Abstract class > mandatory constructor for child classes

Question

Hi,

How can I write one abstract class that tells that is mandatory for the child class to have one constructor?

Something like this:

public abstract class FatherClass
{

    public **<ChildConstructor>**(string val1, string val2)
    {

    }

   // Someother code....
}

public class ChildClass1: FatherClass
{
    public ChildClass1(string val1, string val2)
    {
       // DO Something.....
    }
}

UPDATE 1:

If I can't inherit constructors. How can I prevent that someone will NOT FORGET to implement that specific child class constructor ????

Answer 1

The problem is that be default a non abstract / static class will always have a default empty public constructor unless you override it with private Constructor(){....}. I don't think you can force a constructor with 2 string params to be present in a child class.

Answer 2

You cannot.

However, you could set a single constructor on the FatherClass like so:

protected FatherClass(string val1, string val2) {}

Which forces subclasses to call this constructor - this would 'encourage' them to provide a string val1, string val2 constructor, but does not mandate it.

I think you should consider looking at the abstract factory pattern instead. This would look like this:

interface IFooFactory {
    FatherClass Create(string val1, string val2);
}

class ChildClassFactory : IFooFactory
{
    public Create(string val1, string val2) {
        return new ChildClass(val1, val2);
}

Wherever you need to create an instance of a subclass of FatherClass, you use an IFooFactory rather than constructing directly. This enables you to mandate that (string val1, string val2) signature for creating them.

Answer 3

You do not inherit constructors. You would simply have to implement one yourself in every child class.

Answer 4

You cant set a constructor as abstract, but you can do something like this:

 public abstract class Test
    {
        public Test(){}

        public Test(int id)
        {
            myFunc(id);
        }

        public abstract void myFunc(int id);
    }