Why won't this child class instantiate

Question

I have this code:

class Parent
{
    public Parent(string someArg)
    {
        Console.WriteLine("Parent");
    }

}

class Child : Parent
{
    public Child(string someArg)
    {
        Console.WriteLine("Child");
    }
}

which I then instantiate:

var child = new Child("something");

gets me an error. I know it has to do with the parent constructor, but I'm not sure why is this the case. Am I required to use base every time I have a constructor in the parent which is not parameter-less? Why?

change it to `public Child(string someArg):base(someArg)` to call the constructor of the parent class. — juharr, Mar 04 '16 at 19:01
Possible duplicate of [C# - Making all derived classes call the base class constructor](http://stackoverflow.com/questions/4296888/c-sharp-making-all-derived-classes-call-the-base-class-constructor) — kayess, Mar 04 '16 at 19:08

Allmighty · Accepted Answer · 2016-03-04T19:12:42.650

The base class needs initialization just as well. Therefore, when the base class only has a constructor with an appetite for parameters, you will have to feed it.

In this case, if you are overriding everything the baseclass constructor does, you could let the baseclass have a second, parameterless, constructor. And if you'd like to make use of the logic in the baseclass constructor, you really have no choice but to call : base(string)

Ivan Gritsenko · Answer 2 · 2016-03-04T19:13:44.407

When you declare a class it has a default parameterless constructor. If you define your own construct then default one is gone. In your case you defined a constructor with a parameter.

When you create a new instance each class in inheritance hierarchy should be constructed. Base class has the only constructor with a string parameter which is not called in your code. The implicit parameterless constructor call cannot happen as well.

So that's why you should white:

public Child(string someArg) :base(someArg) { }

Or you can bring the parameterless constructor back in you code and do not use base:

public Parent() { }

score 0 · Answer 3 · answered Mar 04 '16 at 19:04

0

Add this at base class to solve your problem.

public Parent() {}

or make it protected to use it just for child classes

protected Parent() {}

answered Mar 04 '16 at 19:04

M.kazem Akhgary

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Why won't this child class instantiate

3 Answers3