Does not contain a constructor that takes 0 arguments

Question

I get an error stating "Products does not contain a constructor that takes 0 arguments" from the following code:

public class Products
{
    string          


        

Answer 1

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)
{
}