将公寓添加到其中。这应该解决将List<Apartment>传递到期望List<Residence>的函数中的问题。

所有好的问题。

我一次要经历一个：

双精度型错误是因为您的var item = list.Min(...在遍历列表后返回了最小值。它返回找到的价格的最小值，而不是拥有该值的对象的价格。

要解决此问题，您可以使用.Aggregate函数。这有点复杂，所以我建议您看一下这篇文章以获取更多详细信息：How to use LINQ to select object with minimum or maximum property value 。您可以执行此操作的另一种方法是使用简单的for或foreach循环，并在迭代过程中跟踪最小值及其所有者。

此方法GetCheapestResidence抱怨的原因是，它需要一个Residences列表，而您提供一个Apartments列表。不幸的是，您不能将这些列表相互区分，我认为这是列表的限制（如果有人知道为什么，请在下面发表评论）。因此，您必须在此处提供正确的列表类型。您已经创建了Residences引用的新公寓，那么为什么不将这些Residences合并到自己的列表中呢？

     List<House> houses = new List<House>();
     List<Residence> apartments = new List<Residence>();

     //Create three house objects  and three apartment object with data of your choice. 
     //Then add them to the the above lists.

     Residence ap1 = new Apartment(101,1100);
     Residence ap2 = new Apartment(102,1500);
     Residence ap3 = new Apartment(103,1900);

     Residence hs1 = new House(1,false,1500);
     Residence hs2 = new House(1,true,1900);
     Residence hs3 = new House(2,4,2300);

     apartments.Add(ap1);
     apartments.Add(ap2);
     apartments.Add(ap3);

     houses.Add((House)hs1);
     houses.Add((House)hs2);
     houses.Add((House)hs3);

     //Invoke GetCheapestResidance method by passing either houses list OR department list

     GetCheapestResidance(apartments);

在这里，我已将您的列表更改为列表，就像您当前的代码一样，您没有使用任何公寓列表。房屋也一样。

如果有人对此有更好的解决方案，请随时评论或编辑。

对于第一个错误，请尝试使用+而不是逗号来连接参数，并在item.CalculateCommision()的末尾添加括号以实际获得函数的结果。但是主要的问题是您要在double而不是对象上调用函数。您可以更改Min通话，以进行类似list.OrderBy(x => x.Price).FirstOrDefault()的操作，以最低的价格获得住所并退还。对于第二个错误，请尝试从公寓列表更改为居民列表，以查看是否有帮助。该参数不接受您要传递的类型，但是您应该能够将公寓实例添加到住宅列表中。

子类看不到父方法

如何解决子类看不到父方法

解决方法

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