Constructor initializer does not allow me to use 'this'

Question

Compiler Error Keyword 'this' is not available in the current context

delegate void CallBack(int i);
class A
{
    public A(CallBack cb) { }
}
class B : A
{        
    public B() : base(new CallBack(this.f)){}

    private void f(int i) { }
}

Why is this error ? As a solution I thought of providing a parameterless protected ctor in A() and have

class B : A
{
     public B() : base()   // inherit the new A() ctor
     {
          base.cb = new CallBack(this.f); //this is allowed here
     }
     //...
}

Answer 1

It's because "this" hasn't been created until the base class constructor has run. In your 2nd example the base constructor has finished, and now "this" has meaning.

Answer 2

In the first example the B instance is not initialized yet. In the second, it is.

Answer 3

Since the object is not yet (fully) constructed, that is the base constructor was not yet run, this is not available there.

Answer 4

You should use a abstract/virtual method.

abstract class A {
    A() {
        this.Initialize();
    }

    abstract void Initialize() { }
}

class B : A {
    string Text;

    B() { }

    override void Initialize() {
        this.Text = "Hello world";
    }
}