不包含带有0个参数的构造函数 [英] Does not contain a constructor that takes 0 arguments

问题描述

似乎我得到一个错误，产品不包含一个参数为0的构造函数

  public class Products 
 {
 string id; 
 string name; 
 double price; 
 int soldCount; 
 int stockCount; 
 
 public Products id，string name，double price，
 int soldCount，int stockCount，double tax）
 {
 this.id = id; 
 this.name = name; 
 this.price = price; 
 this.soldCount = soldCount; 
 this.stockCount = stockCount; 
} 
} 
 
 //我有一些获取和设置上面的代码
 //的值，但是它已经太长了，不能放在这里
 
 public class FoodProducts：产品
 {
 public FoodProduct ）
 {
 Console.WriteLine（This is food product）; 
} 
 
 public void Limit（）
 {
 Console .WriteLine（This is a Attribute of a Product）; 
} 
} 
  

解决方案

关于C＃的规则在这里发挥作用：

1. 每个类必须有一个构造函数p>




2. 如果您不提供构造函数，那么将由编译器自动为您提供构造函数。

   
   
   

   这意味着类

     class Demo {} 
     
    
    
    
   编译时提供一个空构造函数，成为
     class Demo {
    public Demo（）{} 
   } 
     
   我可以做
     Demo instance = new Demo（）; 
     
    




3. 如果你提供一个构造函数不产生

     class Demo {
    public Demo（int parameter）{} 
   } 
    
    Demo instance = new Demo（）; //此代码现在失败
    Demo instance = new Demo（3）; //此代码现在成功
     

   这看起来有点反直觉，因为添加代码似乎




4. 当你调用一个派生类的构造函数时，如果不指定要调用的基类构造函数，编译器将调用空基类构造函数，因此

     class Derived：基础{
    public Derived（）{} 
   } 
     

   >
   
   

     class Derived：Base {
    public Derived（）：base（）{} 
   } 
     

因此，为了构造你的派生类，无参数构造函数。看到你如何添加一个构造函数到产品，并且编译器没有生成默认构造函数，你需要显式地添加它在你的代码，如：

  public Products（）
 {
} 
  

显式调用它从派生构造函数

  public FoodProduct（）
：base（string.Empty，string.Empty， 0，0，0，0）
 {
} 
  

Seems that i get an error stating "Products does not contain a constructor that takes 0 arguments

public class Products
{
    string id;
    string name;
    double price;
    int soldCount;
    int stockCount;

    public Products(string id, string name, double price, 
                      int soldCount, int stockCount, double tax)
    {
        this.id = id;
        this.name = name;
        this.price = price;
        this.soldCount = soldCount;
        this.stockCount = stockCount;
    }
}

//I have got some get and set values for the code above 
//but it would have been too long to put in here

public class FoodProducts : Products
{
    public FoodProduct()
    {
        Console.WriteLine("This is food product");
    }

    public void Limit()
    {
        Console.WriteLine("This is an Attribute of a Product");
    }
}

解决方案

Several rules about C# come into play here:

1. Each class must have a constructor (In order to be, well constructed)

2. If you do not provide a constructor, a constructor will be provided for you, free of change, automatically by the compiler.

   This means that the class

   class Demo{}
   

   upon compilation is provided with an empty constructor, becoming

   class Demo{
      public Demo(){}
   }
   

   and I can do

   Demo instance = new Demo();
   

3. If you do provide a constructor (any constructor with any signature), the empty constructor will not be generated

   class Demo{
      public Demo(int parameter){}
   }
   
   Demo instance = new Demo(); //this code now fails
   Demo instance = new Demo(3); //this code now succeeds
   

   This can seem a bit counter-intuitive, because adding code seems to break existing unrelated code, but it's a design decision of the C# team, and we have to live with it.

4. When you call a constructor of a derived class, if you do not specify a base class constructor to be called, the compiler calls the empty base class constructor, so

   class Derived:Base {
      public Derived(){}
   }
   

   becomes

   class Derived:Base {
      public Derived() : base() {}
   }
   

So, in order to construct your derived class, you must have a parameterless constructor on the base class. Seeing how you added a constructor to the Products, and the compiler did not generate the default constructor, you need to explicitly add it in your code, like:

public Products()
{
}

or explicitly call it from the derived constructor

public FoodProduct()
       : base(string.Empty, string.Empty, 0, 0, 0, 0)
{
}

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