Launch activity from non-activity class

I am trying to launch an ActivityB from an ActivityA via a class.

So I create my non-activity class in an ActivityA, this way:

public class ActivityA extends Activity {
    myDialog = new MyDialog(this);

}

And I launch my second activity in the class constructor as follows :

public MyDialog(Context context) {
    Intent i = new Intent (context, ActivityB.class);
    context.startActivity(i);
}

The problem is I would like to acess MyDialog from ActivityB. Is this possible?

Thanks for helping.