public APropGetter(object obj, AProp <object, PropertyType> aProp)
        {
            _obj   = obj;
            _aProp = aProp;

            _aProp.AddOnPropertyChangedHandler(_obj, OnPropChanged);
        }
 protected override void OnObjSet()
 {
     _aProp.AddOnPropertyChangedHandler(TheObj, OnPropChanged);
 }