Question common property and methods between classes

[johnix]

Hi,
I have some classes that share between their methods and properties: for example class A call method of class B and both class must have common field/property
Common methods/property are several!
I thought of this approach

//------------------------------------------------------
// CLASS 'A'
//------------------------------------------------------
public class A
{


  public A Instance{get{return this;}}
  public IB b;


  public float FieldA;


  public void DoSomethingA()
  {
    FieldA = b.DoSomethingB ();
  }


}


//------------------------------------------------------
// INTERFACE + CLASS 'B'
//------------------------------------------------------
public interface IB
{
  B Instance{get;}
  A a {get;set;}
  float DoSomethingB();
}


public class B:IB
{


  public B Instance{get{return this;}}
  public A a {get;set;}


  public virtual float DoSomethingB()
  {
    return a.FieldA * 0.5F;
  }
}


//------------------------------------------------------
// CLASS B2 
//------------------------------------------------------
public class B2:B
{
  
  public override float DoSomethingB ()
  {
    return a.FieldA  * 2.0F;
  }


}




//------------------------------------------------------
// CLASS TEST 
//------------------------------------------------------


  public class test
{


  public A  a = new A();
  public IB b;


  public test (IB b)
  {


    this.b = b;


    b.a = a.Instance;
    a.b = b.Instance;
    // other




  }
}






    public static void Main (string[] args)
  {


    test t = new test (new B());


    t.a.FieldA = 5;
    t.a.DoSomethingA();


    Console.WriteLine (t.a.FieldA ); // return 2.5




    test t1 = new test (new B2());  // return 10
    t1.a.FieldA = 5;
    t1.a.DoSomethingA();
    
    Console.WriteLine (t1.a.FieldA );
  


  }

Essentially in the class test pass the class instance A to the class B and vice versa (and thus also for future classes).
When i create a new instance of test i decide if use class B or B2 (trough interface).
This approach is correct or i'm in a wrong way?